TleA, a Tsh-Like Autotransporter Identified in a Human Enterotoxigenic Escherichia coli Strain

Abstract

e Enterotoxigenic Escherichia coli (ETEC), a leading cause of acute diarrhea, colonizes the intestine by means of adhesins. However, 15 to 50% of clinical isolates are negative for known adhesins, making it difficult to identify antigens for broad-coverage vaccines. The ETEC strain 1766a, obtained from a child with watery diarrhea in Chile, harbors the colonization factor CS23 but is negative for other known adhesins. One clone, derived from an ETEC 1766a genomic library (clone G10), did not produce CS23 yet was capable of adhering to Caco-2 cells. The goal of this study was to identify the gene responsible for this capacity. Random transposon-based mutagenesis allowed the identification of a 4,110-bp gene that codes for a homologue of the temperature-sensitive hemagglutinin (Tsh) autotransporter described in avian E. coli strains (97% identity, 90% coverage) and that is called TleA (Tsh-like ETEC autotransporter) herein. An isogenic ETEC 1766a strain with a tleA mutation showed an adhesion level similar to that of the wild-type strain, suggesting that the gene does not direct attachment to Caco-2 cells. However, expression of tleA conferred the capacity for adherence to nonadherent E. coli HB101. This effect coincided with the detection of TleA on the surface of nonpermeabilized bacteria, while, conversely, ETEC 1766a seems to secrete most of the produced autotransporter to the medium. On the other hand, TleA was capable of degrading bovine submaxillary mucin and leukocyte surface glycoproteins CD45 and P-selectin glycoprotein ligand 1 (PSGL-1). These results suggest that TleA promotes colonization of the intestinal epithelium and that it may modulate the host immune response.

Three new serine-protease autotransporters of Enterobacteriaceae (SPATEs) from extra-intestinal pathogenic Escherichia coli and combined role of SPATEs for cytotoxicity and colonization of the mouse kidney

“…is the class 2 SPATE EaaA, identified from commensal E. coli ECOR-9 [59] (Figure 2). Sha shares more identity to class 2 SPATEs Tsh/Hbp (66% identity) [36,63], TleA (60% identity) [64] and Vat (56% identity) [45]. As such, Sha is likely to share other properties more similar to Tsh (adhesin, hemagglutinin) and Vat (cytotoxin), and the elastase-like substrate specificity of Sha, also shown for Tsh and Vat, is in line with this.…”

Serine Protease Autotransporters of the Enterobacteriaceae (SPATEs): Out and About and Chopping It Up

“…TleA may have a role in intestinal colonization and immunomodulation as it was shown to degrade bovine submaxillary mucin and leukocyte surface glycoproteins CD45 and P-selectin glycoprotein ligand 1. Further, nonadherent E. coli HB101 expressing TleA conferred the capacity to adhere to Caco-2 cells, while such adherence was not observed in the wild-type ETEC strain 1766a [68].…”

“…Tsh-like ETEC autotransporter or TleA (GenBank Accession No. KF494347) is an AT that was identified in an ETEC strain [68]. It is a 4110-bp gene that encodes a 1369-amino-acid precursor.…”

“…Sequence analyses have shown that TleA contains a signal peptide from residues 1 to 52, a passenger domain from residues 53 to 1092 with a serine protease motif GDSGS from residues 257 to 261 and a β-barrel domain from residues 1093 to 1369. The alignment of the passenger domain sequences of the other members of SPATEs indicated that TleA is a class 2 SPATE and shares 97% identity with the Tsh autotransporter [68]. TleA may have a role in intestinal colonization and immunomodulation as it was shown to degrade bovine submaxillary mucin and leukocyte surface glycoproteins CD45 and P-selectin glycoprotein ligand 1.…”

Animal EnterotoxigenicEscherichia coli

“…Iha is another adhesin usually associated with shigatoxin-producing E. coli that can be detected in some animal ETEC (495, 498). In addition to AIDA and Iha, it is likely that animal ETEC express other virulence factors, including some non-fimbrial adhesins and proteases described for certain human ETEC strains, such as the adhesins and invasins Tia and autotransporter protein TibA (499–502), the autotransporter adhesin TleA (503), the host-activated adhesin EaeH (504, 505), the two partner secreted EtpA adhesin that binds to the flagellar tip and acts as an adhesive bridge (506), the mucin-degrading proteases EatA, an autotransporter serine protease, and YghJ, a secreted metalloprotease (507, 508). Genomic studies and molecular epidemiology will help to evaluate the presence, distribution and frequencies of these or similar virulence factors in animal ETEC strains (509–511), whereas expression and functional investigations will be needed to identify new animal specific factors and potential host-adapted activation dependency (504).…”