PDBsum entry 1cmu

Oxidoreductase (h2o2(a))

PDB id: 1cmu

Contents

Protein chain

291 a.a.

Ligands

HEM

Waters ×53

References listed in PDB file

Key reference

• Title: The role of aspartate-235 in the binding of cations to an artificial cavity at the radical site of cytochrome c peroxidase.
• Authors: M.M.Fitzgerald, M.L.Trester, G.M.Jensen, D.E.Mcree, D.B.Goodin.
• Ref.: Protein Sci, 1995, 4, 1844-1850. [DOI no: 10.1002/pro.5560040919]
• PubMed id: 8528082

Note In the PDB file this reference is annotated as "TO BE PUBLISHED". The citation details given above were identified by an automated search of PubMed on title and author names, giving a perfect match.

Abstract

The activated state of cytochrome c peroxidase, compound ES, contains a cation radical on the Trp-191 side chain. We recently reported that replacing this tryptophan with glycine creates a buried cavity at the active site that contains ordered solvent and that will specifically bind substituted imidazoles in their protonated cationic forms (Fitzgerald MM, Churchill MJ, McRee DE, Goodin DB, 1994, Biochemistry 33:3807-3818). Proposals that a nearby carboxylate, Asp-235, and competing monovalent cations should modulate the affinity of the W191G cavity for ligand binding are addressed in this study. Competitive binding titrations of the imidazolium ion to W191G as a function of [K+] show that potassium competes weakly with the binding of imidazoles. The dissociation constant observed for potassium binding (18 mM) is more than 3,000-fold higher than that for 1,2-dimethylimidazole (5.5 microM) in the absence of competing cations. Significantly, the W191G-D235N double mutant shows no evidence for binding imidazoles in their cationic or neutral forms, even though the structure of the cavity remains largely unperturbed by replacement of the carboxylate. Refined crystallographic B-values of solvent positions indicate that the weakly bound potassium in W191G is significantly depopulated in the double mutant. These results demonstrate that the buried negative charge of Asp-235 is an essential feature of the cation binding determinant and indicate that this carboxylate plays a critical role in stabilizing the formation of the Trp-191 radical cation.

Secondary reference #1

• Title: Small molecule binding to an artificially created cavity at the active site of cytochrome c peroxidase.
• Authors: M.M.Fitzgerald, M.J.Churchill, D.E.Mcree, D.B.Goodin.
• Ref.: Biochemistry, 1994, 33, 3807-3818. [DOI no: 10.1021/bi00179a004]
• PubMed id: 8142383

Secondary reference #2

• Title: The asp-His-Fe triad of cytochrome c peroxidase controls the reduction potential, Electronic structure, And coupling of the tryptophan free radical to the heme.
• Authors: D.B.Goodin, D.E.Mcree.
• Ref.: Biochemistry, 1993, 32, 3313-3324. [DOI no: 10.1021/bi00064a014]
• PubMed id: 8384877