This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Mohan, S. Articles by Smith-Gill, S. J. Search for Related Content PubMed PubMed Citation Articles by Mohan, S. Articles by Smith-Gill, S. J.

Modeling the Binding Sites of Anti-Hen Egg White Lysozyme Antibodies HyHEL-8 and HyHEL-26: An Insight into the Molecular Basis of Antibody Cross-Reactivity and Specificity

Structural Biophysics Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, Maryland

Correspondence: Address reprint requests to Dr. Sandra Smith-Gill, PO Box B, Bldg. 469, Rm. 206, CCR, NCI, Frederick, MD 21702. Tel.: 301-846-5203; Fax: 301-846-6326; E-mail: smithgil{at}helix.nih.gov.

Three antibodies, HyHEL-8 (HH8), HyHEL-10 (HH10), and HyHEL-26 (HH26) are specific for the same epitope on hen egg white lysozyme (HEL), and share >90% sequence homology. Their affinities vary by several orders of magnitude, and among the three antibodies, HH8 is the most cross-reactive with kinetics of binding that are relatively invariable compared to HH26, which is highly specific and has quite variable kinetics. To investigate structural correlates of these functional variations, the Fv regions of HH8 and HH26 were homology-modeled using the x-ray structure of the well-characterized HH10-HEL complex as template. The binding site of HH26 is most charged, least hydrophobic, and has the greatest number of intramolecular salt bridges, whereas that of HH8 is the least charged, most hydrophobic and has the fewest intramolecular salt bridges. The modeled HH26-HEL structure predicts the recently determined x-ray structure of HH26, (Li et al., 2003, Nat. Struct. Biol. 10:482–488) with a root-mean-square deviation of 1.03 Å. It is likely that the binding site of HH26 is rendered rigid by a network of intramolecular salt bridges whereas that of HH8 is flexible due to their absence. HH26 also has the most intermolecular contacts with the antigen whereas HH8 has the least. HH10 has these properties intermediate to HH8 and HH26. The structurally rigid binding site with numerous specific contacts bestows specificity on HH26 whereas the flexible binding site with correspondingly fewer contacts enables HH8 to be cross-reactive. Results suggest that affinity maturation may select for high affinity antibodies with either "lock-and-key" preconfigured binding sites, or "preconfigured flexibility" by modulating combining site flexibility.