Chaperones trigger factor

The discoveries of Csp s and trigger factor may represent the tip of a large iceberg. In view of the pervasive effects of low temperature on the structures of all classes of macromolecules, it is reasonable to conjecture that many more types of proteins will be discovered whose roles are to offset the effects of cold shock on the cell. Some of these molecules may be expressed constitutively and may be part of the normal machinery of the cell. For example, certain ribosomal proteins are thought to function as RNA chaperones, and if present in sufficient amounts, these proteins may allow the cell to cope with the effects of cold shock on the structures of certain classes of RNAs. In yeast, a constitutively expressed ribosomal protein has helicase activity, and mutation in the gene encoding the protein confers on the cells a cold-sensitive phenotype (Schmid and Linder, 1992). Perhaps the apparent absence of cold-induced RNA chaperones in eukaryotic cells is... 

There is evidence that the trigger factor and the hsp70 chaperone DnaK, a PPIase and a secondary amide peptide bond cis-trans isomerase (APIase) respectively, contribute to the formation of native proteins by apparently overlapping functions with the trigger factor as the primary interaction partner of the emerging polypeptide chain [122-124]. Consequently, synthetic lethality was observed... 

Recombinantly produced DnaK was utilized to characterize its APIase function enzymatically. Co-chaperones, such as DnaJ and GrpE in the presence of ATP might contribute to create the subsite specificity of DnaK. For oligopeptide substrates, the APIase function of DnaK does not require concomitant ATP hydrolysis. A functional overlap of a PPIase and an APIase, trigger factor and DnaK, respectively, could not be observed in an APIase and a standard PPIase assay [127]. Generally, PPIases fail to accelerate CTI of secondary amide peptide bonds in peptide substrates and folding intermediates [152]. 

Teter SA, Houry WA, Ang D, Tradier T, Rockabrand D, Fischer G, Blum P, Georgopoulos C, Hartl FU (1999) Polypeptide flux through bacterial HspVO DnaK cooperates with trigger factor in chaperoning nascent chains. Cell 97 755-765... 

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