Structural basis for the peptidoglycan recognition by Helicobacter pylori Csd4

Helicobacter pylori infection causes a variety of gastrointestinal diseases including peptic ulcers and gastric cancer. The colonization of this bacterium in the gastric mucosa is required for the survival in the stomach. Its colonization of the gastric mucosa of human stomach depends on its motility, which is facilitated by the helical cell shape. In H. pylori, crosslinking relaxation or trimming of peptidoglycan muropeptide affects the helical shape. Among several cell shape-determining peptidoglycan hydrolases identified in H. pylori, Csd4 is a Zn2+-dependent D,L-carboxypeptidase that cleaves the bond between the γ-D-Glu and mDAP bond of the uncrosslinked tripeptide of peptidoglycan (L-Ala-γ-D-Glu-mDAP) to produce L-Ala-γ-D-Glu dipeptide and mDAP, promoting the helical cell shape. Inhibition of D,L-carboxypeptidase activity of Csd4 may represent a novel therapeutic approach. We report here the crystal structures of H. pylori Csd4 in three different states: the ligand-free form, the substrate-bound form, and the product-bound form. H. pylori Csd4 consists of three domains: an N-terminal D,L-carboxypeptidase domain, a novel β-barrel domain, and a C-terminal immunoglobulin-like domain. Our ligand-bound structures provide structural basis of peptidoglycan recognition by D,L-carboxypeptidase. H. pylori Csd4 recognizes primarily the terminal mDAP of the tripeptide substrate and undergoes a significant structural change upon binding either mDAP or mDAP-containing tripeptide.

Insulin as a Primary Autoantigen for Type 1A Diabetes

Type 1A diabetes mellitus is caused by specific and progressive autoimmune destruction of the beta cells in the islets of Langerhans whereas the other cell types in the islet (alpha, delta, and PP) are spared. The autoantigens of Type 1A diabetes may be divided into subgroups based on their tissue distributions: Beta-cell-specific antigens like insulin, insulin derivatives, and IGRP (Islet-specific Glucose-6-phosphatase catalytic subunit Related Peptide); neurendocrine antigens such as carboxypeptidase H, insulinoma-associated antigen (IA-2), glutamic acid decarboxylase (GAD65), and carboxypeptidase E; and those expressed ubiquitously like heat shock protein 60 (a putative autoantigen for type 1 diabetes). This review will focus specifically on insulin as a primary autoantigen, an essentia l target for disease, in type 1A diabetes mellitus. In particular, immunization with insulin peptide B:9-23 can be used to induce insulin autoantibodies and diabetes in animal models or used to prevent diabetes. Genetic manipulation of the insulin 1 and 2 genes reciprocally alters development of diabetes in the NOD mouse, and insulin gene polymorphisms are important determinants of childhood diabetes. We are pursuing the hypothesis that insulin is a primary autoantigen for type 1 diabetes, and thus the pathogenesis of the disease relates to specific recognition of one or more peptides.