Broad spectrum activity of a lectin-like bacterial serine protease family on human leukocytes.

Jorge Luis Ayala-Lujan,Araceli E Santiago,Mei Gong,Fernando Ruiz-Perez,Rachel Smith,Vidhya Vijayakumar,Mickaël Desvaux

doi:10.1371/journal.pone.0107920

Jorge Luis Ayala-Lujan, Araceli E Santiago + Show 5 more

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https://doi.org/10.1371/journal.pone.0107920

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Abstract

The serine protease autotransporter from Enterobacteriaceae (SPATE) family, which number more than 25 proteases with apparent diverse functions, have been phylogenetically divided into two distinct classes, designated 1 and 2. We recently demonstrated that Pic and Tsh, two members of the class-2 SPATE family produced by intestinal and extraintestinal pathogenic E. coli, were able to cleave a number of O-glycosylated proteins on neutrophils and lymphocytes resulting in impaired leukocyte functions. Here we show that most members of the class-2 SPATE family have lectin-like properties and exhibit differential protease activity reliant on glycoprotein type and cell lineage. Protease activity was seen in virtually all tested O-glycosylated proteins including CD34, CD55, CD164, TIM1, TIM3, TIM4 and C1-INH. We also show that although SPATE proteins bound and cleaved glycoproteins more efficiently on granulocytes and monocytes, they also targeted glycoproteins on B, T and natural killer lymphocytes. Finally, we found that the characteristic domain-2 of class-2 SPATEs is not required for glycoprotease activity, but single amino acid mutations in Pic domain-1 to those residues naturally occurring in domain-1 of SepA, were sufficient to hamper Pic glycoprotease activity. This study shows that most class-2 SPATEs have redundant activities and suggest that they may function as immunomodulators at several levels of the immune system.

Highlights

The most abundant and functionally diverse proteolytic enzymes in living organisms are the serine proteases [1]
serine protease autotransporters from Enterobacteriaceae (SPATE) are produced by all recognized pathogenic E. coli strains including enteropathogenic E. coli (EPEC), shiga toxinproducing E. coli (STEC), enterotoxigenic E. coli (ETEC), enterohemorrhagic E. coli (EHEC), enteroinvasive E. coli (EIEC), enteroaggregative E. coli (EAEC), diffusely adherent E. coli (DAEC), adherent-invasive E. coli (AIEC), uropathogenic E. coli (UPEC) and by the animal pathogens: avian pathogenic E. coli (APEC) and rabbit pathogenic E. coli (REPEC), all agents of enteric/diarrheal disease [2,3]
We recently showed that Pic and Tsh/Hb cleave a variety of leukocyte surface glycoproteins with diverse roles in numerous cellular and immune functions, and which were substituted with carbohydrates structurally similar to those found on human mucin glycoproteins [11]

Summary

Introduction

The most abundant and functionally diverse proteolytic enzymes in living organisms are the serine proteases [1]. SPATE proteins are produced by enteric pathogens including E. coli, Shigella and recently, found in Salmonella, Edwardsiella, and Citrobacter species [2,3]. SPATEs are secreted members of the autotransporter family, whose secretion involves the excision of the N-terminal region, known as the ‘‘passenger domain’’, from the C-terminal region or ‘‘b-domain domain’’, and subsequent release of the passenger domain (which harbors the proteolytic activity) into the cell surroundings [2,4]. Most knowledge on class 2 SPATEs comes from two members of this family: Tsh/Hbp and the Pic protease. Hbp (Haemoglobin binding protein) identified in the E. coli strain (EB1) [7], isolated from a human wound infection, was shown to differ from Tsh in only two residues. Pic (Protease involved in intestinal colonization) originally identified in Shigella flexneri 2a and EAEC [8], was found to cleave mucin from numerous sources, to induce mucus release [9], Primer Name

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