Structure and allosteric regulation of the alpha X beta 2 integrin I domain

• Published in: Proceedings of the National Academy of Sciences - PNAS 2003-02, Vol.100 (4), p.1873-1878
• Main Authors: Vorup-Jensen, Thomas, Ostermeier, Christian, Shimaoka, Motomu, Hommel, Ulrich, Springer, Timothy A
• Format: Article
• Language: English
• Subjects: Allosteric Regulation; Amino Acid Sequence; Base Sequence; Crystallography, X-Ray; DNA Primers; Integrin alphaXbeta2 - chemistry; Integrin alphaXbeta2 - genetics; Integrin alphaXbeta2 - metabolism; Molecular Sequence Data; Protein Denaturation; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Sequence Homology, Amino Acid; Surface Plasmon Resonance
• ISSN: 0027-8424
• DOI: 10.1073/pnas.0237387100

The integrin alpha X beta 2 (CD11c/CD18, p150,95) binds ligands through the I domain of the alpha X subunit. Ligands include the complement factor fragment iC3b, a key component in the innate immune defense, which, together with the expression of alpha X beta 2 on dendritic cells and on other leukocytes, suggests a role in the immune response. We now report the structure of the alpha X I domain resolved at 1.65 A by x-ray crystallography. To analyze structural requirements for ligand binding we made a mutation in the alpha X I domain C-terminal helix, which increased the affinity for iC3b approximately 200-fold to 2.4 microM compared with the wild-type domain affinity of approximately 400 microM. Gel permeation chromatography supported a conformational change between the wild-type and mutated domains. Conservation of allosteric regulation in the alpha X I domain points to the functional importance of this phenomenon.