title: Distinct binding affinities of Mac-1 and LFA-1 in neutrophil activation.
abstract: 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.
authors.affiliation: Key Laboratory of Microgravity (National Microgravity Laboratory) and Center of Biomechanics and Bioengineering, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Ning
authors.initials: N
authors.lastname: Li
authors.forename: Debin
authors.initials: D
authors.lastname: Mao
authors.forename: Shouqin
authors.initials: S
authors.lastname: Lü
authors.forename: Chunfang
authors.initials: C
authors.lastname: Tong
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Mian
authors.initials: M
authors.lastname: Long
mesh_terms: D057809:HEK293 Cells; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D007700:Kinetics; D016169:Lymphocyte Function-Associated Antigen-1 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D016177:Macrophage-1 Antigen / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D018375:Neutrophil Activation / Q000276:immunology*; D011485:Protein Binding / Q000276:immunology; D025941:Protein Interaction Mapping; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D014162:Transfection
chemical_list: D016169:Lymphocyte Function-Associated Antigen-1; D016177:Macrophage-1 Antigen; D011994:Recombinant Proteins; D018799:Intercellular Adhesion Molecule-1