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|2oz4, resolution 2.70Å ()|
|Ligands:||, , , ,|
|Gene:||ICAM1 (Homo sapiens)|
Structural Plasticity in IgSF Domain 4 of ICAM-1 Mediates Cell Surface Dimerization
The Ig superfamily (IgSF) intercellular adhesion molecule-1 (ICAM-1) equilibrates between monomeric and dimeric forms on the cell surface, and dimerization enhances cell adhesion. A crystal structure of ICAM-1 IgSF domains (D) 3-5 revealed a unique dimerization interface in which D4s of two protomers fuse through edge beta-strands to form a single super beta-sandwich domain. Here, we describe a crystal structure at 2.7-A resolution of monomeric ICAM-1 D3-D5, stabilized by the monomer-specific Fab CA7. CA7 binds to D5 in a region that is buried in the dimeric interface and is distal from the dimerization site in D4. In monomeric ICAM-1 D3-D5, a 16-residue loop in D4 that is disordered in the dimeric structure could clearly be traced as a BC loop, a short C strand, and a CE meander with a cis-Pro followed by a solvent-exposed, flexible four-residue region. Deletions of 6 or 10 residues showed that the C-strand is essential for monomer stability, whereas a distinct six-residue deletion showed little contribution of the CE meander. Mutation of two inward-pointing Leu residues in edge beta-strand E to Lys increased monomer stability, confirming the hypothesis that inward-pointing charged side chains on edge beta-strands are an important design feature to prevent beta-supersheet formation. Overall, the studies reveal that monomer-dimer transition is associated with a surprisingly large, physiologically relevant, IgSF domain rearrangement.
Structural plasticity in Ig superfamily domain 4 of ICAM-1 mediates cell surface dimerization., Chen X, Kim TD, Carman CV, Mi LZ, Song G, Springer TA, Proc Natl Acad Sci U S A. 2007 Sep 25;104(39):15358-63. Epub 2007 Sep 19. PMID:17881562
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
About this Structure
- Chen X, Kim TD, Carman CV, Mi LZ, Song G, Springer TA. Structural plasticity in Ig superfamily domain 4 of ICAM-1 mediates cell surface dimerization. Proc Natl Acad Sci U S A. 2007 Sep 25;104(39):15358-63. Epub 2007 Sep 19. PMID:17881562