Nucleotide-induced change in the interaction between the 20- and 26-kilodalton heavy-chain segments of myosin adenosine triphosphatase revealed by chemical cross-linking via the reactive thiol SH2

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Abstract
When myosin subfragment 1 (S-1) reacts with the bifunctional reagents with cross-linking spans of 3-4.5 .ANG., p-nitrophenyl iodoacetate and p-nitrophenyl bromoacetate, the 20-kilodalton (20-kDa) segment of the heavy chain is cross-linked to the 26-kDa segment via the reactive thiol SH2. The well-defined reactive lysyl residue Lys-83 of the 26-kDa segment was not involved in the cross-linking. The cross-linking was completely abolished by nucleotides. Taking into acount the recent report that SH2 is cross-linked to a thiol of the 50-kDa segment of S-1 using a reagent with a cross-linking span of 2 .ANG. [Chaussepied, P., Mornet, D., and Kassab, R. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 2037-2041], present results suggest that SH2 of S-1 lies close to both the 26- and 50-kDa segments of the heavy chain. The data also encourage us to confirm our previous suggestion that the ATPase site of S-1 resides at or near the region where all three segments of 26, 50, and 20 kDa are contiguous [Hiratsuka, T. (1984) J. Biochem. (Tokyo) 96, 269-272; Hiratsuka, T. (1985) J. Biochem. (Tokyo) 97, 71-78].

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