Dataset Information

A structural snapshot of type II pilus formation in Streptococcus pneumoniae.

ABSTRACT: Pili are fibrous appendages expressed on the surface of a vast number of bacterial species, and their role in surface adhesion is important for processes such as infection, colonization, andbiofilm formation. The human pathogen Streptococcus pneumoniae expresses two different types of pili, PI-1 and PI-2, both of which require the concerted action of structural proteins and sortases for their polymerization. The type PI-1 streptococcal pilus is a complex, well studied structure, but the PI-2 type, present in a number of invasive pneumococcal serotypes, has to date remained less well understood. The PI-2 pilus consists of repeated units of a single protein, PitB, whose covalent association is catalyzed by cognate sortase SrtG-1 and partner protein SipA. Here we report the high resolution crystal structures of PitB and SrtG1 and use molecular modeling to visualize a "trapped" 1:1 complex between the two molecules. X-ray crystallography and electron microscopy reveal that the pneumococcal PI-2 backbone fiber is formed by PitB monomers associated in head-to-tail fashion and that short, flexible fibers can be formed even in the absence of coadjuvant proteins. These observations, obtained with a simple pilus biosynthetic system, are likely to be applicable to other fiber formation processes in a variety of Gram-positive organisms.

SUBMITTER: Shaik MM

PROVIDER: S-EPMC4566232 | biostudies-literature | 2015 Sep

REPOSITORIES: biostudies-literature

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A structural snapshot of type II pilus formation in Streptococcus pneumoniae.

Shaik Md Munan MM Lombardi Charlotte C Maragno Trindade Daniel D Fenel Daphna D Schoehn Guy G Di Guilmi Anne Marie AM Dessen Andréa A

The Journal of biological chemistry 20150721 37

Pili are fibrous appendages expressed on the surface of a vast number of bacterial species, and their role in surface adhesion is important for processes such as infection, colonization, andbiofilm formation. The human pathogen Streptococcus pneumoniae expresses two different types of pili, PI-1 and PI-2, both of which require the concerted action of structural proteins and sortases for their polymerization. The type PI-1 streptococcal pilus is a complex, well studied structure, but the PI-2 typ ...[more]

PMID: 26198632

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Project description:The Streptococcus pneumoniae pilus-1 is encoded by pilus islet 1 (PI-1), which has three clonal variants (clade I, II and III) and is present in about 30% of clinical pneumococcal isolates. In vitro and in vivo assays have demonstrated that pilus-1 is involved in attachment to epithelial cells and virulence, as well as protection in mouse models of infection. Several reports suggest that pilus-1 expression is tightly regulated and involves the interplay of numerous genetic regulators, including the PI-1 positive regulator RlrA. In this report we provide evidence that pilus expression, when analyzed at the single-cell level in PI-1 positive strains, is biphasic. In fact, the strains present two phenotypically different sub-populations of bacteria, one that expresses the pilus, while the other does not. The proportions of these two phenotypes are variable among the strains tested and are not influenced by genotype, serotype, growth conditions, colony morphology or by the presence of antibodies directed toward the pilus components. Two sub-populations, enriched in pilus expressing or not expressing bacteria were obtained by means of colony selection and immuno-detection methods for five strains. PI-1 sequencing in the two sub-populations revealed the absence of mutations, thus indicating that the biphasic expression observed is not due to a genetic modification within PI-1. Microarray expression profile and western blot analyses on whole bacterial lysates performed comparing the two enriched sub-populations, revealed that pilus expression is regulated at the transcriptional level (on/off regulation), and that there are no other genes, in addition to those encoded by PI-1, concurrently regulated across the strains tested. Finally, we provide evidence that the over-expression of the RrlA positive regulator is sufficient to induce pilus expression in pilus-1 negative bacteria. Overall, the data presented here suggest that the observed biphasic pilus expression phenotype could be an example of bistability in pneumococcus.

Dataset Information

A structural snapshot of type II pilus formation in Streptococcus pneumoniae.

Publications

A structural snapshot of type II pilus formation in Streptococcus pneumoniae.

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