Identification of an essential backbone amide bond in the folding and stability of a multimeric enzyme
Here we utilize a total chemical synthesis strategy and a mass spectrometry-based, combinatorial chemistry approach to identify key molecular interactions that contribute to the folding and stability of a model multimeric enzyme, 4-oxalocrotonate tautomerase (4OT). 4OT is a 41 kDa bacterial enzyme composed of six identical 62 amino acid subunits. A total of 16 different 4OT analogues containing various natural and unnatural N-terminal modifications were prepared by total chemical synthesis and then characterized by catalytic activity, size exclusion chromatography (SEC), and circular dichroism (CD) spectroscopy. The results of our mutational studies indicate that backbone - backbone hydrogen-bonding interactions involving the amide bond between Pro1 and Ile2 in 4OT's 62 amino acid polypeptide chain play an important role in specifying the conformation of this enzyme's native folded state. These results provide the first evidence that backbone -backbone hydrogen-bonding interactions can play such a major role in specifying the native state of a protein.