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Category: Microbial Genetics and Molecular Biology; Bacterial Pathogenesis
Type III Secretion Machinery and Effectors, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555818395/9781555813017_Chap09-1.gif /docserver/preview/fulltext/10.1128/9781555818395/9781555813017_Chap09-2.gifAbstract:
The translocated effectors harbor many different activities and can be used in different combinations by various bacteria to exert highly specific and unique effects on the host cell. Additionally, even homologous effectors with identical enzymatic activity can vary enough in substrate specificity and delivery to make their effect on the host cell tailored for a given pathogen. In understanding the biology of these systems, moderate- and high-resolution structural information has often played a key role and, furthermore, revealed aspects and themes in the pathogenesis of these systems that were much less clear from data generated from more indirect experimental techniques. This chapter represents only a skimming of the surface in examining these systems from a structural point of view, but it is nonetheless informative. Composed of more than 20 proteins and related to the flagellar assembly apparatus, type III secretion systems are one of the most complex protein secretion systems to be discovered. Rather than presenting the structures based on their fold or biochemical activity or on the species which utilize them, the chapter is organized in biological themes and examines the structures in related functional contexts. Detailed structural analyses of type III secretion virulence systems are only in their infancy. The field awaits high-resolution work on the needle complex, the translocon, the bacterial side elements, and the remaining arsenal of effector molecules used by the different gram-negative pathogens utilizing this translocation system in plants and animals.
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The type III secretion system needle complex. (A) An electron micrograph of osmotically shocked bacterial cells from S. enterica serovar Typhimurium reveals a structure with an inner membrane-associated base (white arrow), outer membrane ring, and filamentous extension (the “needle”; black arrow). Reprinted from Kubori et al. (1998) with permission. (B) Higher-resolution EM reconstructions of isolated needle complexes from Shigella reveal the details of the substructures of the secretion apparatus. The needle filament (light gray arrow), the outer membrane secretin rings (white arrow), the periplasmic rings (dark gray arrow), and the inner membrane rings (black arrow) are shown. Reprinted from Blocker et al. (2001) with permission. (C) Schematic of the needle complex, illustrating the docking of the filament with the host cell pore, the inner and outer membrane elements such as the secretin rings, periplasmic rings, and inner membrane rings. The bacterial cytoplasm contains homodimeric secretion chaperones binding to effector molecules prior to translocation through the needle complex.
The type III secretion system needle complex. (A) An electron micrograph of osmotically shocked bacterial cells from S. enterica serovar Typhimurium reveals a structure with an inner membrane-associated base (white arrow), outer membrane ring, and filamentous extension (the “needle”; black arrow). Reprinted from Kubori et al. (1998) with permission. (B) Higher-resolution EM reconstructions of isolated needle complexes from Shigella reveal the details of the substructures of the secretion apparatus. The needle filament (light gray arrow), the outer membrane secretin rings (white arrow), the periplasmic rings (dark gray arrow), and the inner membrane rings (black arrow) are shown. Reprinted from Blocker et al. (2001) with permission. (C) Schematic of the needle complex, illustrating the docking of the filament with the host cell pore, the inner and outer membrane elements such as the secretin rings, periplasmic rings, and inner membrane rings. The bacterial cytoplasm contains homodimeric secretion chaperones binding to effector molecules prior to translocation through the needle complex.