Proteins from Thermophilic Often Do Not Fold Correctly in a Mesophilic Expression System Such as .

Majority of protein structure studies use () and other model organisms as expression systems for other species' genes. However, protein folding depends on cellular environment factors, such as chaperone proteins, cytoplasmic pH, temperature, and ionic concentrations. Because of differences in these factors, especially temperature and chaperones, native proteins in organisms such as extremophiles may fold improperly when they are expressed in mesophilic model organisms. Here we present a methodology of assessing the effects of using as the expression system on protein structures. We compare these effects between eight mesophilic bacteria and (), a thermophile, and found that differences are significantly larger for . More specifically, helical secondary structures in proteins are often replaced by coil structures in . Our results show unique directionality in misfolding when proteins in thermophiles are expressed in mesophiles. This indicates that extremophiles, such as thermophiles, require unique protein expression systems in protein folding studies.