Gakamsky D M, Bjorkman P J, Pecht I
Department of Immunology, Weizmann Institute of Science, Rehovot, Israel.
Biochemistry. 1996 Nov 26;35(47):14841-8. doi: 10.1021/bi961707u.
Thermodynamics and kinetics of interaction between a soluble class I MHC heterodimer composed of the H-2Kd heavy chain (H) and human beta 2microglobulin (beta 2m) with a dansylated peptide series based on residues 147-155 of influenza virus nucleoprotein sequence were studied by means of real-time fluorescence measurements. Peptide-heterodimer binding is a second-order process with specific rates practically independent of peptide structure (3-5 x 10(6) M-1 s-1). The ternary complex assembly involves a rate-limiting step of beta 2m association with H to yield an unstable heterodimer (tau < or = 5 s, 37 degrees C). Peptide binding provides a positive feedback enhancing H's affinity for beta 2m, thus stabilizing the ternary complex. The latter decays by either peptide or beta 2m dissociation. The first-order rate constants of peptide dissociation (0.5 x 10(-2))-(0.4 x 10(-3)) s-1, 37 degrees C) depend on their structures and are faster than that of beta 2m dissociation. The former process decreases the H affinity for beta 2m and induces their dissociation. This dissociation, in turn, drastically lowers H affinity for peptide. Thus, these three components produce a system which is stable as a trimer. This behavior is rationalized by the functional requirements of class I molecules: Peptide structure determines the ternary complex's lifetime, and peptide rebinding on the cell surface is rendered unlikely by the limited stability of the empty heterodimers and the very low peptide affinity of the heavy chains.
通过实时荧光测量研究了由H-2Kd重链（H）和人β2微球蛋白（β2m）组成的可溶性I类MHC异二聚体与基于流感病毒核蛋白序列第147 - 155位残基的丹磺酰化肽系列之间相互作用的热力学和动力学。肽 - 异二聚体结合是二级过程，其特定速率实际上与肽结构无关（3 - 5×10⁶ M⁻¹ s⁻¹）。三元复合物组装涉及β2m与H缔合形成不稳定异二聚体的限速步骤（τ≤5 s，37℃）。肽结合提供正反馈，增强H对β2m的亲和力，从而稳定三元复合物。后者通过肽或β2m解离而衰变。肽解离的一级速率常数（0.5×10⁻²） - （0.4×10⁻³） s⁻¹，37℃）取决于它们的结构，并且比β2m解离的速率常数更快。前一个过程降低了H对β2m的亲和力并诱导它们解离。这种解离反过来又极大地降低了H对肽的亲和力。因此，这三个组分产生了一个作为三聚体稳定的系统。I类分子的功能需求使这种行为合理化：肽结构决定三元复合物的寿命，并且由于空异二聚体的有限稳定性和重链对肽的极低亲和力，使得肽在细胞表面重新结合不太可能。
