Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan.
Biochemistry. 2023 Sep 19;62(18):2727-2737. doi: 10.1021/acs.biochem.3c00203. Epub 2023 Aug 30.
Proteins have undergone evolutionary processes to achieve optimal stability, increased functionality, and novel functions. Comparative analysis of existent and ancestral proteins provides insights into the factors that influence protein stability and function. Ancestral sequence reconstruction allows us to deduce the amino acid sequences of ancestral proteins. Here, we present the structural and functional characteristics of an ancestral protein, AncMH, reconstructed to be the last common ancestor of hemoglobins and myoglobins. Our findings reveal that AncMH harbors heme and that the heme binds oxygen. Furthermore, we demonstrate that the ferrous heme in AncMH is pentacoordinated, similar to that of human adult hemoglobin and horse myoglobin. A detailed comparison of the heme pocket structure indicates that the heme pocket in AncMH is more similar to that of hemoglobin than that of myoglobin. However, the autoxidation of AncMH is faster than that of both hemoglobin and myoglobin. Collectively, our results suggest that ancestral proteins of hemoglobins and myoglobins evolved in steps, including the hexa- to pentacoordination transition, followed by stabilization of the oxygen-bound form.
蛋白质经历了进化过程，以达到最佳的稳定性、增强的功能和新的功能。对现有和祖先蛋白质的比较分析提供了影响蛋白质稳定性和功能的因素的见解。祖先序列重建使我们能够推断出祖先蛋白质的氨基酸序列。在这里，我们展示了一个祖先蛋白质 AncMH 的结构和功能特征，它被重建为血红蛋白和肌红蛋白的最后共同祖先。我们的研究结果表明 AncMH 含有血红素，并且血红素结合氧气。此外，我们证明 AncMH 中的亚铁血红素是五配位的，类似于人成年血红蛋白和马肌红蛋白。对血红素口袋结构的详细比较表明，AncMH 的血红素口袋与血红蛋白的相似性大于肌红蛋白。然而，AncMH 的自动氧化速度比血红蛋白和肌红蛋白都快。总的来说，我们的结果表明，血红蛋白和肌红蛋白的祖先蛋白质是分步骤进化的，包括从六配位到五配位的转变，然后是氧结合形式的稳定。
