Transport of hemolysin by Escherichia coli

Abstract

The hemolytic phenotype in Escherichia coli is determined by four genes. Two (hlyC and hlyA) determine the synthesis of a hemolytically active protein which is transported across the cytoplasmic membrane. The other two genes (hlyBa and hlyBb) encode two proteins which are located in the outer membrane and seem to form a specific transport system for hemolysin across the outer membrane. The primary product of gene hlyA is a protein (protein A) of 106,000 daltons which is nonhemolytic and which is not transported. No signal peptide can be recognized at its N‐terminus. In the presence of the hlyC gene product (protein C), the 106,000‐dalton protein is processed to the major proteolytic product of 58,000 daltons, which is hemolytically active and is transported across the cytoplasmic membrane. Several other proteolytic fragments of the 106,000‐dalton protein are also generated. During the transport of the 58,000‐dalton fragment (and possible other proteolytic fragments of hlyA gene product), the C protein remains in the cytoplasm. In the absence of hlyBa and hlyBb the entire hemolytic activity (mainly associated with the 58,000‐dalton protein) is located in the periplasm: Studies on the location of hcmolysin in hlyBa and hlyBb mutants suggest that the gene product of hlyBa (protein Ba) binds hemolysin and leads it through the outer membrane whereas the gene product of hlyBb (protein Bb) releases hemolysin from the outer membrane. This transport system is specific for E coli hemoiysin. Other periplasmic enzymes of E coli and heterologous hemolysin (cereolysin) are not transported.

Molecular Analysis of Bacterial Cytolysins

“…C-terminal end of HlyA, as suggested by previous data [13], or that the transport system (HlyB and HlyD) is recognized only by HlyA in its intact conformation. Recent data show that extracellular hemolysin is extremely sensitive to lipase treatment (figure 1).…”

Release of a chimeric protein into the medium from Escherichia coli using the C-terminal secretion signal of haemolysin.

“…In contrast, colicins are produced from cells which eventually lyse (Pugsley and Schwartz, 1984;Cavard et al, 1985) due to changes in the structure of the outer membrane. The HlyA protein lacks a classical N-terminal signal sequence (Hartlein et al, 1983;Fehmlee et al, 1985a) and is secreted efficiently in secA' mutants grown at the restrictive temperature (unpublished data); conditions in which the export of many envelope proteins is blocked. Therefore, the secretion of HlyA per se does not appear to use the normal secA dependent pathway in E. coli to cross the inner membrane.…”

Characterisation of HlyC and mechanism of activation and secretion of haemolysin from E. coli 2001

“…A 3 kb region encoding hlyC and h/yA determines the synthesis of a haemolytically active protein whilst a contiguous 4 kb region encodes hlyB and hlyD (nomenclature adopted from [ 11, corresponding to hlyBa and hlyBb, respectively) which are essential for export of the haemolysin to the culture medium [2-41. Goebel and co-workers [5] proposed that the hlyC gene is involved in a proteolytic cleavage of the 107 kDa polypeptide encoded by hlyA and the concomitant transport of a haemolytically active 58 kDa derivative across the inner membrane. From the periplasm, it was proposed that this protein is then transported across the outer membrane by the export functions encoded by hlyB and hlyD.…”