GSBS Student Publications

Title

Mutation of residue Phe97 to Leu disrupts the central allosteric pathway in Scapharca dimeric hemoglobin

UMMS Affiliation

Graduate School of Biomedical Sciences; Program in Molecular Medicine and Department of Biochemistry and Molecular Biology

Date

5-16-1997

Document Type

Article

Medical Subject Headings

Allosteric Regulation; Animals; Bivalvia; Escherichia coli; Hemoglobins; Molecular Sequence Data; Oxygen; Phenylalanine; Point Mutation; Protein Folding

Disciplines

Life Sciences | Medicine and Health Sciences

Abstract

Residue Phe97, which is thought to play a central role in the cooperative functioning of Scapharca dimeric hemoglobin, has been mutated to leucine to test its proposed role in mediating cooperative oxygen binding. This results in an 8-fold increase in oxygen affinity and a marked decrease in cooperativity. Kinetic measurements of ligand binding to the Leu97 mutant suggest an altered unliganded (deoxy) state, which has been confirmed by high resolution crystal structures in the unliganded and carbon monoxide-liganded states. Analysis of the structures at allosteric end points reveals them to be remarkably similar to the corresponding wild-type structures, with differences confined to the disposition of residue 97 side chain, F-helix geometry, and the interface water structure. Increased oxygen affinity results from the absence of the Phe97 side chain, whose tight packing in the heme pocket of the deoxy state normally restricts the heme from assuming a high affinity conformation. The absence of the Phe97 side chain is also associated with diminished cooperativity, since Leu97 packs in the heme pocket in both states. Residual cooperativity appears to be coupled with observed structural transitions and suggests that parallel pathways for communication exist in Scapharca dimeric hemoglobin.

Rights and Permissions

Citation: J Biol Chem. 1997 May 16;272(20):13171-9.

Related Resources

Link to article in PubMed

Journal Title

The Journal of biological chemistry

PubMed ID

9148933