Molecular Basis for Interaction between Icap1α PTB Domain and β1 Integrin

Bao Q Hoang,Jenny Liu,Timothy A Springer,David D Chang

doi:10.1074/jbc.m109031200

Abstract

Icap1 alpha is a 200-amino acid protein that binds to the COOH-terminal 13 amino acids ((786)AVTTVVNPKYEGK(798)) of the integrin beta(1) subunit. Alanine scanning mutagenesis of this region revealed that Val(787), Val(790), and (792)NPKY(795) are critical for Icap1 alpha binding. The NPXY motif is a known binding substrate for phosphotyrosine binding (PTB) domain proteins. The sequences of Icap1 alpha, residues 58--200, and the beta(1) integrin, residues 786-797, were aligned to the available PTB-peptide structures to generate a high quality structural model. Site-directed mutagenesis showed that Leu(135), Ile(138), and Ile(139) of Icap1 alpha, residues predicted by the model to be in close proximity to (792)NPKY(795), and Leu(82) and Tyr(144), residues expected to form a hydrophobic pocket near Val(787), are required for the Icap1 alpha-beta(1) integrin interaction. These findings indicate that Icap1 alpha is a PTB domain protein, which recognizes the NPXY motif of beta(1) integrin. Furthermore, our date suggest that an interaction between Val(787) and the hydrophobic pocket created by Leu(82) and Tyr(144) of Icap1 alpha forms the basis for the specificity of Icap1 alpha for the beta(1) integrin subunit.

Highlights

Icap1␣ is a 200-amino acid protein that binds to the COOH-terminal 13 amino acids (786AVTTVVNPKYEGK798) of the integrin ␤1 subunit
Site-directed mutagenesis showed that Leu135, Ile138, and Ile139 of Icap1␣, residues predicted by the model to be in close proximity to 792NPKY795, and Leu82 and Tyr144, residues expected to form a hydrophobic pocket near Val787, are required for the Icap1␣-␤1 integrin interaction
These findings indicate that Icap1␣ is a phosphotyrosine binding (PTB) domain protein, which recognizes the NPXY motif of ␤1 integrin

Summary

Introduction

Icap1␣ is a 200-amino acid protein that binds to the COOH-terminal 13 amino acids (786AVTTVVNPKYEGK798) of the integrin ␤1 subunit. The sequences of Icap1␣, residues 58 –200, and the ␤1 integrin, residues 786 –797, were aligned to the available PTB-peptide structures to generate a high quality structural model. These findings indicate that Icap1␣ is a PTB domain protein, which recognizes the NPXY motif of ␤1 integrin.

Results

Conclusion