| Autor: |
Nicklisch SC; Marine Science Institute and Department of Molecular, Cell & Developmental Biology, University of California , Santa Barbara, California 93106, United States., Spahn JE; Marine Science Institute and Department of Molecular, Cell & Developmental Biology, University of California , Santa Barbara, California 93106, United States., Zhou H; Department of Chemistry and Biochemistry, University of California , Santa Barbara, California 93106, United States., Gruian CM; Institute of Interdisciplinary Research in Bio-Nano-Sciences, Babeş-Bolyai University , Cluj-Napoca 400084, Romania., Waite JH; Marine Science Institute and Department of Molecular, Cell & Developmental Biology, University of California , Santa Barbara, California 93106, United States. |
| Abstrakt: |
Adhesive mussel foot proteins (Mfps) rely in part on DOPA (3,4-dihydroxyphenyl-l-alanine) side chains to mediate attachment to mineral surfaces underwater. Oxidation of DOPA to Dopaquinone (Q) effectively abolishes the adsorption of Mfps to these surfaces. The thiol-rich mussel foot protein-6 (Mfp-6) rescues adhesion compromised by adventitious DOPA oxidation by reducing Q back to DOPA. The redox chemistry and kinetics of foot-extracted Mfp-6 were investigated by using a nonspecific chromogenic probe to equilibrate with the redox pool. Foot-extracted Mfp-6 has a reducing capacity of ~17 e(-) per protein; half of this comes from the cysteine residues, whereas the other half comes from other constituents, probably a cohort of four or five nonadhesive, redox-active DOPA residues in Mfp-6 with an anodic peak potential ~500 mV lower than that for oxidation of cysteine to cystine. At higher pH, DOPA redox reversibility is lost possibly due to Q scavenging by Cys thiolates. Analysis by one- and two-dimensional proton nuclear magnetic resonance identified a pronounced β-sheet structure with a hydrophobic core in foot-extracted Mfp-6 protein. The structure endows redox-active side chains in Mfp-6, i.e., cysteine and DOPA, with significant reducing power over a broad pH range, and this power is measurably diminished in recombinant Mfp-6. |
