title: Is SH1-SH2-cross-linked myosin subfragment 1 a structural analog of the weakly-bound state of myosin?
abstract: Myosin subfragment 1 (S1) with SH1 (Cys(707)) and SH2 (Cys(697)) groups cross-linked by p-phenylenedimaleimide (pPDM-S1) is thought to be an analog of the weakly bound states of myosin bound to actin. The structural properties of pPDM-S1 were compared in this study to those of S1.ADP.BeF(x) and S1.ADP.AlF(4)(-), i.e., the established structural analogs of the myosin weakly bound states. To distinguish between the conformational effects of SH1-SH2 cross-linking and those due to their monofunctional modification, we used S1 with the SH1 and SH2 groups labeled with N-phenylmaleimide (NPM-S1) as a control in our experiments. The state of the nucleotide pocket was probed using a hydrophobic fluorescent dye, 3-[4-(3-phenyl-2-pyrazolin-1-yl)benzene-1-sulfonylamido]phen ylboronic acid (PPBA). Differential scanning calorimetry (DSC) was used to study the thermal stability of S1. By both methods the conformational state of pPDM-S1 was different from that of unmodified S1 in the S1.ADP.BeF(x) and S1.ADP.AlF(4)(-) complexes and closer to that of nucleotide-free S1. Moreover, BeF(x) and AlF(4)(-) binding failed to induce conformational changes in pPDM-S1 similar to those observed in unmodified S1. Surprisingly, when pPDM cross-linking was performed on S1.ADP.BeF(x) complex, ADP.BeF(x) protected to some extent the nucleotide pocket of S1 from the effects of pPDM modification. NPM-S1 behaved similarly to pPDM-S1 in our experiments. Overall, this work presents new evidence that the conformational state of pPDM-S1 is different from that of the weakly bound state analogs, S1.ADP.BeF(x) and S1.ADP.AlF(4)(-). The similar structural effects of pPDM cross-linking of SH1 and SH2 groups and their monofunctional labeling with NPM are ascribed to the inhibitory effects of these modifications on the flexibility/mobility of the SH1-SH2 helix.
authors.affiliation: Department of Chemistry and Biochemistry and Molecular Biology Institute, University of California, Los Angeles, California 90095, USA. abobkov@ucla.edu
authors.forename: A A
authors.initials: AA
authors.lastname: Bobkov
authors.forename: E
authors.initials: E
authors.lastname: Reisler
mesh_terms: D000244:Adenosine Diphosphate / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D001608:Beryllium / Q000737:chemistry; D001665:Binding Sites; D002152:Calorimetry, Differential Scanning; D003432:Cross-Linking Reagents / Q000737:chemistry*; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000737:chemistry; D005459:Fluorides / Q000737:chemistry; D008301:Maleimides / Q000737:chemistry*; D018482:Muscle, Skeletal / Q000737:chemistry; D015879:Myosin Subfragments / Q000737:chemistry* / Q000378:metabolism*; D009711:Nucleotides / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011817:Rabbits; D013438:Sulfhydryl Compounds / Q000737:chemistry
chemical_list: D003432:Cross-Linking Reagents; D005456:Fluorescent Dyes; D008301:Maleimides; D015879:Myosin Subfragments; D009711:Nucleotides; D009942:Organometallic Compounds; D013438:Sulfhydryl Compounds; C105164:adenosine diphosphate tetrafluoroaluminate; C035982:beryllium fluoride; D000244:Adenosine Diphosphate; C028525:N-phenylmaleimide; C011328:N,N'-4-phenylenedimaleimide; D001608:Beryllium; D005459:Fluorides