(The FASEB Journal. 2007;21:790.1)
© 2007 FASEB
Steady state and kinetic CD studies of metal binding by methanobactin
Vinay Rao1,
Lori Scardino1,
Lee Behling1,
Scott Hartsel1,
Marcus Mc Ellistrem1 and
Alan Dispirito2
1 Chemistry, University of Wisconsin-Eau Claire, Phillips Hall, Chemistry, Eau Claire, WI, 54702,
2 Biochemistry, Iowa State University, 205 Science I, Iowa State University, Ames, IA, 50011
ABSTRACT
Methanobactin (mb) is a chalkophore produced by Methylosinus trichosporium OB3b. Mb has been shown to bind to many metals in addition to Cu(II) and Cu(I). There seem to be two general families of CD spectra associated with different types of metals. The first is common to soft metal ions and includes Au(III), Cu(II), Pb(II), Ag(I), and Hg(II). The second is common to hard metal ions and includes Zn(II), Mn(II), Co(II), and Ni(II). All metals can be displaced by Cu(II) except for Au(III), Cu(I), and Ag(I) which seem to inactivate mb, possibly irreversibly. This may be because mb is known to reduce Cu(II), Au(III), and Ag(I), and the oxidation of mb may impair subsequent metal binding. Alternatively, Pb(II) and all other metals on this list, can be displaced by Cu(II) suggesting that they cannot be reduced. Kinetic CD spectra of immediate and long-term changes in mb may be indicative of metal-reduction processes or changes in ligand binding and aggregation state. We find that most metals bind more rapidly than the dead time of the instrument (~10 msec) and lead to stable conformations, but Au(III) and Cu(II) show longer-term changes that may be associated with oxidation and/or alteration of mb ligands.
