Investigation into the Interactions between Diadenosine 5‘,5‘ ‘‘-P 1,P 4-Tetraphosphate and Two Proteins:  Molecular Chaperone GroEL and cAMP Receptor Protein

Diadenosine 5‘,5‘ ‘‘-P 1,P 4-tetraphosphate (Ap4A) is a dinucleoside polyphosphate found ubiquitously in eukaryotic and prokaryotic cells. Despite Ap4A being universal, its functions have proved to be difficult to define, although they appear to have a strong presence during cellular stress. Here we report on our investigations into the nature and properties of putative Ap4A interactions with Escherichia coli molecular chaperone GroEL and cAMP receptor protein (CRP). We confirm previous literature observations that GroEL is an Ap4A binding protein and go on to prove that binding of Ap4A to GroEL involves a set of binding sites (one per monomer) distinct from the well-known GroEL ATP/ADP sites. Binding of Ap4A to GroEL appears to enhance ATPase rates at higher temperatures, encourages the release of bound ADP, and may promote substrate protein release through differential destabilization of the substrate protein−GroEL complex. We suggest that such effects should result in enhanced GroEL/GroES chaperoning activities that could be a primary reason for the improved yields of the refolded substrate protein observed during GroEL/GroES-assisted folding and refolding at ≥30 °C in the presence of Ap4A. In contrast, we were unable to obtain any data to support a direct role for Ap4A interactions with CRP.