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RISS 인기검색어
- 검색키워드
- 저자 : Nitao, Lisa Kaori (검색결과 1 건)
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Conformational states of the SH1-SH2 helix in myosin
Nitao, Lisa Kaori University of California, Los Angeles 2002 해외박사(DDOD)
Muscle contraction occurs as a result of the cyclic interactions between actin, myosin, and ATP. Myosin, the molecular motor, utilizes the chemical energy from ATP to generate the force necessary for movement. The lever arm hypothesis suggest that during ATP hydrolysis, the myosin head (S1) undergoes conformational changes in its catalytic domain, leading to the swinging of the lever arm. In this dissertation, our investigations focused on a region of S1 that has been proposed to undergo such conformational changes, the cc-helix containing the reactive sulfhydryl groups, SH1 (Cys707) and SH2 (Cys697). In our studies, cross-linking reagents spanning from 7 to 17 Å were used to probe SH1-SH2 helix dynamics. Cross-linking rates were shown to depend on both the ligand-bound state of myosin and the cross-linking span. In the presence of the nucleotide analogs, MgADP, MgATPγS and MgADP.BeF<sub> x</sub>, cross-linking rates were increased only a few-fold for the shortest reagent (∼7–10Å), while the rate increases were much greater (∼40–270-fold) for the longer reagents (∼10–17 Å). For the MgADP.AlF<sub>4</sub><super>−</super> and MgADP.V<sub>i</sub>-bound states, the cross-linking rates increased at least 20-fold for all the reagents, suggesting a flexible SH1-SH2 helix. In the presence of actin, cross-linking was inhibited, indicating a stabilization of the helix. Although MgADP alone increased the rate of S1 cross-linking, in the ternary complex, acto-S1.MgADP, the SH1-SH2 helix was also found to be stable. Because a collapse of the SH1-SH2 helix is observed in the crystal structure of scallop S1.ADP, the dynamics of the SH1-SH2 helix in this S1 were also examined. The rate of scallop S1 modification by monofunctional reagents was increased by nucleotides and inhibited by actin. Mass spectrometric analysis of modified scallop S1 revealed that SH2 is more reactive than SH1. Furthermore, cross-linking results indicated that MgADP and MgATPγS induced a greater destabilization of the SH1-SH2 helix in scallop than in skeletal S1. The greater nucleotide-induced destabilization of the SH1-SH2 helix in scallop S1 correlates with the disorder of this helix in the crystal structure of scallop S1.ADP but not in the structures of other isoforms of S1. These results also reveal isoform-dependent differences in the dynamic properties of the SH1-SH2 helix in myosin.
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