Flexibility of the myosin heavy chain: direct evidence that the region containing SH1 and SH2 can move 10 A under the influence of nucleotide binding.

摘要: Previous experiments demonstrated that two thiols of skeletal myosin subfragment 1 (SF/sub 1/) could be oxidized to a disulfide bond by treatment with 2-fold excess 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) in the presence MgADP. The resulting characteristic changes ATPase activities SF/sub 1/ and fact MgADP was stably trapped at active site, suggested cross-linked were SH/sub (Cys-707) 2/ (Cys-697) from heavy chain. To verify this suggestion, 1/, after DTNB as above, treated an N-ethylmaleimide block all accessible thiols. single protein produced oxidation reduced dithioerythritol modified internally equimolar (/sup 14/C)p-phenylenedimaleimide (pPDM) After extensive trypsinization, major /sup 14/C-labeled peptide isolated, characterized, shown Cys-Asn-Gly-Val-Leu-Gly-Ile-Arg-Ile-Cys-Arg, which cysteines pPDM. This is known contain order come residues 697-708 rabbit Parallel 14/C)pPDM unmodified similar those above gave identical more » tryptic peptide, verifying earlier labeling results. These combined results demonstrate pPDM (12-13 /Angstrom/, S S) or (2 can move minimum 10 /Angstrom/ under influence nucleotide binding. Because these are separated only nine amino acids primary sequence, small section chain must possess extraordinary flexibility. « less