Distinct Acidic Clusters and Hydrophobic Residues in the Alternative Splice Domains X1 and X2 of α7 Integrins Define Specificity for Laminin Isoforms

详细信息    查看全文

• 作者：Helga von der Mark ; Ernst Pö ; schl ; Harald Lanig ; Takako Sasaki ; Rainer Deutzman ; Klaus von der Mark
• 关键词：Alpha7 integrin ; X1 ; X2 splice variants ; laminin isoforms ; homology modeling ; molecular dynamics simulation
• 刊名：Journal of Molecular Biology
• 出版年：2007
• 出版时间：31 August 2007
• 年：2007
• 卷：371
• 期：5
• 页码：1188-1203
• 全文大小：1412 K

文摘

The binding specificity of α7β1 integrins for different laminin isoforms is defined by the X1 and X2 splice domains located in the beta-propeller domain of the α7 subunit. In order to gain insight into the mechanism of specific laminin–integrin interactions, we defined laminin-binding epitopes of the α7X1 and -X2 domains by single amino acid substitutions and domain swapping between X1 and X2. The interaction of mutated, recombinantly prepared α7X1β1 and α7X2β1 heterodimers with various laminin isoforms was studied by surface plasmon resonance and solid phase binding assays. The data show that distinct clusters of surface-exposed acidic residues located in different positions of the X1 and the X2 loops are responsible for the specific recognition of laminins. These residues are conserved between the respective X1 or X2 splice domains of the α7 chains of different species, some also in the corresponding X1/X2 splice domains of α6 integrin. Interestingly, ligand binding was also modulated by mutating surface-exposed hydrophobic residues (α7X1L205, α7X2Y208) at positions corresponding to the fibronectin binding synergy site in α5β1 integrin. Mutations in X1 that affected binding to laminin-1 also affected binding to laminin-8 and -10, but not to the same extent, thus allowing conclusions on the specific role of individual surface epitopes in the selective recognition of laminin-1 versus laminins -8 and -10. The role of the identified epitopes was confirmed by molecular dynamics simulations of wild-type integrins and several inactivating mutations. The analysis of laminin isoform interactions with various X1/X2 chimaera lend further support to the key role of negative surface charges and pointed to an essential contribution of the N-terminal TARVEL sequence of the X1 domain for recognition of laminin-8 and -10. In conclusion, specific surface epitopes containing charged and hydrophobic residues are essential for ligand binding and define specific interactions with laminin isoforms.