Sructural study of the M4 Immune Evasion Protein

溶液NMR是用于不超过200-300个氨基酸残基的蛋白质和蛋白质复合物的结构表征的有力工具，但是难以获得大量正确重折叠的、同位素富集的蛋白质使得这种方法对于m04蛋白质具有挑战性。 然而，我们已经能够获得几乎完整的骨架共振分配，以及有限的酰胺-酰胺NOE数据，该系统。在建模技术的最新进展，原则上使用程序罗塞塔，使人们有可能模拟的基础上，这种化学位移和有限的NOE信息的蛋白质的结构。 Rosetta隐含的物理上真实的能量函数可以区分天然和非天然蛋白质构象，化学位移和NOE信息大大减少了构象空间的允许区域。已经从这种方法中得到了m04的精细模型，揭示了与常见的IgG折叠大致相似的结构，但具有许多新的元素。 基于序列同源性，新结构被认为是m02-m06蛋白家族所有成员的代表。 m06蛋白确实被发现在结构上与m04同源，但是以与m04明显不同的方式与MHC-I接合，并且似乎与β-微球蛋白的结合竞争。

Solution NMR is a powerful tool for structural characterization of proteins and protein complexes not exceeding 200-300 amino acid residues, but difficulties in obtaining large quantities of properly refolded, isotopically enriched protein make this approach challenging for the m04 protein. However, we have been able to obtain virtually complete backbone resonance assignments as well as limited amide-amide NOE data for this system. Recent advances in modeling techniques using the program Rosetta in principle make it possible to model the structure of the protein on the basis of this chemical shift and limited NOE information. The physically realistic energy function implicit to Rosetta can discriminate native from non-native protein conformations and the chemical shift and NOE information strongly reduce the permissible region of conformational space. Refined models for m04 have been derived from this approach, revealing a structure that is roughly similar to the common Igg fold, but with numerous novel elements. Based on sequence homology, the new structure is believed to be representative of all members of the m02-m06 protein family. The m06 protein indeed is found to be structurally homologus to m04, but engages with the MHC-I in a manner that is distinctly different from m04, and appears in competition with binding of beta-microglobulin.