AN INTERFACE POINT-MUTATION VARIANT OF TRIOSEPHOSPHATE ISOMERASE IS COMPACTLY FOLDED AND MONOMERIC AT LOW-PROTEIN CONCENTRATIONS

Wild-type trypanosomal triosephosphate isomerase (wtTIM) is a very tig ht dimer, The interface residue His-47 of wtTIM has been mutated into an asparagine, Ultracentrifugation data show that this variant (H47N) only dimerises at protein concentrations above 3 mg/ml, H47N has been characterised at a protein concentration,where it is predominantly a m onomer, Circular dichroism measurements in the near-UV and far-UV show that this monomer is a compactly folded protein with secondary struct ure similar as in wtTIM. The thermal stability of the monomeric H47N i s decreased compared to wtTIM: temperature gradient gel electrophoresi s (TGGE) measurements give T-m-values of 41 degrees C for wtTIM, where as the T-m-value for the monomeric form of H47N is approximately 7 deg rees C lower.