labile in most mesophilic microorganisms, but dimeric and stable in the hyperthermophile Thermotoga maritima (tPRAI). [ 2 ] The comparison to the known 2.0 A structure of PRAI from Escherichia coli (ePRAI) shows that tPRAI has a TIM-barrel fold, whereas helix alpha5 in ePRAI is replaced by a loop . The