Abstract
Adaptation of microorganisms to low temperatures remains to be fully elucidated. It has been previously reported that peptidyl prolyl cis-trans isomerases (PPIases) are involved in cold adaptation of various microorganisms whether they are hyperthermophiles, mesophiles or phsycrophiles. The rate of cis-trans isomerization at low temperatures is much slower than that at higher temperatures and may cause problems in protein folding. However, the mechanisms by which PPIases are involved in cold adaptation remain unclear. Here we used FK506-binding protein 22, a cold shock protein from the psychrophilic bacterium Shewanella sp. SIB1 (SIB1 FKBP22) as a model protein to decipher the involvement of PPIases in cold adaptation. SIB1 FKBP22 is homodimer that assumes a V-shaped structure based on a tertiary model. Each monomer consists of an N-domain responsible for dimerization and a C-catalytic domain. SIB1 FKBP22 is a typical cold-adapted enzyme as indicated by the increase of catalytic efficiency at low temperatures, the downward shift in optimal temperature of activity and the reduction in the conformational stability. SIB1 FKBP22 is considered as foldase and chaperone based on its ability to catalyze refolding of a cis-proline containing protein and bind to a folding intermediate protein, respectively. The foldase and chaperone activites of SIB1 FKBP22 are thought to be important for cold adaptation of Shewanella sp. SIB1. These activities are also employed by other PPIases for being involved in cold adaptation of various microorganisms. Despite other biological roles of PPIases, we proposed that foldase and chaperone activities of PPIases are the main requirement for overcoming the cold-stress problem in microorganisms due to folding of proteins.
Highlights
Temperature has been deemed one of the most important factors for growth and modulates selection and distribution of microorganisms throughout the Earth
Previous studies have reported that peptidyl prolyl cis-trans isomerases (PPIases) are involved in cold adaptation of various organisms as part of their cold shock responses and adaptive mechanisms
We used SIB1 FKBP22 as a model protein, which was involved in the cold-shock responses of Shewanella sp
Summary
Catalyze cis-trans isomerization of Xaa-Pro peptide bonds (Figure 1) and assist proteins to achieve correct native conformations Due to this ability, PPIases are considered to be foldases, together with protein disulfide isomerases (PDI) [13,14]. Foldases and chaperones have been classified as CSPs, which are important for overcoming a series of problems in protein folding at low temperatures, including slow cis-trans isomerization [1]. SIB1 FKBP22 is thought to have dual functions, since it exhibits PPIase activity (foldase) and is able to bind to a folding intermediate protein (chaperone). SIB1 is an appropriate model to decipher the mechanisms for cold-adaptation To achieve this goal, we have studied several proteins isolated from Shewanella sp. This figure was reproduced and modified from Kato et al [27]
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