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Toxins and Type II Secretion Systems, Page 1 of 2
< Previous page Next page > /docserver/preview/fulltext/10.1128/9781555817893/9781555812454_Chap06-1.gif /docserver/preview/fulltext/10.1128/9781555817893/9781555812454_Chap06-2.gifAbstract:
The type II secretion pathway is responsible for secretion of toxins and a variety of hydrolytic enzymes that include proteases, lipases, phospholipases, cellulases, and pectinases, which contribute to tissue damage and disease of animals and plants. Cholera toxin, exotoxin A, and aerolysin produced by Vibrio cholerae, Pseudomonas aeruginosa, and Aeromonas hydrophila, respectively, are examples of three toxins that utilize the type II pathway for extracellular secretion. The biogenesis of all three toxins has been analyzed, and their crystal structures have been solved. The secretion of CT across the bacterial cell envelope occurs in two distinct steps that have different requirements; transport across the cytoplasmic membrane is followed by outer membrane translocation. A current hypothesis postulates that molecules secreted by the type II system may encode information critical to their secretion within their tertiary and quarternary structures. Restriction of proaerolysin to the poles could be evidence of periplasmic compartmentalization with concomitant secretion at the poles. The green fluorescent protein (GFP) was fused with Eps proteins to determine the cellular location, in living cells, of the type II secretion apparatus in V. cholerae. Recent intriguing data based on experiments accomplished with an active blue fluorescent protein (BFP) fused with ribosomal protein L1 in B. subtilis showed that ribosomes are located around the periphery of nucleoids, predominantly at the cell poles.