The Role of Streptococcal Cell-Envelope Proteases in Bacterial Evasion of the Innate Immune System.

Bacteria possess the ability to evolve varied and ingenious strategies to outwit the host immune system, instigating an evolutionary arms race. Proteases are amongst the many weapons employed by bacteria, which specifically cleave and neutralize key signalling molecules required for a coordinated immune response. In this article, we focus on a family of S8 subtilisin-like serine proteases expressed as cell-envelope proteases (CEPs) by group A and group B streptococci. Two of these proteases known as Streptococcus pyogenes CEP (SpyCEP) and C5a peptidase cleave the chemokine CXCL8 and the complement fragment C5a, respectively. Both CXCL8 and C5a are potent neutrophil-recruiting chemokines, and by neutralizing their activity, streptococci evade a key defence mechanism of innate immunity. We review the mechanisms by which CXCL8 and C5a recruit neutrophils and the characterization of SpyCEP and C5a peptidase, including both in vitro and in vivo studies. Recently described structural insights into the function of this CEP family are also discussed. We conclude by examining the progress of prototypic vaccines incorporating SpyCEP and C5a peptidase in their preparation. Since streptococci-producing SpyCEP and C5a peptidase are responsible for a considerable global disease burden, targeting these proteases by vaccination strategies or by small-molecule antagonists should provide protection from and promote the resolution of streptococcal infections.

Rif1 phosphorylation site analysis in telomere length regulation and the response to damaged telomeres.

Telomeres, the ends of eukaryotic chromosomes, consist of repetitive DNA sequences and their bound proteins that protect the end from the DNA damage response. Short telomeres with fewer repeats are preferentially elongated by telomerase. Tel1, the yeast homolog of human ATM kinase, is preferentially recruited to short telomeres and Tel1 kinase activity is required for telomere elongation. Rif1, a telomere-binding protein, negatively regulates telomere length by forming a complex with two other telomere binding proteins, Rap1 and Rif2, to block telomerase recruitment. Rif1 has 14 SQ/TQ consensus phosphorylation sites for ATM kinases, including 6 in a SQ/TQ Cluster Domain (SCD) similar to other DNA damage response proteins. These 14 sites were analyzed as N-terminal, SCD and C-terminal domains. Mutating some sites to non-phosphorylatable residues increased telomere length in cells lacking Tel1 while a different set of phosphomimetic mutants increased telomere length in cells lacking Rif2, suggesting that Rif1 phosphorylation has both positive and negative effects on length regulation. While these mutations did not alter the sensitivity to DNA damaging agents, inducing telomere-specific damage by growing cells lacking YKU70 at high temperature revealed a role for the SCD. Mass spectrometry of Rif1 from wild type cells or those induced for telomere-specific DNA damage revealed increased phosphorylation in cells with telomere damage at an ATM consensus site in the SCD, S1351, and non-ATM sites S181 and S1637. A phosphomimetic rif1-S1351E mutation caused an increase in telomere length at synthetic telomeres but not natural telomeres. These results indicate that the Rif1 SCD can modulate Rif1 function. As all Rif1 orthologs have one or more SCD domains, these results for yeast Rif1 have implications for the regulation of Rif1 function in humans and other organisms.