Study On The Mechanism Of HtpsC And Host Extracellular Matrix Of Streptococcus Suis

Streptococcus suis （S. suis） is an important Gram-positive pathogen, which can infect pigs and human and induces a wide range of serious diseases. To date, thirty-five serotypes （types 1/2, and 1-34） of S. suis have been described. Among them, Streptococcus suis serotype 2 （S. suis 2） is the most frequently isolated and associated with disease. Recently, cases of S. suis 2 infections have been reported in many countries. In particular, two large-scale outbreaks of human S.suis 2 epidemics in China in 1998 and 2005, are featured clinically with streptococcal toxic shock-like syndrome（STSLS）, which have not only caused great economic loss in the world pig industry, but also greatly challenged global public health. Therefore, it has a great significance of studying S. suis 2 infection, aiming at the prevention and control of S. suis 2 pathogenesis. To date, it’s unclear about pathogenic molecular mechanism of S. suis infection and invasion host. Therefore, further exploring the mechanism of the interactions between S. suis 2 virulence factors and host is urgently needed.Histidine triad proteins （Htp） is a novel surface-exposed proteins family ep onymied by containing multiple conserved and repeated histidine triad motif （H is-x-x-His-x-His）, which is widely distributed within the streptococcus genus. S o far, all members of Htp family found are encoded by streptococci pathogenic genes. Based on the phylogenetic relationship and composition analysis, Htps are classified into type â…  and type â…¡ subfamilies. HtpsC in S.suis 2 and itshom ologs reported in S.pyogenes and S.agalactiae, which are respectively termed Sl r and Blr, are belongs to Htpâ…¡ subfamily. They have a typical sequence charac teristic, namely at the C-terminal half occupied by the conserved LRR repeate d domain and the N-terminal occupied by the conserved HTP domain. Ithas be en demonstrated that Sir and Blr were defined a family of Listeria monocytoge nes internalin A-related streptococcal LRR proteins. And also, Sir was reported to bind to human type â…  collagen, which implys us that Htpsâ…¡ subfamily prot eins maybe interact with host ECM components and cause different diseases. I n the previous researches, HtpsC has been identified to be an important virulen ce factor for S.suis 2, involving in its pathogenicity, adherence to andinvasion host cells and tissues. In general, bacterial adherence to and invasionhost is accomplished through interactions between bacterial cell-surface adhesinsand hos t extracellular matrix （ECM） components, which is common mechanism during this process. However, to date, there are no researches about the mechanism of interactions between HtpsC in S.suis 2 and host extracellular matrix （ECM） co mponents.On the basis of analysis of HtpsC sequence encoded by the orf SSU05₁5 77 from the whole genome of S. suis 2 Chinese high virulent strain 05ZYH33, the present study identified that HtpsC is comprised of four HTP motifs at the N-terminal region and thirteen successively appearing LRR repeats at the C-ter minal. Recombinant HtpsC was eukaryotic expressed and purified. The interacti ons of HtpsC with host ECMs suggested that HtpsC is an novel surface adhesi n for S.suis 2 and a fibronectin- and laminin-binding protein, which functions as to mediate S.suis 2 to adhere to host during infection. Further recombinant rHTP and rLRR proteins were expressed and purified in vitro and their interact ions with host ECMs suggested that the N-terminal HTP domain of HtpsC is a laminin-binding protein, while the C-terminal LRR domain of HtpsC is a fibro nectin-binding protein, which mediated S.suis 2 to respectively adhere to host 1 aminin and fibronectin. In addition, adherence of S.suis 2 to fibronectin and la minin demonstrated that compared to the parent strain, the binding of â–³htpsC t o Fn and Lm decreased about 40% and 30% of that in the parent strain.In summary, our present findings identified that HtpsC of S. suis 2 05ZYH33, was an novel adhesin of S.suis 2 and a fibronectin- and laminin-binding protein, which acted as a bridge between bacteria and host fibronectin and laminin during bacteria infection and invasion to host. Further researches demonstrated that its N-terminal HTP domain is a laminin-binding protein, while its C-terminal LRR domain is a fibronectin-binding protein, which respectively mediated HtpsC to adhere to host laminin and fibronectin during S.suis 2 infection.