338회 β-2 Integrin: Structure-Function and Activation Analyses

338회

연사 :  남 상 욱, 강원대학교 사범대학 과학교육학부

제목: β-2 Integrin: Structure-Function and Activation Analyses

Abstract

 Integrins are the transmembrane proteins which link signals from extracellular matrix to internal cytoskeleton. The β2 integrins on leukocytes play important roles on cell-cell or cell-matrix adhesion through their ability to bind multiple ligands. The α subunits of leukocyte β2 integrins contain an approximately 200 amino acid inserted domain (I-domain) which is implicated in ligand binding function. To understand the characteristics of ligand binding to α subunit of β2 integrin, a recombinant form of I-domain of α X was generated and analyzed for the interaction with fibrinogen, one of the ligands. It was found that CD11c I-domain bound fibrinogen specifically. Divalent cations such as Mg2+ and Mn2+, were required for fibrinogen binding to CD11c I-domain.  The I domains of CD11 have a unique structure with 6-7 α helixes and 6 β sheets with interconnecting loops.  A structure and functional analysis revealed that the loops on the top of CD11c I domain such as loop βA-α1, α3-α4, βD-α5 and βF-α7 are involved in fibrinogen binding, and two loops (α3-α4 and βD-α5) are more important than others for the recognition of fibrinogen. This integrin is activated to bind its ligands by signals derived from inside of cells and the activation is consisted of two distinct processes. The one is so called avidity change in which each integrin forms clusters by cytoskeleton rearrangement. The other process is the affinity change, which refers the process of conformational changes resulting in high affinity to its ligand. To understand how integrin activation processes are interlinked and how these affinity and avidity changes trigger several signaling pathways, cDNA of αM I domain was cloned and point mutations were introduced to make internal -S-S- bonds which create high affinity (open locked, OL)or low affinity (closed locked, CL)of I domain. The binding properties of OL or CL I domain revealed that the dissociation constant of OL was 20 times higher than that of wild type. Transfection of cells with OL or CL is currently carried out for analyzing signals of β2 integrin.  The resulting cells provide useful tools to dissect signals related the cell adhesion, migration and cytokine gene expression in leukocytes.