2ywy
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(New page: 200px<br /> <applet load="2ywy" size="450" color="white" frame="true" align="right" spinBox="true" caption="2ywy, resolution 2.71Å" /> '''Structure of new an...)
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Revision as of 07:45, 18 November 2007
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Structure of new antigen receptor variable domain from sharks
Overview
Mimotopes mimic the three-dimensional topology of an antigen epitope, and, are frequently recognized by antibodies with affinities comparable to, those obtained for the original antibody-antigen interaction. Peptides and, anti-idiotypic antibodies are two classes of protein mimotopes that mimic, the topology (but not necessarily the sequence) of the parental antigen., In this study, we combine these two classes by selecting mimotopes based, on single domain IgNAR antibodies, which display exceptionally long CDR3, loop regions (analogous to a constrained peptide library) presented in the, context of an immunoglobulin framework with adjacent and supporting CDR1, loops. By screening an in vitro phage-display library of IgNAR variable, domains (V(NAR)s) against the target antigen monoclonal antibody MAb5G8, we obtained four potential mimotopes. MAb5G8 targets a linear tripeptide, epitope (AYP) in the flexible signal sequence of the Plasmodium falciparum, Apical Membrane Antigen-1 (AMA1), and this or similar motifs were detected, in the CDR loops of all four V(NAR)s. The V(NAR)s, 1-A-2, -7, -11, and, -14, were demonstrated to bind specifically to this paratope by, competition studies with an artificial peptide and all showed enhanced, affinities (3-46 nM) compared to the parental antigen (175 nM)., Crystallographic studies of recombinant proteins 1-A-7 and 1-A-11 showed, that the SYP motifs on these V(NAR)s presented at the tip of the exposed, CDR3 loops, ideally positioned within bulge-like structures to make, contact with the MAb5G8 antibody. These loops, in particular in 1-A-11, were further stabilized by inter- and intra- loop disulphide bridges, hydrogen bonds, electrostatic interactions, and aromatic residue packing., We rationalize the higher affinity of the V(NAR)s compared to the parental, antigen by suggesting that adjacent CDR1 and framework residues contribute, to binding affinity, through interactions with other CDR regions on the, antibody, though of course definitive support of this hypothesis will rely, on co-crystallographic studies. Alternatively, the selection of mimotopes, from a large (<4 x 10(8)) constrained library may have allowed selection, of variants with even more favorable epitope topologies than present in, the original antigenic structure, illustrating the power of in vivo, selection of mimotopes from phage-displayed molecular libraries. Proteins, 2007. (c) 2007 Wiley-Liss, Inc.
About this Structure
2YWY is a Protein complex structure of sequences from Orectolobus maculatus. Full crystallographic information is available from OCA.
Reference
Shark IgNAR antibody mimotopes target a murine immunoglobulin through extended CDR3 loop structures., Simmons DP, Streltsov VA, Dolezal O, Hudson PJ, Coley AM, Foley M, Proll DF, Nuttall SD, Proteins. 2007 Oct 11;. PMID:17932913
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