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Salt-bridge modulates differential calcium-mediated ligand binding to integrin α1- and α2-I domains

Integrins are transmembrane cell-extracellular matrix adhesion receptors that impact many cellular functions. A subgroup of integrins contain an inserted (I) domain within the α–subunits (αI) that mediate ligand recognition where function is contingent on binding a divalent cation at the metal ion d...

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Detalles Bibliográficos
Autores principales: Brown, Kyle L., Banerjee, Surajit, Feigley, Andrew, Abe, Hanna, Blackwell, Timothy S., Pozzi, Ambra, Hudson, Billy G., Zent, Roy
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Nature Publishing Group UK 2018
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5811549/
https://www.ncbi.nlm.nih.gov/pubmed/29440721
http://dx.doi.org/10.1038/s41598-018-21231-1
Descripción
Sumario:Integrins are transmembrane cell-extracellular matrix adhesion receptors that impact many cellular functions. A subgroup of integrins contain an inserted (I) domain within the α–subunits (αI) that mediate ligand recognition where function is contingent on binding a divalent cation at the metal ion dependent adhesion site (MIDAS). Ca(2+) is reported to promote α1I but inhibit α2I ligand binding. We co-crystallized individual I-domains with MIDAS-bound Ca(2+) and report structures at 1.4 and 2.15 Å resolution, respectively. Both structures are in the “closed” ligand binding conformation where Ca(2+) induces minimal global structural changes. Comparisons with Mg(2+)-bound structures reveal Mg(2+) and Ca(2+) bind α1I in a manner sufficient to promote ligand binding. In contrast, Ca(2+) is displaced in the α2I domain MIDAS by 1.4 Å relative to Mg(2+) and unable to directly coordinate all MIDAS residues. We identified an E152-R192 salt bridge hypothesized to limit the flexibility of the α2I MIDAS, thus, reducing Ca(2+) binding. A α2I E152A construct resulted in a 10,000-fold increase in Mg(2+) and Ca(2+) binding affinity while increasing binding to collagen ligands 20%. These data indicate the E152-R192 salt bridge is a key distinction in the molecular mechanism of differential ion binding of these two I domains.