RESTORATION OF DEFECTIVE MECHANOCHEMICAL PROPERTIES OF CLEAVED ACTINSBY NATIVE TROPOMYOSIN - INVOLVEMENT OF THE 40-50 LOOP IN SUBDOMAIN 2 OF ACTIN IN INTERACTION WITH MYOSIN AND TROPOMYOSIN

Native tropomyosin activated sliding movement in vitro of F-actin with ATP by 30 %, Actin cleaved at the 40-50 loop by subtilisin or protein ase K slid on HMM much slower than intact actin, but native tropomyosi n strikingly recovered this defective motility of cleaved actin by 2 t o 3 times, On the other hand, with ATP analogues of CTP and ITP, slidi ng movements of cleaved actin and particularly intact actin were inhib ited by native tropomyosin, indicating that native tropomyosin augment ed specificity of the myosin substrate of NTP. These results suggested that the 40-50 loop in the small domain 2 of actin interacted directl y or indirectly with tropomyosin and play a significant role in cross talk between myosin and native tropomyosin. (C) 1997 Academic Press.