title: 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.
authors.affiliation: College of Animal Science and Veterinary Medicine, JiLin University, Changchun, PR China.
authors.forename: Longwen
authors.initials: L
authors.lastname: Xiao
authors.forename: Liang
authors.initials: L
authors.lastname: Zhou
authors.forename: Changjiang
authors.initials: C
authors.lastname: Sun
authors.forename: Xin
authors.initials: X
authors.lastname: Feng
authors.forename: ChongTao
authors.initials: C
authors.lastname: Du
authors.forename: Yu
authors.initials: Y
authors.lastname: Gao
authors.forename: Qun
authors.initials: Q
authors.lastname: Ji
authors.forename: Shuxin
authors.initials: S
authors.lastname: Yang
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.forename: Wenyu
authors.initials: W
authors.lastname: Han
authors.forename: P R
authors.initials: PR
authors.lastname: Langford
authors.forename: Liancheng
authors.initials: L
authors.lastname: Lei
mesh_terms: D016977:Actinobacillus pleuropneumoniae / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018829:Adhesins, Bacterial / Q000235:genetics / Q000378:metabolism*; D020816:Amino Acid Motifs; D000818:Animals; D001422:Bacterial Adhesion; D002460:Cell Line; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004847:Epithelial Cells / Q000382:microbiology; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D018613:Microscopy, Confocal; D017434:Protein Structure, Tertiary; D017422:Sequence Analysis, DNA; D013552:Swine; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D018829:Adhesins, Bacterial; D004269:DNA, Bacterial; D026901:Membrane Transport Proteins; D037521:Virulence Factors