A Universal Stress Protein (USP) in Mycobacteria binds cAMP [Protein Structure and Folding]

March 23rd, 2015 by Banerjee, A., Adolph, R. S., Gopalakrishnapai, J., Kleinboelting, S., Emmerich, C., Steegborn, C., Visweswariah, S. S.

Mycobacteria are endowed with rich and diverse machinery for the synthesis, utilization and degradation of cAMP. The actions of cyclic nucleotides are generally mediated by binding of cAMP to conserved and well-characterized cyclic nucleotide binding (CNB) domains, or structurally distinct GAF domain-containing proteins. Proteins with CNB and GAF domains can be identified in the genome of Mycobacterial species and some of them have been characterized. Here we show that a significant fraction of intracellular cAMP is bound to protein in Mycobacterial species, and using affinity chromatography techniques, identify specific universal stress proteins (USP) as abundantly expressed cAMP-binding proteins in slow-growing as well as fast growing Mycobacteria. We have characterized the biochemical and thermodynamic parameters for binding of cAMP, and show that these USPs bind cAMP with a higher affinity than ATP, an established ligand for other USPs. We determined the structure of the USP MSMEG_3811 bound to cAMP and confirmed through structure guided mutagenesis residues important for cAMP binding. This family of USPs is conserved in all Mycobacteria and we suggest that they serve as 'sinks' for cAMP, making this second messenger available for downstream effectors as and when ATP levels are altered in the cell.