Modulation of the Interaction Between G-Actin and Thymosin β4by the ATP/ADP Ratio: Possible Implication in the Regulation of Actin Dynamics

The interaction of G-actin with thymosin β4(Tβ4), the major G-actin-sequestering protein in motile and proliferating cells, has been analyzed in vitro. Tβ4is found to have a 50-fold higher affinity for MgATP-actin than for MgADP-actin. These results imply that in resting platelets and neutrophils, a...

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Published in:Proceedings of the National Academy of Sciences - PNAS 1993-06, Vol.90 (11), p.5034-5038
Main Authors: Carlier, Marie-France, Jean, Catherine, Rieger, Klaus J., Lenfant, Maryse, Pantaloni, Dominique
Format: Article
Language:English
Subjects:
Actins
Analytical, structural and metabolic biochemistry
Biochemistry
Biological and medical sciences
Contractile proteins
Fundamental and applied biological sciences. Psychology
Holoproteins
Kinetics
Neutrophils
Nucleotides
Physiological regulation
Platelets
Polymerization
Profilins
Proteins
Spleen
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Summary:The interaction of G-actin with thymosin β4(Tβ4), the major G-actin-sequestering protein in motile and proliferating cells, has been analyzed in vitro. Tβ4is found to have a 50-fold higher affinity for MgATP-actin than for MgADP-actin. These results imply that in resting platelets and neutrophils, actin is sequestered by Tβ4as MgATP-G-actin. Kinetic experiments and theoretical calculations demonstrate that this ATP/ADP dependence of Tβ4affinity for G-actin can generate a mechanism of desequestration of G-actin by ADP, in the presence of physiological concentrations of Tβ4(≈0.1 mM). The desequestration of G-actin by ADP is kinetically enhanced by profilin, which accelerates the dissociation of ATP from G-actin. Whether a local drop in the ATP/ADP ratio can allow local, transient desequestration and polymerization of actin either close to the plasma membrane, following platelet or neutrophil stimulation, or behind the Listeria bacterium in the host cell, while the surrounding cytoplasm contains sequestered ATP-G-actin, is an open issue raised by the present work.
ISSN:0027-8424
1091-6490