title: The conformation of cross-linked actin.S-1 in the presence and absence of ATP.
abstract: Electron microscopy studies have shown that the structure of the complex of myosin subfragment 1 (S-1) cross-linked to actin with 1-ethyl-3-[3-(dimethyl-amino) propyl] carbodiimide is very different in the presence and absence of ATP (Craig, R., Greene, L. E., and Eisenberg, E. (1985) Proc. Natl. Acad. Sci. U. S. A. 82, 3247-3251). More recent studies have found that the structure of the cross-linked complex between S-1 modified extensively with N-ethylmaleimide (NEM.S-1) and actin resembles that of the rigor complex both in the presence and absence of ATP, whereas the structure of the cross-linked complex between S-1 modified with N',N'-p-phenylenedimaleimide (pPDM.S-1) and actin resembles that of the cross-linked actin.S-1 complex in the presence of ATP. In the present study, we have obtained biochemical evidence supporting these results. The conformation of the different cross-linked actin.S-1 complexes was determined by studying their effect on the troponin-tropomyosin-actin complex (regulated actin). The basis of this probe for conformation is that S-1.ATP, which is in the weak-binding conformation, interacts very differently with regulated actin than S-1 or S-1.ADP, which are in the strong-binding conformation. We find that both in the presence and absence of ATP, cross-linked NEM.S-1 appears to be in the strong-binding conformation, whereas cross-linked pPDM.S-1 appears to be shifted toward the weak-binding conformation. In contrast, cross-linked unmodified S-1 appears to be in the strong-binding conformation in the presence of ADP and the weak-binding conformation in the presence of ATP. Therefore, in agreement with electron microscopy studies, the cross-linked actin.S-1 complex appears to be able to alternate between the weak-binding and strong-binding conformation during the cross-bridge cycle.
mesh_terms: D000199:Actins / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D005022:Ethyldimethylaminopropyl Carbodiimide / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D008301:Maleimides / Q000494:pharmacology; D008854:Microscopy, Electron; D010446:Peptide Fragments / Q000378:metabolism*; D011487:Protein Conformation / Q000187:drug effects; D011817:Rabbits
chemical_list: D000199:Actins; D008301:Maleimides; D010446:Peptide Fragments; C033025:actin subfragments; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D005033:Ethylmaleimide; D005022:Ethyldimethylaminopropyl Carbodiimide; C023860:N,N'-2-phenylenedimaleimide