Supplemental Material for Dunn, Akpinar, and Sharma, 2020

Hummingbirds in flight exhibit the highest mass-specific metabolic rate of all vertebrates. The bioenergetic requirements associated with sustained hovering flight raise the possibility of unique amino acid substitutions that would enhance aerobic metabolism. Here, we have identified a non-conservative substitution within the mitochondria-encoded cytochrome <i>c</i> oxidase subunit I (COI) that is fixed within hummingbirds, but not among other vertebrates. This unusual change is also rare among metazoans, but can be identified in several clades with diverse life histories. We performed atomistic molecular dynamics simulations using bovine and hummingbird COI models, thereby bypassing experimental limitations imposed by the inability to modify mtDNA in a site-specific manner. Intriguingly, our findings suggest that COI amino acid position 153 (bovine numbering system) provides control over the hydration and activity of a key proton channel in COX. We discuss potential phenotypic outcomes linked to this alteration encoded by hummingbird mitochondrial genomes.<br>

飞行中的蜂鸟拥有所有脊椎动物中最高的单位质量代谢速率。与持续悬停飞行相关的生物能量需求，提示存在能够增强有氧代谢的独特氨基酸替换现象。本研究鉴定出一处位于线粒体编码的细胞色素c氧化酶亚基I（cytochrome c oxidase subunit I, COI）内的非保守替换，该替换在蜂鸟种群中固定存在，但在其他脊椎动物中并未出现。这类异常变异在后生动物中同样罕见，但可在多个具有不同生活史的演化支中被检测到。我们利用牛与蜂鸟的COI模型开展了全原子分子动力学模拟，从而规避了因无法对线粒体DNA（mitochondrial DNA, mtDNA）进行定点修饰所带来的实验限制。有趣的是，我们的研究结果表明，以牛为编号体系的COI第153位氨基酸位点，可调控细胞色素c氧化酶（cytochrome c oxidase, COX）中关键质子通道的水合状态与活性。我们还探讨了蜂鸟线粒体基因组所编码的这一变异可能带来的表型效应。