PDBsum entry 1xed

Immune system

PDB id: 1xed

Contents

Protein chains

111 a.a.

105 a.a.

111 a.a.

Metals

_MG ×2

Waters ×158

References listed in PDB file

Key reference

• Title: Crystal structure of a polymeric immunoglobulin binding fragment of the human polymeric immunoglobulin receptor.
• Authors: A.E.Hamburger, A.P.West, P.J.Bjorkman.
• Ref.: Structure, 2004, 12, 1925-1935. [DOI no: 10.1016/j.str.2004.09.006]
• PubMed id: 15530357

Abstract

The polymeric immunoglobulin receptor (pIgR) is a type I transmembrane protein that delivers dimeric IgA (dIgA) and pentameric IgM to mucosal secretions. Here, we report the 1.9 A resolution X-ray crystal structure of the N-terminal domain of human pIgR, which binds dIgA in the absence of other pIgR domains with an equilibrium dissociation constant of 300 nM. The structure of pIgR domain 1 reveals a folding topology similar to immunoglobulin variable domains, but with differences in the counterparts of the complementarity determining regions (CDRs), including a helical turn in CDR1 and a CDR3 loop that points away from the other CDRs. The unusual CDR3 loop position prevents dimerization analogous to the pairing of antibody variable heavy and variable light domains. The pIgR domain 1 structure allows interpretation of previous mutagenesis results and structure-based comparisons between pIgR and other IgA receptors.

Figure 5.
Figure 5. Mutagenesis Data Mapped onto StructureThe positions of substitutions that abolished (red) or decreased (blue) pIgA binding to rabbit pIgR (Coyne et al., 1994) are mapped onto the human pIgR D1 structure. A close-up of the CDR1 region is shown in the upper right, and the sequence of CDR1 in human and rabbit pIgR D1 is shown in the lower right. Val29 (black), which is solvent exposed in the D1 structure, was assumed to be buried and was therefore not substituted (Bakos et al. 1993 and Coyne et al. 1994).

The above figure is reprinted by permission from Cell Press: Structure (2004, 12, 1925-1935) copyright 2004.