4ma1
Unliganded 3 crystal structure of S25-26 Fab
Structural highlights
Publication Abstract from PubMedThe structure of the antigen-binding fragment of mAb S25-26 determined to 1.95 A resolution in complex with the Chlamydiaceae family-specific trisaccharide antigen Kdo(2-->8)-Kdo(2-->4)Kdo (Kdo=3-deoxy-alpha-D-manno-oct-2-ulopyranosonic acid) displays a germline-coded paratope that differs significantly from previously characterized Chlamydiaceae-specific mAbs, despite being raised against the identical immunogen. Unlike the terminal Kdo recognition pocket that promotes cross-reactivity in S25-2-type antibodies, S25-26 and the closely related S25-23 utilize a groove composed of germline residues to recognize the entire trisaccharide antigen and so confer strict specificity. Interest in S25-23 was sparked by its rare high muM affinity and strict specificity for the family-specific trisaccharide antigen; however, only the related antibody S25-26 proved amenable to crystallization. The structures of three unliganded forms of S25-26 have a labile complementary determining region H3 adjacent to significant glycosylation of the variable heavy chain on asparagine 85 in Framework Region 3. Analysis of the glycan reveals a heterogeneous mixture with a common root structure that contains an unusually high number of terminal alphaGal-Gal moieties. One of the few reported structures of glycosylated mAbs containing these epitopes is the therapeutic antibody Cetuximab; however, unlike Cetuximab, one of the unliganded structures in S25-26 shows significant order in the glycan with appropriate electron density for nine residues. The elucidation of the three dimensional structure of an alphaGal containing N-linked glycan on a mAb variable heavy chain has potential clinical interest, as they have been implicated in allergic response in patients receiving therapeutic antibodies. Groove-type recognition of Chlamydiaceae-specific lipopolysaccharide antigen by a family of antibodies possessing an unusual variable heavy chain N-linked glycan.,Haji-Ghassemi O, Muller-Loennies S, Saldova R, Muniyappa M, Brade L, Rudd PM, Harvey DJ, Kosma P, Brade H, Evans SV J Biol Chem. 2014 Mar 28. PMID:24682362[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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