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Interactions between peptidoglycan and the ExeAB complex during assembly of the type II secretin of Aeromonas hydrophila
Author(s) -
Howard S. Peter,
Gebhart Carol,
Langen Geoffrey R.,
Li Gang,
Strozen Timothy G.
Publication year - 2006
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2005.05003.x
Subject(s) - periplasmic space , biology , peptidoglycan , mutant , aeromonas hydrophila , secretion , amino acid , biochemistry , bacterial outer membrane , inner membrane , secretory protein , microbiology and biotechnology , bacteria , escherichia coli , membrane , genetics , gene
Summary Aeromonas hydrophila transports extracellular protein toxins via the type II secretion system, an export mechanism comprised of numerous proteins that spans both the inner and outer membranes. Two components of this secretion system, ExeA and ExeB, form a complex in the inner membrane that functions to locate and/or assemble the ExeD secretin in the outer membrane. In the studies reported here, two‐codon insertion mutagenesis of exeA revealed that an insertion at amino acid 495 in the C‐terminal region of ExeA did not alter ExeAB complex formation yet completely abrogated its involvement in ExeD secretin assembly and thus rendered the bacteria secretion negative. In silico analysis of protein motifs with similar amino acid profiles revealed that this amino acid is located within a putative peptidoglycan (PG) binding motif in the periplasmic domain of ExeA. Substitution mutations of three highly conserved amino acids in the motif were constructed. In cells expressing each of these mutants, the ability to assemble the ExeD secretin or secrete aerolysin was lost, while ExeA retained the ability to form a complex with ExeB. In in vivo cross‐linking experiments, wild‐type ExeA could be cross‐linked to PG, whereas the three substitution mutants of ExeA could not. These data indicate that PG binding and/or remodelling plays a role in the function of the ExeAB complex during assembly of the ExeD secretin.