Crystallographic analysis of the NNA7 Fab and proposal for the mode of human blood-group recognition.Xie, K., Song, S.C., Spitalnik, S.L., Wedekind, J.E.
(2005) Acta Crystallogr.,Sect.D 61: 1386-1394
- PubMed: 16204891
- DOI: 10.1107/S0907444905023851
- PubMed Abstract:
- Purification, crystallization and X-ray diffraction analysis of a recombinant Fab that recognizes a human blood-group antigen
Song, S.C.,Xie, K.,Czerwinski, M.,Spitalnik, S.L.,Wedekind, J.E.
(2004) ACTA CRYSTALLOGR.,SECT.D 60: 788
The NNA7 Fab antibody fragment recognizes the human N-type blood-group antigen comprised of the N-terminal glycopeptide of glycophorin A (GPA). A mutant form of this Fab fragment, NNA7-G91S, exhibits markedly reduced antigen binding. To provide insig ...
The NNA7 Fab antibody fragment recognizes the human N-type blood-group antigen comprised of the N-terminal glycopeptide of glycophorin A (GPA). A mutant form of this Fab fragment, NNA7-G91S, exhibits markedly reduced antigen binding. To provide insight into how these Fab fragments recognize this glycopeptide antigen, the crystal structures of NNA7 and NNA7-G91S were solved and refined to 1.83 and 1.97 A resolution, respectively. Both molecules are composed of the same heavy (H) chain Fd fragment, but each contains a slightly different light (L) chain owing to the G91S substitution. Specifically, the G91S mutation pushes the backbone of the neighboring H chain away from complementarity-determining region 3 (CDR3) of the L-chain variable region, allowing an additional glycerol cryoprotectant molecule to enter the antigen-combining site near the putative location of O-linked glycosylation. Each Fab fragment also possesses a well defined 2-(N-morpholino)ethanesulfonic acid (MES) molecule trapped in its antigen-combining site, as well as a crystallographic symmetry-related molecule comprising an amino-acid sequence that is virtually identical to the N-terminus of GPA. The MES molecule interacts with the H-chain CDR in a manner reminiscent of antibody-carbohydrate complexes. These results suggest a model for recognition of the glycopeptide antigen that accounts for the deleterious effect of the G91S substitution.
Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA.