Open AccessSpecies-Specific Functioning of the Pseudomonas XcpQ Secretin: Role for the C-Terminal Homology Domain and Lipopolysaccharide
Author(s) -
Wilbert Bitter,
Ria van Boxtel,
Mathijs Groeneweg,
Patricia Sanchéz-Carballo,
Ulrich Zähringer,
Jan Tommassen,
Margot Koster
Publication year - 2007
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.01583-06
Subject(s) - biology , mutant , alcaligenes , pseudomonas aeruginosa , bacterial outer membrane , homology (biology) , periplasmic space , biochemistry , tyrosine , microbiology and biotechnology , lipopolysaccharide , pseudomonas , amino acid , gene , bacteria , escherichia coli , genetics , endocrinology
Secretins are oligomeric proteins that mediate the export of macromolecules across the bacterial outer membrane. The members of the secretin superfamily possess a C-terminal homology domain that is important for oligomerization and channel formation, while their N-terminal halves are thought to be involved in system-specific interactions. The XcpQ secretin ofPseudomonas spp. is a component of the type II secretion pathway. XcpQ fromPseudomonas alcaligenes is not able to functionally replace the secretin of the closely related speciesPseudomonas aeruginosa. By analysis of chimeric XcpQ proteins, a region important for species-specific functioning was mapped between amino acid residues 344 and 478 in the C-terminal homology domain. Two chromosomal suppressor mutations were obtained that resulted in the proper functioning inP. aeruginosa ofP. alcaligenes XcpQ and inactive hybrids. These mutations caused a defect in the synthesis of the lipopolysaccharide (LPS) outer core region. Subsequent analysis of different LPS mutants showed that changes in the outer core and not the loss of O antigen caused the suppressor phenotype. High concentrations of divalent cations in the growth medium also allowedP. alcaligenes XcpQ and inactive hybrids to function properly inP. aeruginosa . Since divalent cations are known to affect the structure of LPS, this observation supports the hypothesis that LPS has a role in the functioning of secretins.