Zhang W, Young A C, Imarai M, Nathenson S G, Sacchettini J C
Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461.
Proc Natl Acad Sci U S A. 1992 Sep 1;89(17):8403-7. doi: 10.1073/pnas.89.17.8403.
To study the structure of a homogenous major histocompatibility complex (MHC) class I molecule containing a single bound peptide, a complex of recombinant mouse H-2Kb, beta 2-microglobulin (beta 2m), and a fragment of the vesicular stomatitis virus (VSV) nuclear capsid protein, VSV-(N52-59) octapeptide (Arg-Gly-Tyr-Val-Tyr-Gln-Gly-Leu), was prepared by exploiting a high-yield bacterial expression system and in vitro cocomplex formation. The structure of mouse H-2Kb revealed its similarity to three human class I HLA molecules, consistent with the high primary sequence homology and common function of these peptide-presenting molecules. Electron density was located in the peptide-binding groove, to which a single peptide in a unique conformation was unambiguously fit. The peptide extends the length of the groove, parallel to the alpha-helices, and assumes an extended, mostly beta-strand conformation. The peptide is constrained within the groove by hydrogen bonding of its main-chain atoms and by contacts of its side chains with the H-2Kb molecule. The amino-terminal nitrogen atom of the peptide forms a hydrogen bond with the hydroxyl group of Tyr-171 of H-2Kb at one end of the groove, while the carboxyl-terminal oxygen forms a hydrogen bond with the hydroxyl group of Tyr-84 at the other end. Since the amino acids at both ends are conserved among human and mouse MHC molecules, this anchoring of each end of the peptide appears to be a general feature of peptide-MHC class I molecule binding and imposes restrictions on its length. The side chains of residues Tyr-3, Tyr-5, and Leu-8 of the VSV octapeptide fit into the interior of the H-2Kb molecule with no appreciable surface exposure, a finding in support of previous biological studies that showed the importance of these residues for binding. Thus, the basis for binding of specific peptide sequences to the MHC class I molecule is the steric restriction imposed on the peptide side chains by the architecture of the floor and sides of the groove. The side chains of Arg-1, Val-4, and Gln-6 and the main-chain of Gly-7 of the octapeptide are exposed on the surface of the complex, thus confirming their availability for T-cell receptor contact, as previously demonstrated by T-cell recognition experiments.
为了研究包含单个结合肽的同质性主要组织相容性复合体（MHC）I类分子的结构，利用高产细菌表达系统和体外共复合体形成方法，制备了重组小鼠H-2Kb、β2-微球蛋白（β2m）与水疱性口炎病毒（VSV）核衣壳蛋白片段VSV-(N52-59)八肽（精氨酸-甘氨酸-酪氨酸-缬氨酸-酪氨酸-谷氨酰胺-甘氨酸-亮氨酸）的复合体。小鼠H-2Kb的结构显示出它与三个人类I类HLA分子相似，这与这些肽呈递分子的高一级序列同源性和共同功能一致。电子密度位于肽结合槽中，一个具有独特构象的单个肽明确地与之契合。该肽平行于α螺旋延伸到槽的长度，并呈现出伸展的、主要为β链的构象。该肽通过其主链原子的氢键作用以及其侧链与H-2Kb分子的接触而被限制在槽内。肽的氨基末端氮原子在槽的一端与H-2Kb的Tyr-171羟基形成氢键，而羧基末端氧在另一端与Tyr-84羟基形成氢键。由于两端的氨基酸在人和小鼠MHC分子中都是保守的，肽两端的这种锚定似乎是肽-MHC I类分子结合的一个普遍特征，并对其长度施加限制。VSV八肽的Tyr-3、Tyr-5和Leu-8残基的侧链嵌入H-2Kb分子内部，没有明显的表面暴露，这一发现支持了先前的生物学研究，即表明这些残基对于结合的重要性。因此，特定肽序列与MHC I类分子结合的基础是由槽底部和侧面的结构对肽侧链施加的空间限制。八肽的Arg-1、Val-4和Gln-6侧链以及Gly-7的主链暴露在复合体表面，从而证实了它们可用于T细胞受体接触，正如先前T细胞识别实验所证明的那样。
