Mitochondrial and microsomal ferric b5 cytochromes exhibit divergent conformational plasticity in the context of a common fold.
Native-state hydrogen-deuterium exchange (HDX) monitored by NMR spectroscopy has been used to compare conformational plasticity in ferric rat liver outer mitochondrial membrane cytochrome b5 (rOM b5) and ferric bovine liver microsomal cytochrome b5 (bMc b5). Analysis of the data indicated that rOM b5 is the less conformationally flexible protein on the time scale probed by the HDX experiments. The data also suggest a likely contributor to the much higher kinetic barrier for the release of hemin from OM b5s in comparison to Mc b5s, a characteristic that may be to a large extent the source of their divergent functional properties. Specifically, the data indicate that conformational mobility within helices alpha4 and alpha5, which flank the loop harboring axial ligand His63, is considerably more restricted in rOM b5 than in bMc b5. The lower conformational flexibility of alpha4 and alpha5 in rOM b5 can reasonably be attributed to more extensive hydrophobic packing in that region of the protein, arising from two conserved side chain packing motifs in OM cytochrome b5s [Altuve, A., Wang, L., Benson, D. R., and Rivera, M. (2004) Biochem. Biophys. Res. Commun. 314, 602-609].
Simeonov
Mario
M
Department of Chemistry, The University of Kansas, 1251 Wescoe Hall Drive, Lawrence, Kansas 66045-7582, USA.
Altuve
Adriana
A
Massiah
Michael A
MA
Wang
An
A
Eastman
Margaret A
MA
Benson
David R
DR
Rivera
Mario
M
D000595:Amino Acid Sequence; D000818:Animals; D015786:Cytochromes b5 / Q000737:chemistry*; D008862:Microsomes, Liver / Q000201:enzymology*; D008930:Mitochondria, Liver / Q000201:enzymology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017510:Protein Folding; D017433:Protein Structure, Secondary; D051381:Rats; D017386:Sequence Homology, Amino Acid; D013816:Thermodynamics
D015786:Cytochromes b5