Evolution of Cytochrome c Oxidase in Hypoxia Tolerant Sculpins (Cottidae, Actinopterygii)

摘要

Vertebrate hypoxia tolerance can emerge from modifications to the oxygen (O 2 ) transport cascade, but whether there is adaptive variation to O 2 binding at the terminus of this cascade, mitochondrial cytochrome c oxidase (COX), is not known. In order to address the hypothesis that hypoxia tolerance is associated with enhanced O 2 binding by mitochondria we undertook a comparative analysis of COX O 2 kinetics across species of intertidal sculpins (Cottidae, Actinopterygii) that vary in hypoxia tolerance. Our analysis revealed a significant relationship between hypoxia tolerance (critical O 2 tension of O 2 consumption rate; P crit ), mitochondrial O 2 binding affinity (O 2 tension at which mitochondrial respiration was half maximal; P 50 ), and COX O 2 -binding affinity (apparent Michaelis–Menten constant for O 2 binding to COX; K m,app O 2 ). The more hypoxia tolerant species had both a lower mitochondrial P 50 and lower COX K m,app O 2 , facilitating the maintenance of mitochondrial function to a lower O 2 tension than in hypoxia intolerant species. Additionally, hypoxia tolerant species had a lower overall COX V max but higher mitochondrial COX respiration rate when expressed relative to maximal electron transport system respiration rate. In silico analyses of the COX3 subunit postulated as the entry point for O 2 into the COX protein catalytic core, points to variation in COX3 protein stability (estimated as free energy of unfolding) contributing to the variation in COX K m,app O 2 . We propose that interactions between COX3 and cardiolipin at four amino acid positions along the same alpha-helix forming the COX3 v-cleft represent likely determinants of interspecific differences in COX K m,app O 2 .