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Genetic evidence indicates that Drosophila defense against Gram-positive bacteria is mediated by two putative pattern recognition receptors acting upstream of Toll, namely Gram-negative binding protein 1 (GNBP1) and peptidoglycan recognition protein SA (PGRP-SA). Until now however, the molecular recognition proceedings for sensing of Gram-positive pathogens were not known. In the present, we report the physical interaction between GNBP1 and PGRP-SA using recombinant proteins. GNBP1 was able to hydrolyze Gram-positive peptidoglycan (PG), while PGRP-SA bound highly purified PG fragments (muropeptides). Interaction between these proteins was enhanced in the presence of PG or muropeptides. PGRP-SA binding depended on the polymerization status of the muropeptides, pointing to constraints in the number of PGRP-SA molecules bound for signaling initiation. We propose a model whereby GNBP1 presents a processed form of PG for sensing by PGRP-SA and that a tripartite interaction between these proteins and PG is essential for downstream signaling.

Original publication

DOI

10.1038/sj.emboj.7601363

Type

Journal article

Journal

The EMBO journal

Publication Date

05/10/2006

Volume

25

Pages

5005 - 5014

Addresses

Genetics Unit, Department of Biochemistry, University of Oxford, Oxford, UK.

Keywords

Animals, Drosophila melanogaster, Gram-Positive Bacteria, Gram-Positive Bacterial Infections, Peptidoglycan, Carrier Proteins, Drosophila Proteins, Signal Transduction, Antigen Presentation