Klebsiella pneumoniae pulS gene encodes an outer membrane lipoprotein required for pullulanase secretion

The product of the Klebsiella pneumoniae gene pulS, which is located downstream from the pullulanase structural gene (pulA), is essential for the cell surface localization and extracellular release of pullulanase in Escherichia coli K-12. pulS is transcribed in the opposite direction to pulA, from which it is separated by a region of 624 nucleotides. Although this latter region contains a new component of the maltose regulon, pulB, which is transcribed from the pulA promoter, it is not required for pullulanase synthesis or secretion. Unlike pulA and all other pullulanase secretion genes characterized so far, the expression of pulS is not induced by growth in the presence of maltose and is unaffected by mutations in the maltose regulator gene malT. The pulS gene product was identified as a ca. 12-kilodalton outer membrane lipoprotein. The characterization of PulS brings to three the number of identified proteins which are known to be required for pullulanase secretion in addition to the components of the signal sequence-dependent general protein export pathway.