Regulation of outside-in signaling and affinity by the beta2 I domain of integrin alphaLbeta2.
The adhesiveness of integrin alpha(L)beta(2) is modulated by divalent cations. We mutated three metal ion-binding sites in the beta(2) I domain. The metal ion-dependent adhesion site (MIDAS) and the ligand-induced metal-binding site are required for ligand binding and sufficient for synergism between Ca(2+) and Mg(2+). Adjacent to MIDAS (ADMIDAS) mutants are constitutively active but remain bent, with poor exposure of a beta(2) stalk region epitope. Fluorescence resonance energy transfer between fluorescent protein-fused alpha(L) and beta(2) cytoplasmic domains showed that ADMIDAS mutation abrogated ligand binding-induced spatial separation of cytoplasmic domains. Furthermore, ADMIDAS mutation abolished spreading on ligand-bearing substrates. Thus, beta(2) I domain metal ion-binding sites regulate alpha(L) I domain affinity, and the ADMIDAS is required for outside-in signaling.
Chen
JianFeng
J
CBR Institute for Biomedical Research and Department of Pathology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA.
Yang
Wei
W
Kim
Minsoo
M
Carman
Christopher V
CV
Springer
Timothy A
TA
D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002413:Cations, Divalent / Q000378:metabolism; D002448:Cell Adhesion; D002465:Cell Movement; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D015536:Down-Regulation / Q000235:genetics; D006801:Humans; D020014:K562 Cells; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1 / Q000737:chemistry* / Q000378:metabolism*; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D015854:Up-Regulation / Q000235:genetics
D002413:Cations, Divalent; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1; D050505:Mutant Proteins; D002118:Calcium