A Common NH53K Mutation in the Combining Site of Antibodies Raised against Chlamydial LPS Glycoconjugates Significantly Increases Avidity

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• 作者：Ryan J. Blackler ; Sven Mu虉ller-Loennies ; Cory L. Brooks ; Dylan W. Evans ; Lore Brade ; Paul Kosma ; Helmut Brade ; Stephen V. Evans
• 刊名：Biochemistry
• 出版年：2011
• 出版时间：April 26, 2011
• 年：2011
• 卷：50
• 期：16
• 页码：3357-3368
• 全文大小：1382K
• 年卷期：v.50,no.16(April 26, 2011)
• ISSN：1520-4995

文摘

The crystal structures of the antigen-binding fragment of the murine monoclonal antibody (mAb) S25-39 in the presence of several antigens representing chlamydial lipopolysaccharide (LPS) epitopes based on the bacterial sugar 3-deoxy-伪-d-manno-oct-2-ulosonic acid (Kdo) have been determined at resolutions from 2.4 to 1.8 脜. The antigen-binding site of this antibody differs from the well-characterized antibody S25-2 by a single mutation away from the germline of asparagine H53 to lysine, yet this one mutation results in a significant increase in avidity across a range of antigens. A comparison of the two antibody structures reveals that the mutated Lys H53 forms additional hydrogen bonds and/or charged-residue interactions with the second Kdo residue of every antigen having two or more carbohydrate residues. Significantly, the NH53K mutation results from a single nucleotide substitution in the germline sequence common among a panel of antibodies raised against glycoconjugates containing carbohydrate epitopes of chlamydial LPS. Like S25-2, S25-39 displays significant induced fit of complementarity determining region (CDR) H3 upon antigen binding, with the unliganded structure possessing a conformation distinct from those reported earlier for S25-2. The four different observed conformations for CDR H3 suggest that this CDR has evolved to exploit the recognition potential of a flexible loop while minimizing the associated entropic penalties of binding by adopting a limited number of ordered conformations in the unliganded state. These observations reveal strategies evolved to balance adaptability and specificity in the germline antibody response to carbohydrate antigens.