Allostery and conformational dynamics in cAMP-binding acyltransferases [Molecular Biophysics]

April 18th, 2014 by Podobnik, M., Siddiqui, N., Rebolj, K., Nambi, S., Merzel, F., Visweswariah, S. S.

Mycobacteria harbor unique proteins that regulate protein lysine acylation in a cAMP-regulated manner. These lysine acyltransferases from Mycobacterium smegmatis (KATms) and M. tuberculosis (KATmt) show distinctive biochemical properties in terms of cAMP-binding affinity to the N-terminal cyclic nucleotide binding domain, and allosteric activation of the C-terminal acyltransferase domain. Here we provide evidence for structural features in KATms that account for high affinity-cAMP binding, and elevated acyltransferase activity in the absence of cAMP. Structure guided mutational analysis converted KATms from a cAMP-regulated to a cAMP-dependent acyltransferase, and identified a unique asparagine residue in the acyltransferase domain of KATms that assists in the enzymatic reaction in the absence of a highly conserved glutamate residue seen in GNAT-like acyltransferases. We thus have identified mechanisms by which properties of similar proteins have diverged in two species of mycobacteria by modifications in amino acid sequence, which can dramatically alter the abundance of conformational states adopted by a protein.