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Ecotin, a microbial inhibitor of serine proteases, blocks multiple complement dependent and independent microbicidal activities of human serum.

Abstract：

:Ecotin is a serine protease inhibitor produced by hundreds of microbial species, including pathogens. Here we show, that ecotin orthologs from Escherichia coli, Yersinia pestis, Pseudomonas aeruginosa and Leishmania major are potent inhibitors of MASP-1 and MASP-2, the two key activator proteases of the complement lectin pathway. Factor D is the key activator protease of another complement activation route, the alternative pathway. We show that ecotin inhibits MASP-3, which is the sole factor D activator in resting human blood. In pathway-specific ELISA tests, we found that all ecotin orthologs are potent lectin pathway inhibitors, and at high concentration, they block the alternative pathway as well. In flow cytometry experiments, we compared the extent of complement-mediated opsonization and lysis of wild-type and ecotin-knockout variants of two E. coli strains carrying different surface lipopolysaccharides. We show, that endogenous ecotin provides significant protections against these microbicidal activities for both bacteria. By using pathway specific complement inhibitors, we detected classical-, lectin- and alternative pathway-driven complement attack from normal serum, with the relative contributions of the activation routes depending on the lipopolysaccharide type. Moreover, in cell proliferation experiments we observed an additional, complement-unrelated antimicrobial activity exerted by heat-inactivated serum. While ecotin-knockout cells are highly vulnerable to these activities, endogenous ecotin of wild-type bacteria provides complete protection against the lectin pathway-related and the complement-unrelated attack, and partial protection against the alternative pathway-related damage. In all, ecotin emerges as a potent, versatile self-defense tool that blocks multiple antimicrobial activities of the serum. These findings suggest that ecotin might be a relevant antimicrobial drug target.

journal_name

PLoS Pathog

journal_title

PLoS pathogens

authors

Nagy ZA,Szakács D,Boros E,Héja D,Vígh E,Sándor N,Józsi M,Oroszlán G,Dobó J,Gál P,Pál G

doi

10.1371/journal.ppat.1008232

subject

Has Abstract

pub_date

2019-12-20 00:00:00

pages

e1008232

issue

eissn

1553-7366

issn

1553-7374

pii

PPATHOGENS-D-19-01280

journal_volume

pub_type

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Ecotin, a microbial inhibitor of serine proteases, blocks multiple complement dependent and independent microbicidal activities of human serum.