Characterization of ClpS2, an essential adaptor protein for the cyanobacterium Synechococcus elongatus

Abstract

a b s t r a c tThe adaptor protein ClpS associates to the Clp protease and promotes degradation of N-end rule substrates in eubacteria and in algal/plant chloroplasts. Cyanobacteria are unusual in having two distinct ClpS paralogs. Although ClpSl is typical of bacterial ClpS, ClpS2 differs in crucial ways. ClpS2 in Synechococcus elongatus is a relatively low-abundant, soluble protein essential for phototrophic growth. Like ClpSl, ClpS2 binds to the ClpCP3/R protease to block a-casein degradation and promote that of N-end rule substrates in vitro. However, their substrate specificity differs, with ClpSl recognizing destabilizing Phe and Tyr residues at the substrate N-terminus whereas ClpS2 recognizes Leu.Overall, ClpS2 appears to have independently evolved in cyanobacteria to degrade a particular group of proteins, whose turnover is vital for cell viability.

N‐degron specificity of chloroplast ClpS1 in plants

“…The chloroplast Clp proteolytic system plays an essential role in chloroplast biogenesis, proteostasis, and metabolism . Many α‐proteobacteria such as Agrobacterium tumefaciens and cyanobacteria such as S. elongatus contain two ClpS homologs, ClpS1 similar to bacterial ClpS, and the more divergent ClpS2 . Plants contain at least one ClpS1 and in some plant species also a ClpS1‐like homolog .…”

The N‐end rule adaptor protein ClpS from Plasmodium falciparum exhibits broad substrate specificity

“…3B). Consistently, Synechococcus elongates was recently shown to contain two ClpS paralogues (ClpS1 and ClpS2), both of which exhibit different substrate specificity; ClpS1 was unable to recognise N-terminal Leu, while ClpS2 was unable to recognise N-terminal Phe or Tyr [34]. Likewise, Agrobacterium tumefaciens also contain two ClpS paralogues and similar to S. elongates, AtClpS1 exhibits broad specificity, while AtClpS2 exhibits strong binding to N-terminal Phe and no binding to N-terminal Leu [35].…”

“…3C). Consistently, Synechococcus elongates was recently shown to contain two ClpS paralogues (ClpS1 and ClpS2), both of which exhibit different substrate specificity; ClpS1 was unable to recognise N-terminal Leu, while ClpS2 was unable to recognise N-terminal Phe or Tyr [34]. However, in comparison to the bacterial N-recognins, PfClpS appears to exhibit distinct affinity for each of the different primary destabilising residues.…”

Mycobacterium tuberculosis ClpC1 N-Terminal Domain Is Dispensable for Adaptor Protein-Dependent Allosteric Regulation

“…B. subtilis ClpCP can also bind and degrade phosphoarginine substrates independent of any adaptor protein [ 16 ], thereby demonstrating that MecA association is not always required for ClpCP function as once thought. In contrast, ClpC proteins from cyanobacteria and actinobacteria are not widely known to possess chaperone activities that are adaptor protein-dependent [ 17 , 18 , 19 , 20 , 21 ]. All available data describing actinobacterial ClpC protein function have been collected using Mycobacterium tuberculosis ( M. tuberculosis ) ClpC1 (ClpC2 lacks identifiable motifs associated with ATPase activity) and demonstrate adaptor protein-independent activity.…”

“…All available data describing actinobacterial ClpC protein function have been collected using Mycobacterium tuberculosis ( M. tuberculosis ) ClpC1 (ClpC2 lacks identifiable motifs associated with ATPase activity) and demonstrate adaptor protein-independent activity. However, the protein degradation activity of Synechoccus elongatus ClpCP3/R is regulated by two ClpS isoforms, ClpS1 and ClpS2, where ClpS1 promotes the binding of N-degron protein substrates bearing N-terminal Phe and Tyr residues and ClpS2 blocks degradation of α-casein substrates [ 18 ]. No data has been reported regarding adaptor protein-dependent regulation of Clp protease complexes in actinobacteria.…”