Integrin activation involves a conformational change in the alpha 1 helix of the beta subunit A-domain.
The ligand-binding region of integrin beta subunits contains a von Willebrand factor type A-domain: an alpha/beta "Rossmann" fold containing a metal ion-dependent adhesion site (MIDAS) on its top face. Although there is evidence to suggest that the betaA-domain undergoes changes in tertiary structure during receptor activation, the identity of the secondary structure elements that change position is unknown. The mAb 12G10 recognizes a unique cation-regulated epitope on the beta(1) A-domain, induction of which parallels the activation state of the integrin (i.e. competency for ligand recognition). The ability of Mn(2+) and Mg(2+) to stimulate 12G10 binding is abrogated by mutation of the MIDAS motif, demonstrating that the MIDAS is a Mn(2+)/Mg(2+) binding site and that occupancy of this site induces conformational changes in the A-domain. The cation-regulated region of the 12G10 epitope maps to Arg(154)/Arg(155) in the alpha1 helix. Our results demonstrate that the alpha1 helix undergoes conformational alterations during integrin activation and suggest that Mn(2+) acts as a potent activator of beta(1) integrins because it can promote a shift in the position of this helix. The mechanism of beta subunit A-domain activation appears to be distinct from that of the A-domains found in some integrin alpha subunits.
Mould
A Paul
AP
Wellcome Trust Centre for Cell-Matrix Research, School of Biological Sciences, University of Manchester, Manchester M13 9PT, United Kingdom. paul.mould@man.ac.uk
Askari
Janet A
JA
Barton
Stephanie
S
Kline
Adam D
AD
McEwan
Paul A
PA
Craig
Susan E
SE
Humphries
Martin J
MJ
D000818:Animals; D015703:Antigens, CD / Q000737:chemistry; D001120:Arginine / Q000737:chemistry; D001665:Binding Sites; D002412:Cations; D004305:Dose-Response Relationship, Drug; D004797:Enzyme-Linked Immunosorbent Assay; D018604:Epitope Mapping; D000939:Epitopes / Q000737:chemistry; D005353:Fibronectins / Q000737:chemistry; D006801:Humans; D039482:Integrin alpha5; D019012:Integrin beta1 / Q000737:chemistry; D016023:Integrins / Q000737:chemistry* / Q000378:metabolism*; D008024:Ligands; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D008958:Models, Molecular; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats
D015703:Antigens, CD; D002412:Cations; D000939:Epitopes; D005353:Fibronectins; D039482:Integrin alpha5; D019012:Integrin beta1; D016023:Integrins; D008024:Ligands; D008345:Manganese; D001120:Arginine; D008274:Magnesium