The Bacillus subtilis lipoprotein LplA causes cell lysis when expressed in Escherichia coli

A gene called lplA (lipoprotein-like) has been isolated from a genomic library of Bacillus subtilis expressed in Escherichia coli. Clones carrying the lplA gene were selected by the ability of the colonies to give visible haloes of starch hydrolysis. The cloned fragment contains an open reading frame (ORF) of 1509 bp encoding a protein of 56 kDa. The protein contains a typical N-terminal signal sequence, a putative transmembrane anchor domain and a leucine zipper at the C-terminus. The expression of this protein in E. coli causes cell lysis, only the N-terminal domain of the LplA protein being responsible for this phenotype. The mechanism of cell lysis is similar to that previously suggested for the expression in E. coli of the lipoproteins encoded by the Streptococcus pneumoniae genes malX and amiA. The protein is modified with palmitic acid when secreted in E. coli, confirming that it is a typical lipoprotein.