Regulation of Conformation and Ligand Binding Function of Integrin α5β1 by the β1 Cytoplasmic Domain

doi:10.1074/jbc.271.28.16580

Regulation of Conformation and Ligand Binding Function of Integrin α5β1 by the β1 Cytoplasmic Domain*

From the^‡ Department of Vascular Biology, The Scripps Research Institute, La Jolla, California 92037 and
^§ Athena Neurosciences, South San Francisco, California 94080

^¶ To whom correspondence should be addressed:
Dept. of Vascular Biology, Scripps Research Inst., VB-1, 10666 North Torrey Pines Rd., La Jolla, CA 92037.
Tel.: 619-784-7122; Fax: 619-784-7323; E-mail: takada{at}scripps.edu

Abstract

We have studied the role of the cytoplasmic domain in the conformation and affinity modulation of the integrin β1. Expression of a conformation-dependent anti-β1 antibody 15/7 correlates with activation in wild-type β1. Truncation of 16 carboxyl-terminal residues in the cytoplasmic domain (the 762t β1 mutant) induces constitutive expression of the 15/7 epitope at a high level (which probably reflects a major conformational change of the extracellular domain) but does not activate ligand binding. The dissociation of epitope expression and affinity suggests that the epitope expression reflects the conformation of nonligand binding sites of the extracellular domain of β1 but does not necessarily reflect that of the ligand binding sites. Indeed we discovered that the 15/7 epitope is in fact located in the nonligand binding region of β1 (within residues 354-425). The 762t mutant has apparently normal α/β association, suggesting that the overexpression of the 15/7 epitope is not due to α/β dissociation. The data suggest that the carboxyl-terminal 16 residues of the β1 cytoplasmic domain are critical for properly modulating conformation and affinity of β1 integrins.

Footnotes

↵* This work was supported by National Institute of Health Grants GM47157 and GM49899. This is Publication 9110-VB from The Scripps Research Institute. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

mAb

monoclonal antibody

FITC

fluorescein isothiocyanate

Fn

fibronectin

DMEM

Dulbecco's modified Eagle's medium

wt

wild-type

CHO

Chinese hamster ovary

PBS

phosphate-buffered saline.
- Received March 15, 1996.