Callebaut I, Dulin F, Bertrand O, Ripoche P, Mouro I, Colin Y, Mornon J-P, Cartron J-P
Département de biologie structurale, IMPMC, CNRS UMR7590, universités Paris VI et Paris VII, case 115, 4, place Jussieu, 75252 Paris cedex 05, France.
Transfus Clin Biol. 2006 Mar-Apr;13(1-2):70-84. doi: 10.1016/j.tracli.2006.02.001. Epub 2006 Apr 3.
Rh (Rhesus) is a major blood group system in man, which is clinically significant in transfusion medicine. Rh antigens are carried by an oligomer of two major erythroid specific polypeptides, the Rh (D and CcEe) proteins and the RhAG glycoprotein, that shared a common predicted structure with 12 transmembrane a-helices (M0 to M11). Non erythroid homologues of these proteins have been identified (RhBG and RhCG), notably in diverse organs specialized in ammonia production and excretion, such as kidney, liver and intestine. Phylogenetic studies and experimental evidence have shown that these proteins belong to the Amt/Mep/Rh protein superfamily of ammonium/methylammonium permease, but another view suggests that Rh proteins might function as CO2 gas channels. Until recently no information on the structure of these proteins were available. However, in the last two years, new insight has been gained into the structural features of Rh proteins (through the determination of the crystal structures of bacterial AmtB and archeaebacterial Amt-1. Here, models of the subunit and oligomeric architecture of human Rh proteins are proposed, based on a refined alignment with and crystal structure of the bacterial ammonia transporter AmtB, a member of the Amt/Mep/Rh superfamily. This alignment was performed considering invariant structural features, which were revealed through Hydrophobic Cluster Analysis, and led to propose alternative predictions for the less conserved regions, particularly in the N-terminal sequences. The Rh models, on which an additional Rh-specific, N-terminal helix M0 was tentatively positioned, were further assessed through the consideration of biochemical and immunochemical data, as well as of stereochemical and topological constraints. These models highlighted some Rh specific features that have not yet been reported. Among these, are the prediction of some critical residues, which may play a role in the channel function, but also in the stability of the subunit structure and oligomeric assembly. These results provide a basis to further understand the structure/function relationships of Rh proteins, and the alterations occurring in variant phenotypes.
Rh（恒河猴血型）是人类主要的血型系统，在输血医学中具有临床意义。Rh抗原由两种主要的红系特异性多肽的寡聚体携带，即Rh（D和CcEe）蛋白和RhAG糖蛋白，它们具有共同的预测结构，包含12个跨膜α螺旋（M0至M11）。已鉴定出这些蛋白的非红系同源物（RhBG和RhCG），特别是在专门进行氨生成和排泄的各种器官中，如肾脏、肝脏和肠道。系统发育研究和实验证据表明，这些蛋白属于铵/甲基铵通透酶的Amt/Mep/Rh蛋白超家族，但另一种观点认为Rh蛋白可能作为二氧化碳气体通道发挥作用。直到最近，关于这些蛋白结构的信息仍然缺乏。然而，在过去两年中，通过确定细菌AmtB和古细菌Amt-1的晶体结构，人们对Rh蛋白的结构特征有了新的认识。在此，基于与细菌氨转运蛋白AmtB（Amt/Mep/Rh超家族的成员）的精细比对和晶体结构，提出了人类Rh蛋白的亚基和寡聚体结构模型。这种比对是考虑到通过疏水簇分析揭示的不变结构特征进行的，并对保守性较低的区域，特别是N端序列，提出了替代预测。通过考虑生化和免疫化学数据以及立体化学和拓扑学限制，进一步评估了Rh模型，在该模型上初步定位了一个额外的Rh特异性N端螺旋M0。这些模型突出了一些尚未报道的Rh特异性特征。其中包括对一些关键残基的预测，这些残基可能在通道功能中起作用，也可能在亚基结构和寡聚体组装的稳定性中起作用。这些结果为进一步理解Rh蛋白的结构/功能关系以及变异表型中发生的变化提供了基础。
