Changes at the interface of the N- and C-terminal parts of the heavy chain of myosin subfragment 1

Abstract

It has been previously shown that in the M-MgADP-P i state, where the myosin head adopts a pre-power stroke conformation, treatment of trypsin-split subfragment 1 of skeletal muscle myosin with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) results in cross-linking of the C-terminal fragment of the heavy chain of S1 – most probably its converter region – to the N-terminal S1 heavy-chain fragment, generating a product of 44 kDa [Biochim. Biophys. Acta 1481 (2000) 55]. The results described here show that this product is neither generated in the absence of nucleotide nor in the presence of MgADP or MgPP i. The 44 kDa cross-linking product can be formed when S1 treated with EDC is complexed with MgADP-AlF 4 or MgADP-V i (MgADP-P i analogs) and with MgADP-BeF x, MgATPγS or MgAMPPNP (MgATP analogs). The results suggest structural differences between MgATP- or MgADP-P i-bound S1, and MgADP-bound or nucleotide-free S1, in spatially close regions of their N- and C-terminal heavy-chain fragments.