Alteration of the α1β2/α2β1 subunit interface contributes to the increased hemoglobin-oxygen affinity of high-altitude deer mice.

Noriko Inoguchi,Takashi Kumasaka,Hideaki Moriyama,Chandrasekhar Natarajan,Jay F Storz,Seiki Baba,Nobuhiro Mizuno

doi:10.1371/journal.pone.0174921

Abstract

BackgroundDeer mice (Peromyscus maniculatus) that are native to high altitudes in the Rocky Mountains have evolved hemoglobins with an increased oxygen-binding affinity relative to those of lowland conspecifics. To elucidate the molecular mechanisms responsible for the evolved increase in hemoglobin-oxygen affinity, the crystal structure of the highland hemoglobin variant was solved and compared with the previously reported structure for the lowland variant.ResultsHighland hemoglobin yielded at least two crystal types, in which the longest axes were 507 and 230 Å. Using the smaller unit cell crystal, the structure was solved at 2.2 Å resolution. The asymmetric unit contained two tetrameric hemoglobin molecules.ConclusionsThe analyses revealed that αPro50 in the highland hemoglobin variant promoted a stable interaction between αHis45 and heme that was not seen in the αHis50 lowland variant. The αPro50 mutation also altered the nature of atomic contacts at the α1β2/α2β1 intersubunit interfaces. These results demonstrate how affinity-altering changes in intersubunit interactions can be produced by mutations at structurally remote sites.

Highlights

Hemoglobin is a heterotetrameric protein consisting of two α subunits and two β subunits, and each subunit has an iron-centered heme that reversibly binds oxygen [1]
Studies of structure-function relationships in hemoglobin have focused on heme-ligand binding at the active site [4, 5] as well as the oxygenation-linked conformational changes between the R and the tense state (T state) [6,7,8]
The highland hemoglobin variant had a reduced intersubunit contact surface, at the α1β2/α2β1 switch region. These analyses suggest that the loose intersubunit interfaces in the highland hemoglobin molecule confers a flexible structure that shifts the allosteric equilibrium towards the relaxed state (R state) by lowering the free energy of the R$T transition, thereby increasing oxygen affinity

Summary

Background

Russian Academy of Medical Sciences, RUSSIAN FEDERATION. Deer mice (Peromyscus maniculatus) that are native to high altitudes in the Rocky Mountains have evolved hemoglobins with an increased oxygen-binding affinity relative to those of lowland conspecifics. To elucidate the molecular mechanisms responsible for the evolved increase in hemoglobin-oxygen affinity, the crystal structure of the highland hemoglobin variant was solved and compared with the previously reported structure for the lowland variant

Conclusions

Introduction

Materials and methods

Discussion