MYOSIN SUBFRAGMENT-1 HYDROPHOBICITY CHANGES ASSOCIATED WITH DIFFERENTNUCLEOTIDE-INDUCED CONFORMATIONS

Myosin subfragment 1 hydrophobicity was found to be sensitive to the o ccupancy and nature of bound nucleotide at its active site, as shown b y changes in elution behavior of unmodified and chemically modified S1 during phenyl hydrophobic chromatography. The elution properties of S 1 were unaltered by alkylation of SH1 (Cys-707) with N-ethylmaleimide or by covalent bridging between SH1 and SH2 (Cys-697) with p-phenylene dimaleimide with trapping of MgBDP. Although addition of MgADP or MgAT P to the elution buffers had minimal effect on the elution properties of these modified S1 species, the presence of these nucleotides was fo und to produce differential effects with unmodified S1. With MgADP, wh ere S1 is in the S1MgADP state, the elution times were decreased slig htly, whereas with MgATP, where S1 is primarily in the S1*MgADP . P-i state, the elution times were significantly lowered, indicating reduc ed accessibility for the immobilized phenyl ligand. Stable S1 ternary complexes, formed with MgADP and various P-i analogues, showed elution times similar to that for S1 in the buffers containing MgATP. Thus, t wo main classes of nucleotide-induced S1 conformations can be defined according to their interaction with immobilized phenyl. These nucleoti de-induced changes in S1 hydrophobicity correlate well with reported c hanges in radius of gyration of S1 associated with different states of the bound nucleotide [Wakabayashi, K., Tokunga, M., Kohno, I., Sugimo to, Y.; Hamanaka, T., Takezawa, Y., Wakabayashi, T., & Amemiya, Y. (19 92) Science 258, 443-447], suggesting that the observed hydrophobicity interaction may be measuring accessibility of the immobilized phenyl ligand into a hydrophobic crevice, and that this crevice is closed or tightened when S1 is in the S1*MgADP . P-i state.