Acta Crystallographica Section D

Biological Crystallography

Volume 69, Part 3 (March 2013)

research papers

Acta Cryst. (2013). D69, 388-397    [ doi:10.1107/S0907444912048664 ]

Structure of a human IgA1 Fab fragment at 1.55 Å resolution: potential effect of the constant domains on antigen-affinity modulation

A. Correa, F. Trajtenberg, G. Obal, O. Pritsch, G. Dighiero, P. Oppezzo and A. Buschiazzo

Abstract: Despite being the most abundant class of immunoglobulins in humans and playing central roles in the adaptive immune response, high-resolution structural data are still lacking for the antigen-binding region of human isotype A antibodies (IgAs). The crystal structures of a human Fab fragment of IgA1 in three different crystal forms are now reported. The three-dimensional organization is similar to those of other Fab classes, but FabA1 seems to be more rigid, being constrained by a hydrophobic core in the interface between the variable and constant domains of the heavy chain (VH-CH1) as well as by a disulfide bridge that connects the light and heavy chains, influencing the relative heavy/light-chain orientation. The crystal structure of the same antibody but with a G-isotype CH1 which is reported to display different antigen affinity has also been solved. The differential structural features reveal plausible mechanisms for constant/variable-domain long-distance effects whereby antibody class switching could alter antigen affinity.

PDB references: 3m8o, 3qnx, 3qny, 3qo1 and 3qnz

Keywords: antibodies; antigen-affinity control; human IgA; protein conformational entropy.

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[ doi:10.1107/S0907444912048664/rr5031sup1.pdf ]
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