ALLOSTERY, COOPERATIVITY, AND DIFFERENT STRUCTURAL STATES IN F-ACTIN

Electron microscopy and three-dimensional reconstructions have been us ed to show that F-actin can exist in multiple states. We have also bee n able to visualize large allosteric effects involving the C-terminus, the nucleotide binding site, the high-affinity metal-binding site, an d the DNase I-binding loop. Further, there exists a large degree of co operativity in F-actin, such that conformational changes at one end of a filament may be transmitted to the other, distant, end. While many of these allosteric and cooperative effects have been previously sugge sted to exist based upon biochemical observations, we have been able t o observe that these effects probably involve the movement of a large number of residues over significant distances. In systems such as musc le some of these conformational changes in F-actin may play an importa nt role. (C) 1995 Academic Press, Inc. Press, Inc.