Direct Cross-Linking of Three Domains in the Myosin Head

Abstract

To obtain information about domain-domain contacts in the myosin head, trypsinsplit myosin subfragment-1 (S-1), which mainly consists of 50 K, 26 K, and 20 K fragments, was cross-linked directly by the photodynamic technique under mild conditions (pH 7-8.5, 0°C) using riboflavin 5'-phosphate, protoporphyrin, and methylene blue as sensitizers. Exposure of trypsin split-chymotryptic S-1 to visible light in the presence of the sensitizers resulted in formation of cross-linked products of (20+26) K, (20+50) K, (26+50) K, and (20+26+50) K fragments. The results suggest that three domains in the myosin head are in contact with each other, at least partly, raising the possibility that the communication between the ATP- and actin-binding sites passes through a “short cut, ” i.e., the contact region between the domains.