Solution properties of tetramethylrhodamine-modified G-actin |
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| Authors: | Kudryashov Dmitry S Reisler Emil |
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| Affiliation: | Department of Chemistry and Biochemistry and the Molecular Biology Institute, University of California, Los Angeles, California 90095 USA. |
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| Abstract: | In the recently solved structure of TMR-modified ADP-G-actin, the nucleotide cleft is in a closed state conformation, and the D-loop contains an alpha-helix (L. R. Otterbein, P. Graceffa, and R. Dominguez, 2001, Science, 293:708-711). Subsequently, questions were raised regarding the possible role of the TMR label on Cys(374) in determining these aspects of G-actin structure. We show here that the susceptibility of D-loop on G-actin to subtilisin cleavage, and ATP/ADP-dependent changes in this cleavage, are not affected by TMR-labeling of actin. The TMR modification inhibits nucleotide exchange, but has no effect on DNase I binding and the fast phase of tryptic digestion of actin. These results show an absence of allosteric effects of TMR on subdomain 2, while confirming ATP/ADP-dependent changes in D-loop structure. In conjunction with similar results obtained on actin-gelsolin segment 1 complex, this works reveals the limitations of solution methods in probing the putative open and closed nucleotide cleft states of G-actin. |
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| Keywords: | DTT, dithiothreitol D-loop, DNase I-binding loop ?-ADP, 1,N,6-ethenoadenosine 5′-diphosphate ?-ATP, 1,N,6-ethenoadenosine 5′-triphosphate gelsolin-S1, gelsolin segment 1 SDS-PAGE, sodium dodecylsulphate polyacrylamide gel electrophoresis TMR, tetramethylrhodamine-5-maleimide |
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