A serine protease zymogen functions as a pattern-recognition receptor for lipopolysaccharides

Shigeru Ariki, Kumiko Koori, Tsukasa Osaki, Kiyohito Motoyama, Kei Ichiro Inamori, Shun Ichiro Kawabata

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78 Citations (Scopus)


Bacterial lipopolysaccharide (LPS)-induced exocytosis of granular hemocytes is a key component of the horseshoe crab's innate immunity to infectious microorganisms; stimulation by LPS induces the secretion of various defense molecules from the granular hemocytes. Using a previously uncharacterized assay for exocytosis, we clearly show that hemocytes respond only to LPS and not to other pathogen-associated molecular patterns, such as β-1,3-glucans and peptidoglycans. Furthermore, we show that a granular protein called factor C, an LPS-recognizing serine protease zymogen that initiates the hemolymph coagulation cascade, also exists on the hemocyte surface as a biosensor for LPS. Our data demonstrate that the proteolytic activity of factor C is both necessary and sufficient to trigger exocytosis through a heterotrimeric GTP-binding protein-mediating signaling pathway. Exocytosis of hemocytes was not induced by thrombin, but it was induced by hexapeptides corresponding to the tethered ligands of protease-activated G protein-coupled receptors (PARs). This finding suggested the presence of a PAR-like receptor on the hemocyte surface. We conclude that the serine protease zymogen on the hemocyte surface functions as a pattern-recognition protein for LPS.

Original languageEnglish
Pages (from-to)953-958
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number4
Publication statusPublished - Jan 27 2004

All Science Journal Classification (ASJC) codes

  • General


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