期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 104, 期 39, 页码 15358-15363出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0707406104
关键词
crystal structure; leukocytes; flow cytometry; mutagenesis
资金
- NCI NIH HHS [R37 CA031798, CA31798, R01 CA031798] Funding Source: Medline
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 P-strands to form a single super beta-sandwich domain. Here, we describe a crystal structure at 2.7-angstrom 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 P-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.
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