Beta1 integrin cytoplasmic domain regulates the constitutive conformation detected by MAb 15/7, but not the ligand-induced conformation.
The anti-integrin beta1 MAb 15/7 sometimes may be a reporter of integrin activation or ligand occupancy. However, certain beta1 tail deletions eliminate ligand binding despite inducing maximal constitutive 15/7 expression [Puzon-Mclaughlin et al. (1 996): J Biol Chem 271:16580-16585]. Here we describe beta1 tail mutations (e.g., double point mutations [D759L/F763L, F766L/E769L], or replacement of the beta1 tail by the beta5 tail) that prevent rather than induce constitutive appearance of the 15/7 epitope. Despite variable losses of constitutive 15/7 epitope, these mutants all retained a similar inducible 15/7 epitope component as seen upon incubation with GRGDSP peptide ligand. In addition, constitutive 15/7 expression did not correlate with integrin localization into focal adhesions. In conclusion, we show for the first time for a fully functional integrin that specific mutations within the beta1 tail can down-regulate the constitutive appearance of an extracellular conformation defined by MAb 15/7. Because this regulation occurs away from the ligand binding site and does not correlate with responsiveness to integrin ligand, cell adhesion, or localization into focal adhesions, a novel type of conformational regulation is suggested.
Crommie
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Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA.
Hemler
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ME
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism*; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism*; D006801:Humans; D019012:Integrin beta1 / Q000737:chemistry* / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D017354:Point Mutation; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism
D000911:Antibodies, Monoclonal; D019012:Integrin beta1; D011994:Recombinant Proteins