1: Biochim Biophys Acta. 2006 May-Jun;1763(5-6):450-62. Epub 2006 Mar 29.


Interactions of mitochondria with the actin cytoskeleton.

Boldogh IR, Pon LA.

Department of Anatomy and Cell Biology, Columbia University College of Physicians and Surgeons, 12-425, 630 West 168th Street, New York, NY 10032, USA.

Interactions between mitochondria and the cytoskeleton are essential for normal mitochondrial morphology, motility and distribution. While microtubules and their motors have been established as important factors for mitochondrial transport, emerging evidence indicates that mitochondria interact with the actin cytoskeleton in many cell types. In certain fungi, such as the budding yeast and Aspergillus, or in plant cells mitochondrial motility is largely actin-based. Even in systems such as neurons, where microtubules are the primary means of long-distance mitochondrial transport, the actin cytoskeleton is required for short-distance mitochondrial movements and for immobilization of the organelle at the cell cortex. The actin cytoskeleton is also involved in the immobilization of mitochondria at the cortex in cultured tobacco cells and in budding yeast. While the exact nature of these immobilizations is not known, they may be important for retaining mitochondria at sites of high ATP utilization or at other cellular locations where they are needed. Recent findings also indicate that mutations in actin or actin-binding proteins can influence mitochondrial pathways leading to cell death. Thus, mitochondria-actin interactions contribute to apoptosis.

Publication Types:
Research Support, N.I.H., Extramural
Review

PMID: 16624426 [PubMed - indexed for MEDLINE]

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2: Dev Cell. 2005 Jul;9(1):3-17.


Bacteria-host-cell interactions at the plasma membrane: stories on actin cytoskeleton subversion.

Rottner K, Stradal TE, Wehland J.

Cytoskeleton Dynamics Group, German Research Center for Biotechnology, Mascheroder Weg 1, D-38124 Braunschweig, Germany.

Exploitation of the host-cell actin cytoskeleton is pivotal for many microbial pathogens to enter cells, to disseminate within and between infected tissues, to prevent their uptake by phagocytic cells, or to promote intimate attachment to the cell surface. To accomplish this, these pathogens have evolved common as well as unique strategies to modulate actin dynamics at the plasma membrane, which will be discussed here, exemplified by a number of well-studied bacterial pathogens.

Publication Types:
Research Support, Non-U.S. Gov't
Review

PMID: 15992537 [PubMed - indexed for MEDLINE]

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3: Cell Mol Life Sci. 2005 May;62(10):1081-99.


Integrin-actin interactions.

Wiesner S, Legate KR, Fässler R.

Department of Molecular Medicine, Max-Planck-Institut of Biochemistry, Martinsried, Germany. wiesner@biochem.mpg.de

The integrin family of extracellular matrix receptors regulates many aspects of cell life, in particular cell adhesion and migration. These two processes depend on organization of the actin cytoskeleton into adhesive and protrusive organelles in response to extracellular signals. Integrins are important switch points for the spatiotemporal control of actin-based motility in higher eukaryotes. Ligands of integrin cytoplasmic tails are central elements of signalling pathways involving small GTPases as well as protein and lipid kinases in the regulation of Factin crosslinking, actin treadmilling and de novo nucleation of actin filaments. We present an overview of common pathways and discuss recent evidence for their differential use by individual integrin receptors.

Publication Types:
Research Support, Non-U.S. Gov't
Review

PMID: 15761669 [PubMed - indexed for MEDLINE]

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4: Traffic. 2004 Aug;5(8):571-6.


Annexin-actin interactions.

Hayes MJ, Rescher U, Gerke V, Moss SE.

Division of Cell Biology, Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V 9EL, UK.

The actin cytoskeleton is a malleable framework of polymerised actin monomers that may be rapidly restructured to enable diverse cellular activities such as motility, endocytosis and cytokinesis. The regulation of actin dynamics involves the coordinated activity of numerous proteins, among which members of the annexin family of Ca2+- and phospholipid-binding proteins play an important role. Although the roles of annexins in actin dynamics are not understood at a mechanistic level, annexins have the requisite properties to integrate Ca2+-signaling with actin dynamics at membrane contact sites. In this review we discuss the current state of knowledge on this topic, and consider how and where annexins may fit into the complex molecular machinery that regulates the actin cytoskeleton. Copyright 2004 Blackwell Munksgaard

Publication Types:
Research Support, Non-U.S. Gov't
Review

PMID: 15260827 [PubMed - indexed for MEDLINE]

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5: Cell Mol Life Sci. 2003 Nov;60(11):2347-55.


Specific interactions of the adenovirus proteinase with the viral DNA, an 11-amino-acid viral peptide, and the cellular protein actin.

Mangel WF, Baniecki ML, McGrath WJ.

Biology Department, Brookhaven National Laboratory, 50 Bell Avenue, Upton, New York 11973, USA. mangel@bnl.gov

The adenovirus proteinase (AVP) is synthesized in an inactive form that requires cofactors for activation. The interaction of AVP with two viral cofactors and with a cellular cofactor, actin, is characterized by quantitative analyses. The results are consistent with a specific model for the regulation of AVP. Late in adenovirus infection, inside nascent virions, AVP becomes partially activated by binding to the viral DNA, allowing it to cleave out an 11-amino-acid viral peptide, pVIc, that binds to AVP and fully activates it. Then, about 70 AVP-pVIc complexes move along the viral DNA, via one-dimensional diffusion, cleaving virion precursor proteins 3200 times to render a virus particle infectious. Late in adenovirus infection, in the cytoplasm, the cytoskeleton is destroyed. The amino acid sequence of the C terminus of actin is homologous to that of pVIc, and actin, like pVIc, can act as a cofactor for AVP in the cleavage of cytokeratin 18 and of actin itself. Thus, AVP may also play a role in cell lysis.

Publication Types:
Research Support, U.S. Gov't, Non-P.H.S.
Research Support, U.S. Gov't, P.H.S.
Review

PMID: 14625681 [PubMed - indexed for MEDLINE]

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6: J Muscle Res Cell Motil. 2002;23(7-8):697-702.


Dictyostelium myosin II as a model to study the actin-myosin interactions during force generation.

Sasaki N, Ohkura R, Sutoh K.

Center for Interdisciplinary Research, Tohoku University, Aramaki-aza-aoba, Aoba-ku, Sendai, Miyagi 980-8579, Japan.

During steady-state ATP hydrolysis by actomyosin, myosin cyclically passes through strong actin-binding states and weak actin-binding states, depending on the nature of a nucleotide in the ATPase site. This cyclic change of actin-myosin affinity is coupled with the lever-arm swing and is critical for the sliding motion and force generation of actomyosin. To understand the structure-function relationship of this ATPase-dependent actin-myosin interaction, Dictyostelium myosin II has been extensively used for site-directed mutagenesis. By generating a large number of mutant myosins, two hydrophobic actin-binding sites have been revealed, located at the tip of the upper and lower 50 K subdomains of Dictyostelium myosin, one of which is the 'cardiomyopathy loop'. Furthermore, the slight change in relative orientation of these two hydrophobic sites around the 'strut loop' has been shown to work as a switch to turn on and off the strong binding to actin. Once the switch is turned off, myosin enters in the weak-binding state, where ionic interactions between actin and the 'loop 2' of myosin become the dominant force to maintain the actin-myosin association. The details of actin-myosin interactions revealed by the Dictyostelium system can serve as a framework for further examinations of the myosin superfamily proteins.

Publication Types:
Review

PMID: 12952068 [PubMed - indexed for MEDLINE]

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7: Nat Cell Biol. 2003 Jul;5(7):599-609.


Conserved microtubule-actin interactions in cell movement and morphogenesis.

Rodriguez OC, Schaefer AW, Mandato CA, Forscher P, Bement WM, Waterman-Storer CM.

Department of Cell Biology, The Scripps Research Institute, 10550 N. Torrey Pines Rd., La Jolla, CA 92037, USA.

Interactions between microtubules and actin are a basic phenomenon that underlies many fundamental processes in which dynamic cellular asymmetries need to be established and maintained. These are processes as diverse as cell motility, neuronal pathfinding, cellular wound healing, cell division and cortical flow. Microtubules and actin exhibit two mechanistic classes of interactions--regulatory and structural. These interactions comprise at least three conserved 'mechanochemical activity modules' that perform similar roles in these diverse cell functions.

Publication Types:
Research Support, U.S. Gov't, Non-P.H.S.
Research Support, U.S. Gov't, P.H.S.
Review

PMID: 12833063 [PubMed - indexed for MEDLINE]

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8: J Exp Biol. 2003 Jun;206(Pt 12):1971-6.


Force-velocity relationships in actin-myosin interactions causing cytoplasmic streaming in algal cells.

Sugi H, Chaen S.

Department of Physiology, School of Medicine, Teikyo University, Itabashi-ku, Tokyo 173-8605, Japan. sugi@med.teikyo-u.ac.jp

Cytoplasmic streaming in giant internodal cells of green algae is caused by ATP-dependent sliding between actin cables fixed on chloroplast rows and cytoplasmic myosin molecules attached to cytoplasmic organelles. Its velocity (>/=50 micro m s(-1)) is many times larger than the maximum velocity of actin-myosin sliding in muscle. We studied kinetic properties of actin-myosin sliding causing cytoplasmic streaming in internodal cell preparations of Chara corallina, into which polystyrene beads, coated with cytoplasmic myosin molecules, were introduced. Constant centrifugal forces directed opposite to the bead movement were applied as external loads. The steady-state force-velocity (P-V) curves obtained were nearly straight, irrespective of the maximum isometric force generated by cytoplasmic myosin molecules, indicating a large duty ratio of cytoplasmic myosin head. The large velocity of cytoplasmic streaming can be accounted for, at least qualitatively, by assuming a mechanically coupled interaction between cytoplasmic myosin heads as well as a large distance of unitary actin-myosin sliding.

Publication Types:
Review

PMID: 12756278 [PubMed - indexed for MEDLINE]

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9: Cardiovasc Pathol. 2002 May-Jun;11(3):135-40.


Microtubule-actin interactions may regulate endothelial integrity and repair.

Lee JS, Gotlieb AI.

Department of Pathology, University Health Network, University of Toronto, Ontario, Canada.

An important mechanism for the initiation and progression of atherosclerosis is the loss of endothelial integrity, which is required for normal blood vessel function. The important components of the endothelial cell cytoskeleton system that regulate endothelial integrity include actin microfilaments and microtubules, which are both associated with protein complexes that regulate cell-cell and cell-substratum adhesion. To date, studies have shown that microfilaments are essential in maintaining the structural integrity of the endothelium while microtubules regulate the directional cell migration during repair. When microtubules are disrupted at the onset of wounding, neither centrosome reorientation, which is essential for efficient endothelial cell wound repair, nor cell migration occurs. Disruption of microfilaments is also associated with inefficient endothelial cell migration and repair. How then might these systems be associated with one another? Linker proteins, which may facilitate interaction between microtubules and actin microfilaments, have recently been identified in nonendothelial systems. It is likely that microtubule-microfilament interactions are important in the complex regulation of endothelial integrity and repair especially as they relate to atherosclerotic plaque formation.

Publication Types:
Review

PMID: 12031763 [PubMed - indexed for MEDLINE]

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10: Results Probl Cell Differ. 2002;36:7-19.


Changes in actin and myosin structural dynamics due to their weak and strong interactions.

Thomas DD, Prochniewicz E, Roopnarine O.

Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA.

Figure 3 summarizes the effects of actomyosin binding on the internal and global dynamics of either protein, as discussed in this chapter. These effects depend primarily on the strength of the interaction; which in turn depends on the state of the nucleotide at the myosin active site. When either no nucleotide or ADP is bound, the interaction is strong and the effect on each protein is maximal. When the nucleotide is ATP or ADP.Pi, or the equivalent nonhydrolyzable analogs, the interaction is weak and the effect on molecular dynamics of each protein is minimal. The weaker effects in weak-binding states are not simply the reflection of lower occupancy of binding sites--the molecular models in Fig. 3 illustrate the effects of the formation of the ternary complex, after correction for the free actin and myosin in the system. Thus EPR on myosin (Berger and Thomas 1991; Thomas et al. 1995) and pyrene fluorescence studies on actin (Geeves 1991) have shown that the formation of a ternary complex has a negligible effect on the internal dynamics of both [figure: see text] proteins (left side of Fig. 3, white arrows). As shown by both EPR (Baker et al. 1998; Roopnarine et al. 1998) and phosphorescence (Ramachandran and Thomas 1999), both domains of myosin are dynamically disordered in weak-binding states, and this is essentially unaffected by the formation of the ternary complex (left side of Fig. 3, indicated by disordered myosin domains). The only substantial effect of the formation of the weak interaction that has been reported is the EPR-detected (Ostap and Thomas 1991) restriction of the global dynamics of actin upon weak myosin binding (left column of Fig. 3, gray arrow). The effects of strong actomyosin formation are much more dramatic. While substantial rotational dynamics, both internal and global, exist in both myosin and actin in the presence of ADP or the absence of nucleotides, spin label EPR, pyrene fluorescence, and phosphorescence all show dramatic restrictions in these motions upon formation of the strong ternary complex (right column of Fig. 3). One implication of this is that the weak-to-strong transition is accompanied by a disorder-to-order transition in both actin and myosin, and this is itself an excellent candidate for the structural change that produces force (Thomas et al. 1995). Another clear implication is that the crystal structures obtained for isolated myosin and actin are not likely to be reliable representations of structures that exist in ternary complexes of these proteins (Rayment et al. 1993a and 1993b; Dominguez et al. 1998; Houdusse et al. 1999). This is clearly true of the strong-binding states, since the spectroscopic studies indicate consistently that substantial changes occur in both proteins upon strong complex formation. For the weak complexes, the problem is not that complex formation induces large structural changes, but that the structures themselves are dynamically disordered. This is probably why so many different structures have been obtained for myosin S1 with nucleotides bound--each crystal is selecting one of the many different substates represented by the dynamic ensemble. Finally, there is the problem that the structures of actomyosin complexes are probably influenced strongly by their mechanical coupling to muscle protein lattice (Baker at al. 2000). Thus, even if co-crystals of actin and myosin are obtained in the future, an accurate description of the structural changes involved in force generation will require further experiments using site-directed spectroscopic probes of both actin and myosin, in order to detect the structural dynamics of these ternary complexes under physiological conditions.

Publication Types:
Review

PMID: 11892285 [PubMed - indexed for MEDLINE]

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11: Results Probl Cell Differ. 2002;36:31-49.


Insights into actomyosin interactions from actin mutations.

Doyle TC, Reisler E.

Xenogen Corporation, 860 Atlantic Avenue, Alameda, California 94501, USA.

Publication Types:
Research Support, U.S. Gov't, Non-P.H.S.
Research Support, U.S. Gov't, P.H.S.
Review

PMID: 11892282 [PubMed - indexed for MEDLINE]

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12: Methods Mol Biol. 2001;161:229-39.


Xenopus egg extracts as a model system for analysis of microtubule, actin filament, and intermediate filament interactions.

Mandato CA, Weber KL, Zandy AJ, Keating TJ, Bement WM.

Department of Zoology, University of Wisconsin, Madison, WI, USA.

Publication Types:
Review

PMID: 11190509 [PubMed - indexed for MEDLINE]

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13: Cell Signal. 2000 Feb;12(2):71-9.


Thrombin-induced phosphorylation of MARCKS does not alter its interactions with calmodulin or actin.

Neltner BS, Zhao Y, Sacks DB, Davis HW.

Department of Internal Medicine (Pulmonary and Critical Care Medicine), University of Cincinnati Medical Center, Cincinnati, OH 45267-0564, USA.

Myristoylated alanine-rich C kinase substrate (MARCKS) is a calmodulin (CaM)- and actin-binding protein and prominent protein kinase C (PKC) substrate. In vitro phosphorylation of MARCKS by PKC has been shown to induce the release of both CaM and actin, leading to the suggestion that MARCKS may regulate CaM availability during agonist-induced signalling. In support of this hypothesis we previously demonstrated that thrombin-induced MARCKS phosphorylation in endothelial cells (EC) parallels activation of myosin light chain kinase, a CaM-dependent enzyme. To test this theory further, we transfected CHO cells, which normally do not express significant levels of MARCKS, with a MARCKS cDNA. The thrombin-stimulated phosphorylation of myosin light chains and the sensitivity to CaM antagonists in the MARCKS overexpressing cells was the same as that in control CHO cells. MARCKS associated with the actin cytoskeleton in EC was markedly increased upon treatment with the PKC activator, PMA, but only modestly enhanced by thrombin treatment. Similarly, colocalisation of MARCKS with actin was enhanced when the EC were challenged with PMA but not thrombin. These data may be partially explained by PKC-independent phosphorylation of MARCKS in response to thrombin stimulation.

Publication Types:
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, P.H.S.
Review

PMID: 10679575 [PubMed - indexed for MEDLINE]

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14: Curr Opin Cell Biol. 1999 Feb;11(1):61-7.


Positive feedback interactions between microtubule and actin dynamics during cell motility.

Waterman-Storer CM, Salmon E.

Department of Biology 607 Fordham Hall University of North Carolina Chapel Hill NC 27599-3280 USA. waterman@email.unc.edu

The migration of tissue cells requires interplay between the microtubule and actin cytoskeletal systems. Recent reports suggest that interactions of microtubules with actin dynamics creates a polarization of microtubule assembly behavior in cells, such that microtubule growth occurs at the leading edge and microtubule shortening occurs at the cell body and rear. Microtubule growth and shortening may activate Rac1 and RhoA signaling, respectively, to control actin dynamics. Thus, an actin-dependent gradient in microtubule dynamic-instability parameters in cells may feed back through the activation of specific signalling pathways to perpetuate the polarized actin-assembly dynamics required for cell motility.

Publication Types:
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, P.H.S.
Review

PMID: 10047528 [PubMed - indexed for MEDLINE]

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15: Acta Physiol Scand. 1998 Dec;164(4):401-14.


Structural interactions between actin, tropomyosin, caldesmon and calcium binding protein and the regulation of smooth muscle thin filaments.

Marston S, Burton D, Copeland O, Fraser I, Gao Y, Hodgkinson J, Huber P, Levine B, el-Mezgueldi M, Notarianni G.

Imperial College School of Medicine, National Heart and Lung Institute, London, UK.

The basic structure and functional properties of smooth muscle thin filaments were established about 10 years ago. Since then we and others have been working on the details of how tropomyosin, caldesmon and the Ca(2+)-binding protein regulate actin interaction with myosin. Our work has tended to emphasize the similarities between caldesmon and troponin function whilst others have been more concerned with the differences. The need to resolve the resulting differences has stimulated us to find new and more direct ways of investigating the mechanism of thin filament regulation. In recent years an apparent divergence has opened up between functional measurements, which indicate an allosteric-cooperative regulatory mechanism in which caldesmon and Ca(2+)-binding protein control actin-tropomyosin state in the same way as troponin, and structural measurements which show thin filament structures unlike striated muscle thin filaments. The challenge is to interpret function in terms of structure. We have combined functional studies with expression and mutagenesis of caldesmon and with structural methods including X-ray crystalography of tropomyosin-caldesmon crystals, electron microscopy and helical reconstruction of actin-tropomyosin-caldesmon complexes and high resolution nuclear magnetic resonance spectroscopy of the C-terminus of caldesmon in interaction with actin and calmodulin. We have used this information to propose a structural mechanism for caldesmon regulation of the smooth muscle thin filament.

Publication Types:
Research Support, Non-U.S. Gov't
Review

PMID: 9887964 [PubMed - indexed for MEDLINE]

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16: EMBO J. 1998 Jul 15;17(14):3797-806.


Interactions of Listeria monocytogenes with mammalian cells during entry and actin-based movement: bacterial factors, cellular ligands and signaling.

Cossart P, Lecuit M.

Unité des Interactions Bactéries Cellules, Institut Pasteur, 28 Rue du Docteur Roux, Paris 75015, France. pcossart@pasteur.fr

Although <50 kb of its 3.3 megabase genome is known, Listeria monocytogenes has received much attention and an impressive amount of data has contributed in raising this bacterium among the best understood intracellular pathogens. The mechanisms that Listeria uses to enter cells, escape from the phagocytic vacuole and spread from one cell to another using an actin-based motility process have been analysed in detail. Several bacterial proteins contributing to these events have been identified, including the invasion proteins internalin A (InlA) and B (InlB), the secreted pore-forming toxin listeriolysin O (LLO) which promotes the escape from the phagocytic vacuole, and the surface protein ActA which is required for actin polymerization and bacterial movement. While LLO and ActA are critical for the infectious process and are not redundant with other listerial proteins, the precise role of InlA and InlB in vivo remains unclear. How InlA, InlB, LLO or ActA interact with the mammalian cells is beginning to be deciphered. The picture that emerges is that this bacterium uses general strategies also used by other invasive bacteria but has evolved a panel of specific tools and tricks to exploit mammalian cell functions. Their study may lead to a better understanding of important questions in cell biology such as ligand receptor signalling and dynamics of actin polymerization in mammalian cells.

Publication Types:
Research Support, Non-U.S. Gov't
Review

PMID: 9669997 [PubMed - indexed for MEDLINE]

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17: Circ Res. 1998 Jun 1;82(10):1109-10.


Comment on:
Circ Res. 1998 Jun 1;82(10):1029-34.

How actin-myosin interactions differ with different isoforms of myosin.

Winegrad S.

Publication Types:
Comment
Editorial
Review

PMID: 9622164 [PubMed - indexed for MEDLINE]

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18: Tanpakushitsu Kakusan Koso. 1997 May;42(7 Suppl):1209-14.


[Imaging of intermolecular interactions: focused on actin-myosin interactions]

[Article in Japanese]

Tokunaga M.

Biomotron Project, ERATO, JST, Osaka, Japan.

Publication Types:
Review

PMID: 9170955 [PubMed - indexed for MEDLINE]

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19: Annu Rev Genet. 1997;31:113-38.


Host-pathogen interactions during entry and actin-based movement of Listeria monocytogenes.

Ireton K, Cossart P.

Unité des Interactions Bactéries-Cellules, Institut Pasteur, Paris, France.

Listeria monocytogenes is a pathogenic bacterium that induces its own uptake into mammalian cells, and spreads from one cell to another by an actin-based motility process. Entry into host cells involves the bacterial surface proteins InlA (internalin) and InlB. The receptor for InlA is the cell adhesion molecule E-cadherin. InlB-mediated entry requires activation of the host protein phosphoinositide (PI) 3-kinase, probably in response to engagement of a receptor. Actin-based movement of L. monocytogenes is mediated by the bacterial surface protein ActA. The N-terminal region of this protein is necessary and sufficient for polymerization of host cell actin. Other host proteins involved in bacterial motility include profilin, Vasodilator-Stimulated Phosphoprotein (VASP), the Arp2/Arp3 complex, and cofilin. Studies of entry and intracellular movement of L. monocytogenes could lead to a better understanding of receptor-ligand signaling and dynamics of actin polymerization in mammalian cells.

Publication Types:
Research Support, Non-U.S. Gov't
Review

PMID: 9442892 [PubMed - indexed for MEDLINE]

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20: Curr Opin Cell Biol. 1994 Feb;6(1):120-30.


Membrane interactions with the actin cytoskeleton.

Hitt AL, Luna EJ.

Worcester Foundation for Experimental Biology, Shrewsbury, MA 01545.

Recent advances have been made in our understanding of the direct binding of actin to integral membrane proteins. New information has been obtained about indirect actin-membrane associations through spectrin superfamily members and through proteins at the cytoplasmic surfaces of focal contacts and adherens junctions.

Publication Types:
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, P.H.S.
Review

PMID: 8167017 [PubMed - indexed for MEDLINE]

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21: Adv Exp Med Biol. 1994;358:35-49.


Actin-bound nucleotide/divalent cation interactions.

Gershman LC, Selden LA, Kinosian HJ, Estes JE.

Research Service, Stratton VA Medical Center, Albany, New York 12208.

At this point, it may be worthwhile to list, in summary form, the important aspects of divalent cation and nucleotide binding to actin that have been reviewed here: 1) High affinity divalent cation binding to actin is very tight, with equilibrium dissociation constant KCa approximately 1 nM and KMg approximately 5 nM at pH 7.0. 2) The binding kinetics of Ca++ are diffusion limited. Dissociation is slow, with k-Ca approximately 0.015 sec at pH 7.0 (and low ionic strength). 3) The binding kinetics of Mg++ are limited by the characteristics of the Mg++ aquo-ion and are much slower than for Ca++; k-Mg approximately 0.0012 at pH 7.0. 4) Increase in pH or ionic strength weakens divalent cation binding at the high affinity site, primarily by increasing k-Ca and k-Mg. 5) Exchange of Mg++ for Ca++ (or vice versa) at the high affinity site is by a competitive pseudo-first order process with an apparent rate constant (kapp) intermediate between k-Ca and k-Mg and dependent upon the cation concentration ratio [Ca]/[Mg] present. 6) High affinity ATP binding is modulated by the high affinity divalent cation. The cation concentration range over which this modulation occurs is about 100-fold higher for Mg++ than for Ca++, again because of the different characteristics of the Mg++ and Ca++ aquo-ions. 7) At low divalent cation concentrations, ATP dissociation from actin is limited by dissociation of the tightly-bound divalent cation. 8) At high divalent cation concentrations, ATP dissociation probably occurs via dissociation of the divalent cation-nucleotide complex and is quite slow, with dissociation rate constant approximately 0.0005 sec-1. 9) Competitive nucleotide exchange on actin may be described by a pseudo-first order model analogous to that for divalent cation exchange. The pseudo-first order rate constants depend upon the divalent cation concentration. The overall nucleotide exchange rate constant kex depends upon these constants and the solution nucleotide concentration ratio, e.g. [ATP]/[ADP]. The following circumstances develop from the characteristics of the high affinity binding of divalent cation and nucleotide to actin: 1) The standard methods for actin preparation convert in vivo Mg-actin into Ca-actin. 2) Converting Ca-actin back to Mg-actin is not easy. A very low ratio of [Ca]/[Mg] is necessary, which usually requires the use of Ca-cheltors, and a long time (5-10 min) must be allowed for complete exchange.(ABSTRACT TRUNCATED AT 400 WORDS)

Publication Types:
Research Support, U.S. Gov't, Non-P.H.S.
Research Support, U.S. Gov't, P.H.S.
Review

PMID: 7801810 [PubMed - indexed for MEDLINE]

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22: J Muscle Res Cell Motil. 1991 Apr;12(2):136-44.


Actin binding proteins--lipid interactions.

Isenberg G.

Biophysics Dept. Technical University of Munich, Garching, Germany.

Publication Types:
Review

PMID: 1648107 [PubMed - indexed for MEDLINE]

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23: J Cell Sci Suppl. 1991;14:31-5.


The influence of pressure on actin and myosin interactions in solution and in single muscle fibres.

Geeves MA.

Department of Biochemistry, School of Medical Sciences, University of Bristol, UK.

Studies of the molecular mechanism of motile activity require the capacity to examine the properties of individual, isolated molecular components and the properties of these same molecular components in the organised system. Pressure perturbation is one method which can be applied to motile systems at different levels of organisation. We show here that pressure perturbs a specific interaction between actin and myosin in solution and also perturbs the cycling crossbridge in a contracting muscle.

Publication Types:
Research Support, Non-U.S. Gov't
Review

PMID: 1885656 [PubMed - indexed for MEDLINE]

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24: Tanpakushitsu Kakusan Koso. 1985 Nov;30(12):1290-300.


[Interactions between actin and actin-binding proteins]

[Article in Japanese]

Sutoh K.

Publication Types:
Review

PMID: 3911286 [PubMed - indexed for MEDLINE]