Terrell James Ross, Gumpper Ryan H, Luo Ming
Department of Chemistry, Georgia State University, Atlanta, GA 30302, USA; Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, GA 30302, USA.
Department of Chemistry, Georgia State University, Atlanta, GA 30302, USA; Molecular Basis of Disease, Georgia State University, Atlanta, GA 30302, USA.
Biochem Biophys Res Commun. 2018 Jan 8;495(2):1858-1863. doi: 10.1016/j.bbrc.2017.12.038. Epub 2017 Dec 12.
Human hemoglobin (HbA) transports molecular oxygen (O) from the lung to tissues where the partial pressure of O is lower. O binds to HbA at the heme cofactor and is stabilized by a distal histidine (HisE7). HisE7 has been observed to occupy opened and closed conformations, and is postulated to act as a gate controlling the binding/release of O. However, it has been suggested that HbA also contains intraprotein oxygen channels for entrances/exits far from the heme. In this study, we developed a novel method of crystal immersion in liquid oxygen prior to X-ray data collection. In the crystals immersed in liquid oxygen, the heme center was oxidized to generate aquomethemoglobin. Increases of structural flexibility were also observed in regions that are synonymous with previously postulated oxygen channels. These regions also correspond to medically relevant mutations which affect O affinity. The way HbA utilizes these O channels could have a profound impact on understanding the relationship of HbA O transport within these disease conditions. Finally, the liquid oxygen immersion technique can be utilized as a new tool to crystallographically examine proteins and protein complexes which utilize O for enzyme catalysis or transport.
人类血红蛋白（HbA）将分子氧（O）从肺部输送到氧分压较低的组织。O在血红素辅因子处与HbA结合，并通过远端组氨酸（HisE7）得以稳定。已观察到HisE7呈现开放和闭合构象，并被假定为控制O结合/释放的门控。然而，有人提出HbA还含有远离血红素的蛋白质内氧通道用于进出。在本研究中，我们开发了一种在X射线数据收集之前将晶体浸入液氧的新方法。在浸入液氧的晶体中，血红素中心被氧化生成高铁血红蛋白。在与先前假定的氧通道同义的区域也观察到结构灵活性增加。这些区域也对应于影响O亲和力的医学相关突变。HbA利用这些氧通道的方式可能对理解这些疾病状态下HbA氧运输的关系产生深远影响。最后，液氧浸入技术可作为一种新工具，用于晶体学研究利用O进行酶催化或运输的蛋白质和蛋白质复合物。
