PDBsum entry 2spm

Oxygen storage

PDB id: 2spm

Contents

Protein chain

154 a.a. *

Ligands

SO4

HEM

Waters ×113

* Residue conservation analysis

PDB id:

2spm

Name:

Oxygen storage

Title:

A novel site-directed mutant of myoglobin with an unusually high o2 affinity and low autooxidation rate

Structure:

Myoglobin. Chain: a. Engineered: yes

Source:

Physeter catodon. Sperm whale. Organism_taxid: 9755

Biol. unit:

Hexamer (from PQS)

Resolution:

1.70Å R-factor: 0.167

Authors:

M.L.Quillin,R.M.Arduini,G.N.Phillips Jr.

Key ref:

T.E.Carver et al. (1992). A novel site-directed mutant of myoglobin with an unusually high O2 affinity and low autooxidation rate. J Biol Chem, 267, 14443-14450. PubMed id: 1629229

Date:

25-Aug-93 Release date: 31-Jan-94

Protein chain

P02185  (MYG_PHYMC) -  Myoglobin from Physeter macrocephalus

Seq: 154 a.a.

Struc: 154 a.a.*

* PDB and UniProt seqs differ at 2 residue positions (black crosses)

Enzyme reactions

• Enzyme class: E.C.?

J Biol Chem 267:14443-14450 (1992)

PubMed id: 1629229

A novel site-directed mutant of myoglobin with an unusually high O2 affinity and low autooxidation rate.

T.E.Carver, R.E.Brantley, E.W.Singleton, R.M.Arduini, M.L.Quillin, G.N.Phillips, J.S.Olson.

ABSTRACT

Mutants of sperm whale myoglobin were constructed at position 29 (B10 in helix notation) to examine the effects of distal pocket size on the rates of ligand binding and autooxidation. Leu29 was replaced with Ala, Val, and Phe using the synthetic gene and Escherichia coli expression system of Springer and Sligar (Springer, B. A., and Sligar, S. G. (1987) Proc. Natl. Acad. Sci. U. S. A. 84, 8961-8965). Structures of the ferric forms of Val29 and Phe29, and the oxy form of Phe29 myoglobin were determined to 1.7 A by x-ray crystallography. The ferric mutant proteins are remarkably isomorphous with the wild type protein except in the immediate vicinity of residue 29. Thus, the protein structure in the distal pocket of myoglobin can accommodate either a large "hole" (i.e. Ala or Val) or a large side chain (i.e. Phe) at position 29 without perturbation of tertiary structure. Phe29 oxymyoglobin is also identical to the native oxy protein in terms of overall structure and interactions between the bound O2 and His64, Val68, Phe43, and Ile107. The distance between the nearest side chain atom of residue 29 and the second atom of the bound oxygen molecule is 3.2 A in the Phe29 protein and 4.9 A in native myoglobin. The equilibrium constants for O2 binding to Ala29, Val29, and Leu29 (native) myoglobin are the same, approximately 1.0 x 10(6) M-1 at 20 degrees C, whereas that for the Phe29 protein is markedly greater, 15 x 10(6) M-1. This increase in affinity is due primarily to a 10-fold decrease in the O2 dissociation rate constant for the Phe29 mutant and appears to be the result of stabilizing interactions between the negative portion of the bound O2 dipole and the partially positive edge of the phenyl ring. Increasing the size of residue 29 causes large decreases in the rate of autooxidation of myoglobin: k(ox) = 0.24, 0.23, 0.055, and 0.005 h-1 for Ala29, Val29, Leu29 (native), and Phe29 myoglobin, respectively, in air at 37 degrees C. Thus, the Leu29----Phe mutation produces a reduced protein that is remarkably stable and is expressed in E. coli as 100% MbO2. The selective pressure to conserve Leu29 at the B10 position probably represents a compromise between reducing the rate of autooxidation and maintaining a large enough O2 dissociation rate constant to allow rapid oxygen release during respiration.