El virus Sulfolobus Spindle-shaped virus 8 (SSV8) actúa como factor de estrés en Sulfolobus solfataricus P2 y regula al alza la producción de proteínas de choque térmico (HSP)

Abstract

Heat shock proteins (HSPs) are present in Archaea, Bacteria and Eukarya organisms and are highly regulated in response to stress due to temperature increase. In addition, they are responsible for the folding of synthesized proteins and refolding of misfolded or denatured proteins thus having a regulatory function of protein balance in the cell. In the Archaea domain these chaperonins are called Archaeal group II and are among the most abundant expressed proteins in sulfolobales. HSP complexes are non-americ double stranded octadecameric structures composed of one or more subunits: HSPα, HSPβ and HSPγ. Under heat shock stress conditions, HSPα and HSPβ are the main subunits involved in complex formation and function. In this research we studied the consequences of stress by viral infection in organisms of the genus Sulfolobus, taking Sulfolobus Solfataricus strain P2 as host model and Sulfolobus SpindleShape Virus 8 SSV8 (a.k.a SSVRH) as the viral agent, seeking to determine whether HSP expression is regulated by SSV infection. Using methods in rt-qPCR, gel electrophoresis and protein quantification (Bradford assay). The data indicate that under physiological optimal growth temperature of 76 °C, expression of both HSPα and HSPβ was similar; however, under heat shock conditions (85 °C for 30 min), HSPβ expression was observed at higher concentrations than HSPα and physiological control HSPβ (76 °C). At 76 °C and 24 h post infection (HPI) with SSV8, both HSP subunits were observed to be at a lower intracellular concentration than uninfected controls. After 48 HPI with SSV8 at 76 °C, the expression of both HSP subtypes was equivalent to uninfected controls at the same physiological temperature. Considering that there are fewer live cells at a certain time after infection (vs. uninfected controls), the equivalent HSP concentration suggests that there is a positive regulation of HSP expression during infection at 76 ° C, emphasizing a high ratio of HSPβ over HSPα genes. Based on these first reported results, Sulfolobus solfataricus strain P2 responds to SSV8 infection by up-regulating HSP expression under both physiological and heat shock conditions. Overall, these data suggest that group II chaperonins and HSP complexes have a role in the dynamics of host SSV infection. The sudden drop in HSP expression at the beginning of infection dynamics suggests that host metabolic resources have been redirected; however, further along in the infection cycle, cellular HSP expression recovers. It remains to be examined whether HSP complexes protect native proteins during SSV infection or assist in the folding of viral proteins. Therefore, it can also be suggested that the increase in HSPs after SSV infection is the response to the increase of viral proteins in the Sulfolobus cytoplasm, which could be identified as a possible excess of cell proteins, thus activating the protein regulatory function of HSPs to maintain the protein balance of the host, although this should be the subject of further investigations.