SECRETION OF PROTEINS AND ASSEMBLY OF BACTERIAL SURFACE ORGANELLES - SHARED PATHWAYS OF EXTRACELLULAR PROTEIN TARGETING

Extracellular or surface localization of virulence determinants is an important attribute of pathogenic microorganisms. The past decade has seen significant research advances in defining the steps and identifyi ng the necessary machinery for protein secretion from bacterial cells. In Gram-negative pathogens, four distinct classes of secretion pathwa ys have been identified that deliver virulence factors to their sites of action. These pathways are responsible for the delivery of soluble extracellular enzymes into the surrounding medium, or for specifically targeting proteins to the host cell. In several instances protein sec retion pathways are similar to those involved in assembly of bacterial appendage. Combination of biochemical and genetic analyses has recent ly revealed that the pathways of protein secretion and surface localiz ation of various organelles are mechanistically similar which was not apparent simply by comparing amino acid sequences of related proteins. The choice of the pathway that a protein will utilize may not be dict ated only by the specific requirement of the secreted protein to trave rse the cell envelope in the functional form, but also by the need to assure its delivery to the correct site of action outside the bacteria l cell.