On the importance of ribose orientation in the substrate activation of the coenzyme B12-dependent mutases

• The degree to which the corrin ring portion of coenzyme B-12 can   facilitate the H-atom-abstraction step in the glutamate mutase   (GM)-catalyzed reaction of (S)-glutamate has been investigated with   density functional theory. The crystal structure of GM identifies two   possible orientations of the ribose portion of coenzyme B-12. In one orientation (A), the OH groups of the ribose extend away from the   corrin ring, whereas in the other orientation (B) the OH groups, especially that involving O3', are instead directed towards the corrin   ring. Our calculations identify a sizable stabilization amounting to   about 30kJ mol(-1) in the transition structure (TS) complex   corresponding to orientation B (TS(B)Corlm). In the TS complex where   the ribose instead is positioned in orientation A, no such effect is   manifested. The observed stabilization in TS(B)CorIm appears to be the   result of favorable interactions involving O3' and the corrin ring,   including a C-H center dot center dot center dot O hydrogen bond. We   find that the degree of stabilization is not particularly sensitive to   the Co-C distance. Our calculations show that any potential   stabilization afforded to the H-atom-abstraction step by coenzyme B12   is sensitive to the orientation of the ribose moiety.

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Nyckelord

density functional calculations

enzymes

molecular modeling

radicals

reaction mechanisms

Chemistry

Kemi

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