Genome-Wide Analysis of Antigen 43 (Ag43) Variants: New Insights in Their Diversity, Distribution and Prevalence in Bacteria

Abstract

Antigen 43 (Ag43) expression induces aggregation and biofilm formation that has consequences for bacterial colonisation and infection. Ag43 is secreted through the Type 5 subtype “a” secretion system (T5aSS) and is a prototypical member of the family of self-associating autotransporters (SAATs). As a T5aSS protein, Ag43 has a modular architecture comprised of (i) a signal peptide, (ii) a passenger domain that can be subdivided into three subdomains (SL, EJ, and BL), (iii) an autochaperone (AC) domain, and (iv) an outer membrane translocator. The cell-surface SL subdomain is directly involved in the “Velcro-handshake” mechanism resulting in bacterial autoaggregation. Ag43 is considered to have a ubiquitous distribution in E. coli genomes and many strains harbour multiple agn43 genes. However, recent phylogenetic analyses indicated the existence of four distinct Ag43 classes exhibiting different propensities for autoaggregation and interactions. Given the knowledge of the diversity and distribution of Ag43 in E. coli genomes is incomplete, we have performed a thorough in silico investigation across bacterial genomes. Our comprehensive analyses indicate that Ag43 passenger domains cluster in six phylogenetic classes associated with different SL subdomains. The diversity of Ag43 passenger domains is a result of the association of the SL subtypes with two different EJ-BL-AC modules. We reveal that agn43 is almost exclusively present among bacterial species of the Enterobacteriaceae family and essentially in the Escherichia genus (99.6%) but that it is not ubiquitous in E. coli. The gene is typically present as a single copy but up to five copies of agn43 with different combinations of classes can be observed. The presence of agn43 as well as its different classes appeared to differ between Escherichia phylogroups. Strikingly, agn43 is present in 90% of E. coli from E phylogroup. Our results shed light on Ag43 diversity and provide a rational framework for investigating its role in E. coli ecophysiology and physiopathology.

Unveiling the impact of cryptic plasmids curing on Escherichia coli Nissle 1917: massive increase in Ag43c expression

“…The EcN genome harbors three copies of the Ag43 gene (named fluA , fluB , fluC ), expressing three Ag43 variants (named Ag43a, Ag43b, Ag43c), with the lengths of 1040 aa, 1039 aa, and 948 aa, respectively. Recent research has classified Ag43 variants into six distinct categories according to phylogenetic analyses, denoted as C1, C2, C3, C4, C5, and C6 (Ageorges et al 2023 ). In EcN, Ag43a and Ag43b fall into the C3 category, while Ag43c belongs to the C6 category.…”

“…Ag43c, like other variants of Ag43, possesses a modular structure (Fig. 4 a), including: the N-terminal signal sequence (SP), the L-type passenger domain (α domain), the autochaperone domain (AC), the C-terminal translocator (β domain) (Ageorges et al 2023 ; Benz and Schmidt 2011 ; Koh et al 2022 ). Upon crossing the inner membrane, the SP sequence is cleaved (Ageorges et al 2019 ; Koh et al 2022 ).…”

“…Upon crossing the inner membrane, the SP sequence is cleaved (Ageorges et al 2019 ; Koh et al 2022 ). After traversing the outer membrane, the region between the AC and β domain is cleaved by an unknown protease (Ageorges et al 2023 ). The Ag43α domain attaches to the cell surface through non-covalent interactions and can be easily released through simple heat treatment (Henderson et al 2004 ; Klemm et al 2003 ; Owen et al 1996 ).…”

A flow cytometry method for quantitative measurement and molecular investigation of the adhesion of bacteria to yeast cells

“…As yeast cell wall are enriched with proteins highly decorated with mannosyl sugars that represents about 40% of the cell wall mass 12,13 , these components can act as antagonist to mannosyl-sugars of the host glycoproteins 14,15 . However, bacteria adhesion to intestinal cells can also occur by other means, such as by afimbrial autotransporter (AT) adhesins that are present among Enterobacteriaceae family of the Escherichia genus 16 , or Tia produced by some enterotoxigenic E. coli (ETEC) 17 .…”