Apa is a trimeric autotransporter adhesin of Actinobacillus pleuropneumoniae responsible for autoagglutination and host cell adherence

Abstract

Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia, and adherence to host cells is a key step in the pathogenic process. Although trimeric autotransporter adhesins (TAAs) were identified in many pathogenic bacteria in recent years, none in A. pleuropneumoniae have been characterized. In this study, we identified a TAA from A. pleuropneumoniae, Apa, and characterized the contribution of its amino acid residues to the adhesion process. Sequence analysis of the C-terminal amino acid residues of Apa revealed the presence of a putative translocator domain and six conserved HsfBD1-like or HsfBD2-like binding domains. Western blot analysis revealed that the 126 C-terminal amino acids of Apa could form trimeric molecules. By confocal laser scanning microscopy, one of these six domains (ApaBD3) was determined to mediate adherence to epithelial cells. Adherence assays and adherence inhibition assays using a recombinant E. coli- ApaBD3 strain which expressed ApaBD3 on the surface of E. coli confirmed that this domain was responsible for the adhesion activity. Moreover, cellular enzyme-linked immunosorbent assays demonstrated that ApaBD3 mediated high-level adherence to epithelial cell lines. Intriguingly, autoagglutination was observed with the E. coli- ApaBD3 strain, and this phenomenon was dependent upon the association of the expressed ApaBD3 with the C-terminal translocator domain.

Molecular Analysis of an Alternative N-Glycosylation Machinery by Functional Transfer from Actinobacillus pleuropneumoniae to Escherichia coli

“…The E. coli expression system provides an inexpensive way to produce glycosylated adhesins for diagnostics or vaccination purposes. The autotransporter adhesins of A. pleuropneumoniae mediate adhesion to the host cells and are therefore crucial for colonization and pathogenesis (38). All sequenced strains of A. pleuropneumoniae as well as a number of other pathogenic Pasteurellaceae species (such as H. influenzae or M. haemolytica), carry genes encoding a cytoplasmic glycosylation system.…”

Structural Basis for Toughness and Flexibility in the C-terminal Passenger Domain of an Acinetobacter Trimeric Autotransporter Adhesin

“…Recently, many TAAs have been further identified, such as BtaE of Brucella spp. (18), Apa of Actinobacillus pleuropneumoniae (19), and EibD of Escherichia coli (20). Ata of Acinetobacter baumannii is involved in nosocomial infection (21).…”

New findings on the function and potential applications of the trimeric autotransporter adhesin

“…TAAs have attracted significant attention since their discovery on the Y. enterocolitica surface. In addition to YadA, Hia and Hif, recent studies have suggested that several additional life-threatening infectious Gram-negative bacteria possess one or more TAAs; these proteins include Apa from Actinobacillus pleuropneumoniae (Xiao et al 2012), SadA from Salmonella enterica (Raghunathan et al 2011), BpaA from Burkholderia pseudomallei (Edwards et al 2010), BadA from Bartonella (Riess et al 2004;, EmaA from Actinobacillus actinomycetemcomitans (Mintz 2004), and Cha from Haemophilus (Sheets et al 2008).…”