2zax

==Overview==

Cytochrome P450cam (P450cam) binds a protoheme IX as a prosthetic group, via noncovalent interactions. Heme-6-propionate, one of the two, heme-propionate side chains, forms hydrogen-bonding interactions with, Arg112 and other hydrophilic amino acid residues. Here, we demonstrate the, structural and functional roles of the 6-propionate side chain in P450cam, using a reconstituted protein with 6-depropionate-6-methylated protoheme, IX (one-legged heme). The spectroscopic data and the enzymatic activities, reveal that removal of the 6-propionate has no clear influence on the, enzyme property. The rate of electron transfer from putidaredoxin (Pdx), a, natural redox partner, to P450cam was not significantly changed, whereas, the removal of the 6-propionate decreased the affinity of Pdx by 3.5-fold, supporting the proposed role of Arg112 as the essential constituent of the, Pdx binding site. Resonance Raman experiments indicate that removal of the, 6-propionate weakens the Fe-S bond strength. The X-ray structure of the, reconstituted protein at 1.55 A resolution is highly superimposable with, that of the wild-type protein, whereas the thiolate of the Cys357 heme, ligand in the reconstituted protein is visible from the protein surface, owing to the lack of the 6-propionate. Lengthening of the Fe-S bond and, the water accessibility could facilitate protonation of thiolate anion to, thiol, explaining the observed formation of the inactive P420 species, under the mild conditions. Therefore, the d-camphor hydroxylation reaction, requires a 6-propionate-protein matrix interaction to maintain an active, P450 species.

Evaluation of the Functional Role of the Heme-6-propionate Side Chain in Cytochrome P450cam., Harada K, Sakurai K, Ikemura K, Ogura T, Hirota S, Shimada H, Hayashi T, J Am Chem Soc. 2007 Dec 19;. PMID:[http://ispc.weizmann.ac.il//pmbin/getpm?pmid=18088124 18088124]

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