Format

Send to:

Choose Destination
See comment in PubMed Commons below
J Mol Biol. 2000 Jan 14;295(2):357-74.

Structures of the flavocytochrome p-cresol methylhydroxylase and its enzyme-substrate complex: gated substrate entry and proton relays support the proposed catalytic mechanism.

Author information

  • 1Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110, USA.

Abstract

The degradation of the toxic phenol p-cresol by Pseudomonas bacteria occurs by way of the protocatechuate metabolic pathway. The first enzyme in this pathway, p-cresol methylhydroxylase (PCMH), is a flavocytochrome c. The enzyme first catalyzes the oxidation of p-cresol to p-hydroxybenzyl alcohol, utilizing one atom of oxygen derived from water, and yielding one molecule of reduced FAD. The reducing electron equivalents are then passed one at a time from the flavin cofactor to the heme cofactor by intramolecular electron transfer, and subsequently to cytochrome oxidase within the periplasmic membrane via one or more soluble electron carrier proteins. The product, p-hydroxybenzyl alcohol, can also be oxidized by PCMH to yield p-hydroxybenzaldehyde. The fully refined X-ray crystal structure of PCMH in the native state has been obtained at 2. 5 A resolution on the basis of the gene sequence. The structure of the enzyme-substrate complex has also been refined, at 2.75 A resolution, and reveals significant conformational changes in the active site upon substrate binding. The active site for substrate oxidation is deeply buried in the interior of the PCMH molecule. A route for substrate access to the site has been identified and is shown to be governed by a swinging-gate mechanism. Two possible proton transfer pathways, that may assist in activating the substrate for nucleophilic attack and in removal of protons generated during the reaction, have been revealed. Hydrogen bonding interactions between the flavoprotein and cytochrome subunits that stabilize the intramolecular complex and may contribute to the electron transfer process have been identified.

Copyright 2000 Academic Press.

PMID:
10623531
[PubMed - indexed for MEDLINE]

LinkOut - more resources

Full Text Sources

Other Literature Sources

Molecular Biology Databases

PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for Elsevier Science
    Loading ...
    Write to the Help Desk