หน้าหลัก

Milar to canonical SecYEG, SecY2 forms a channel for translocation of Milar to canonical SecYEG, SecY2 forms a channel for translocation of the Hsa adhesin across the cytoplasmic membrane. Accessory Sec proteins Asp4 and Asp5 have been Tenidap COX suggested to work alongside SecY2 to form the translocon, similar to the associated SecY, SecE, and SecG of the canonical system (SecYEG). To test this theory, S. gordonii secY2, asp4, and asp5 were co-expressed in Escherichia coli. The resultant complex was subsequently purified, and its composition was confirmed by mass spectrometry to be SecY2-Asp4-Asp5. Like SecYEG, the non-canonical complex activates the ATPase activity of the SecA motor (SecA2). This study also shows that Asp4 and Asp5 are necessary for optimal adhesion of S. gordonii to glycoproteins gp340 and fibronectin, known Hsa binding partners, as well as for early stage biofilm formation. This work opens new avenues for understanding the structure and function of the accessory Sec system.Streptococcus gordonii is part of the viridans streptococci group along with Streptococcus salivarius, Streptococcus mitis, Streptococcus mutans, Streptococcus oralis, Streptococcus parasanguinis and Streptococcus sanguinis. Together, they form an important part of the microbiota of the human oral cavity (1). These organisms colonize tooth surfaces, developing complex microbial communities and forming biofilms, also known as dental plaque, which is strongly associated with dental caries and gum disease (2). S. gordonii can initiate bacterial colonization by creating surfaces for other bacteria to adhere to (3). If oral trauma occurs, S. gordonii, and other viridans streptococci, can enter the bloodstream, leading to bacterial binding of* This work supported by Biotechnology and Biological Sciences ResearchCouncil Project Grant BB/I008675/1 (to I. C.), Medical Research Council Doctoral Training Grant 2011-G1001606 (to M. B.), Biotechnology and Biological Sciences Research Council South West Bioscience Doctoral Training Partnership (to R. A. C.), and University of Bristol postgraduate scholarship (to R. M.). The authors declare that they have no conflicts of interest with the contents of this article. Author's Choice--Final version free via Creative Commons CC-BY license. S This article contains supplemental Figs. S1 4 and Tables S1 and S2. 1 To whom correspondence should be addressed. Tel.: 44-117-342-4358; E-mail: [email protected] platelets and formation of vegetations at cardiac sites. This gives rise to damage and dysfunction of the heart valves, characteristic of infective endocarditis (4). S. gordonii DL1 expresses a number of surface proteins linked with colonization and virulence, including antigen I/II proteins (SspA and SspB) (5), fibronectin-binding proteins (CshA and CshB) (6), and serine-rich repeat glycoprotein Hsa (7). Hsa is characterized as a sialic acid-binding adhesin and hemagglutinin that has been shown to mediate binding of S. gordonii to sialylated carbohydrate structures on human platelets and salivary glycoproteins (7, 8). Hsa, and homolog GspB, has also been shown to be involved in forming biofilms and oral colonization by S. gordonii (7?). Most proteins expressed on the S. gordonii surface are transported by the general Sec pathway, but S. gordonii also contains a specialized export system seemingly dedicated to the transport of Hsa, known as the accessory Sec system (10). The core components of the accessory Sec system are SecA2 and SecY2 (homologs of general Sec proteins SecA and Se.