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

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), MgATP gamma S 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.