Key Laboratory of Microgravity (National Microgravity Laboratory) and Center of Biomechanics and Bioengineering, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
J Immunol. 2013 Apr 15;190(8):4371-81. doi: 10.4049/jimmunol.1201374. Epub 2013 Mar 20.
Macrophage-1 Ag (Mac-1) and lymphocyte function-associated Ag-1 (LFA-1), two β2 integrins expressed on neutrophils (PMNs), mediate PMN recruitment cascade by binding to intercellular adhesive molecule 1. Distinct functions of LFA-1-initiating PMN slow rolling and firm adhesion but Mac-1-mediating cell crawling are assumed to be governed by the differences in their binding affinities and kinetic rates. In this study, we applied an adhesion frequency approach to compare their kinetics in the quiescent and activated states using three molecular systems, constitutively expressed receptors on PMNs, wild-type and high-affinity (HA) full-length constructs transfected on 293T cells, and wild-type and HA recombinant extracellular constructs. Data indicate that the difference in binding affinity between Mac-1 and LFA-1 is on-rate dominated with slightly or moderately varied off-rate. This finding was further confirmed when both β2 integrins were activated by chemokines (fMLF or IL-8), divalent cations (Mg(2+) or Mn(2+)), or disulfide bond lockage on an HA state. Structural analyses reveal that such the kinetics difference is likely attributed to the distinct conformations at the interface of Mac-1 or LFA-1 and intercellular adhesive molecule 1. This work furthers the understandings in the kinetic differences between Mac-1 and LFA-1 and in their biological correlations with molecular activation and structural bases.
巨噬细胞-1 抗原（Mac-1）和淋巴细胞功能相关抗原-1（LFA-1），两种在中性粒细胞（PMN）上表达的β2 整合素，通过与细胞间黏附分子 1 结合，介导 PMN 募集级联反应。LFA-1 起始的 PMN 缓慢滚动和牢固黏附的不同功能，但 Mac-1 介导的细胞爬行被认为是由其结合亲和力和动力学速率的差异决定的。在这项研究中，我们应用粘附频率方法比较了三种分子系统中静息和激活状态下它们的动力学，这三种系统分别是：PMN 上组成性表达的受体、转染 293T 细胞的野生型和高亲和力（HA）全长构建体、以及野生型和 HA 重组细胞外构建体。数据表明，Mac-1 和 LFA-1 之间的结合亲和力差异主要是由结合速率决定的，而离解速率则略有或中度变化。当两种β2 整合素都被趋化因子（fMLF 或 IL-8）、二价阳离子（Mg(2+)或 Mn(2+)）或 HA 状态下的二硫键锁定激活时，这一发现得到了进一步证实。结构分析表明，这种动力学差异可能归因于 Mac-1 或 LFA-1 与细胞间黏附分子 1 界面的不同构象。这项工作进一步加深了对 Mac-1 和 LFA-1 之间动力学差异的理解，以及它们与分子激活和结构基础的生物学相关性的理解。
