The leucine zipper of Aeromonas salmonicida AbcA is required for the transcriptional activation of the P2 promoter of the surface‐layer structural gene, vapA, in Escherichia coli

Abstract

The Aeromonas salmonicida AbcA protein is involved in the synthesis of the O-polysaccharide side-chains on the lipopolysaccharide and is also capable of enhancing the expression of the structural gene for the A-layer, vapA, when cloned into Escherichia coli. The P2 promoter of the vapA gene of A. salmonicida was cloned into a promoter probe vector and expression in E. coli was monitored. The expression of P2::lacZ was shown to be increased when abcA was provided in trans. AbcA contains an N-terminal ATP-binding domain as well as a C-terminal leucine zipper domain. Site-directed mutagenesis has been used to show that the ATP-binding domain is required for the synthesis of the O-polysaccharide side-chains, but not for the enhancement of vapA expression. Conversely, the leucine zipper is needed for the increase in vapA expression, but not for O-polysaccharide side-chain synthesis. This indicates that AbcA is a bifunctional protein that can influence the synthesis of the two principle antigenic components of the A. salmonicida cell surface.

A molecular approach to understanding the pathogenesis of : relevance to vaccine development

“…A recent study has determined that this activation of vapA expression in E. coli occurs at the level of transcription A. SALMONICIDA PATHOGENESIS (Noonan & Trust, 1995b). The abcA alleles which had single base mutations in the ATP-binding domain a#ecting O-chain synthesis and secretion, were still able to increase the expression of the vapA gene.…”

S-Layer Proteins

“…Further, it could be demonstrated that AbcA is a bifunctional protein in which the Nterminal part regulates the synthesis of the O-polysaccharide side chains of the LPS, functioning as a binding site for the VapA protein. The C-terminal leucine zipper increases expression of the vapA gene and can thus be considered as a transcriptional activator of the P2 promoter (25,95,96).…”

ABC Transporters Involved in Export of Cell Surface Glycoconjugates

“…This bacterium produces homogenous (nonmodal) O-PS chain lengths (22), and the NBD protein (AbcA) is required for O-PS export (24). AbcA also contains an extended C-terminal domain that contains a putative leucine zipper, which is not essential for O-PS export but is required for proper transcription of the surface layer protein gene vapA (25,100). Conversely, the activity of the core NBD portion of AbcA is confined to O-PS export.…”