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Isopeptide bonds block the mechanical extension of pili in pathogenic Streptococcus pyogenes.

ABSTRACT: In the early stages of an infection, pathogenic bacteria use long fibrous structures known as pili as adhesive anchors for attachment to the host cells. These structures also play key roles in colony and biofilm formation. In all those processes, pili must withstand large mechanical forces. The pili of the nasty gram-positive human pathogen Streptococcus pyogenes are assembled as single, micrometer long tandem modular proteins of covalently linked repeats of pilin proteins. Here we use single molecule force spectroscopy techniques to study the mechanical properties of the major pilin Spy0128. In our studies, we engineer polyproteins containing repeats of Spy0128 flanked by the well characterized I27 protein which provides an unambiguous mechanical fingerprint. We find that Spy0128 is an inextensible protein, even when pulled at forces of up to 800 pN. We also found that this remarkable mechanical resilience, unique among the modular proteins studied to date, results from the strategically located intramolecular isopeptide bonds recently identified in the x-ray structure of Spy0128. Removal of the isopeptide bonds by mutagenesis readily allowed Spy0128 domains to unfold and extend, albeit at relatively high forces of 172 pN (N-terminal domain) or 250 pN (C-terminal domain). Our results show that in contrast to the elastic roles played by large tandem modular proteins such as titin and fibronectin, the giant pili of S. pyogenes evolved to abrogate mechanical extensibility, a property that may be crucial in the pathogenesis of this most virulent bacterium and, therefore, become the target of new therapeutic approaches against its infections.

SUBMITTER: Alegre-Cebollada J

PROVIDER: S-EPMC2857001 | biostudies-literature | 2010 Apr

REPOSITORIES: biostudies-literature

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Isopeptide bonds block the mechanical extension of pili in pathogenic Streptococcus pyogenes.

Alegre-Cebollada Jorge J Badilla Carmen L CL Fernández Julio M JM

The Journal of biological chemistry 20100205 15

In the early stages of an infection, pathogenic bacteria use long fibrous structures known as pili as adhesive anchors for attachment to the host cells. These structures also play key roles in colony and biofilm formation. In all those processes, pili must withstand large mechanical forces. The pili of the nasty gram-positive human pathogen Streptococcus pyogenes are assembled as single, micrometer long tandem modular proteins of covalently linked repeats of pilin proteins. Here we use single mo ...[more]

PMID: 20139067

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Project description:Streptococcus pyogenes (group A Streptococcus [GAS]) is an important human pathogen causing a broad spectrum of diseases and associated with significant global morbidity and mortality. Almost all GAS isolates express a surface hyaluronic acid capsule, a virulence determinant that facilitates host colonization and impedes phagocyte killing. However, recent epidemiologic surveillance has reported a sustained increase in both mucosal and invasive infections caused by nonencapsulated GAS, which questions the indispensable role of hyaluronic acid capsule in GAS pathogenesis. In this study, we found that pilus of M4 GAS not only significantly promotes biofilm formation, adherence, and cytotoxicity to human upper respiratory tract epithelial cells and keratinocytes, but also promotes survival in human whole blood and increased virulence in murine models of invasive infection. T4 antigen, the pilus backbone protein of M4 GAS, binds haptoglobin, an abundant human acute-phase protein upregulated upon infection and inflammation, on the bacterial surface. Haptoglobin sequestration reduces the susceptibility of nonencapsulated M4 GAS to antimicrobial peptides released from activated neutrophils and platelets. Our results reveal a previously unappreciated virulence-promoting role of M4 GAS pili, in part mediated by co-opting the biology of haptoglobin to mitigate host antimicrobial defenses.IMPORTANCE Group A Streptococcus (GAS) is a strict human pathogen causing more than 700 million infections globally each year. The majority of the disease-causing GAS are encapsulated, which greatly guarantees survival and dissemination in the host. Emergence of the capsule-negative GAS, such as M4 GAS, in recent epidemiologic surveillance alarms the necessity to elucidate the virulence determinants of these pathogens. Here, we found that M4 pili play an important role in promoting M4 GAS adherence and cytotoxicity to human pharyngeal epithelial cells and keratinocytes. The same molecule also significantly enhanced M4 GAS survival and replication in human whole blood and experimental murine infection. T4 antigen, which composes the backbone of M4 pili, was able to sequester the very abundant serum protein haptoglobin to further confer M4 GAS resistance to antibacterial substances released by neutrophils and platelets.

Dataset Information

Isopeptide bonds block the mechanical extension of pili in pathogenic Streptococcus pyogenes.

Publications

Isopeptide bonds block the mechanical extension of pili in pathogenic Streptococcus pyogenes.

Similar Datasets

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