title: The hydrophobic contacts between the center of the βI domain and the α1/α7 helices are crucial for the low-affinity state of integrin α4 β7.
abstract: Integrin α4 β7 mediates both rolling and firm adhesion of lymphocytes by modulating its affinity to the ligand: mucosal addressin cell adhesion molecule-1 (MAdCAM-1). Integrin activation is associated with allosteric reshaping in the β subunit I (βI) domain. A prominently conformational change comprises displacement of the α1 and α7 helices in the βI domain, suggesting that the location of these helices is important for the change in integrin affinity. In the present study, we report that the hydrophobic contacts between the center of the β7 I domain and the α1/α7 helices play critical roles in keeping α4 β7 in a low-affinity state. Using molecular dynamics simulation, we identified nine hydrophobic residues that might be involved in the critical hydrophobic contacts maintaining integrin in a low-affinity state. Integrin β7 I domain exhibited a lower binding free energy for ligand after disrupting these hydrophobic contacts by substituting the hydrophobic residues with Ala. Moreover, these α4 β7 mutants not only showed high-affinity binding to soluble MAdCAM-1, but also demonstrated firm cell adhesion to immobilized MAdCAM-1 in shear flow and enhanced the strength of the α4 β7 -MAdCAM-1 interaction. Disruption of the hydrophobic contacts also induced the active conformation of α4 β7 . Thus, the findings obtained in the present study reveal an important structural basis for the low-affinity state of integrin.
authors.affiliation: State Key Laboratory of Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.forename: Ting
authors.initials: T
authors.lastname: Fu
authors.forename: Bo
authors.initials: B
authors.lastname: Peng
authors.forename: Hao
authors.initials: H
authors.lastname: Sun
authors.forename: HuiYing
authors.initials: H
authors.lastname: Chu
authors.forename: GuoHui
authors.initials: G
authors.lastname: Li
authors.forename: JianFeng
authors.initials: J
authors.lastname: Chen
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules; D057809:HEK293 Cells; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007136:Immunoglobulins / Q000737:chemistry / Q000378:metabolism; D039441:Integrin alpha4 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D039641:Integrin beta Chains / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D009088:Mucoproteins / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D055550:Protein Stability; D017433:Protein Structure, Secondary; D013816:Thermodynamics
chemical_list: D015815:Cell Adhesion Molecules; D007136:Immunoglobulins; D039641:Integrin beta Chains; C504265:MADCAM1 protein, human; D009088:Mucoproteins; C091368:integrin beta7; D039441:Integrin alpha4
keywords: affinity; cell adhesion; hydrophobic contacts; integrin; molecular dynamic simulation