Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) was synthesized and subsequently neutralized with various acids to form PDMAEMA 3 HCl, PDMAEMA 3 HBF 4 , and PDMAEMA 3 HOTf polyelectrolytes. In addition, ion exchange of the chloride anion provided polyelectrolytes with NO 3 -, N(CN) 2 -, PF 6 -, and Tf 2 N -anions. The glass transition temperature (T g ) varied significantly with anion in the order Cl -> PF 6 -> BF 4 -> NO 3 -> TfO -> Tf 2 N -. The polyelectrolytes with larger, weakly coordinated anions required less thermal energy to dissociate ionic interactions, leading to tailored thermal behavior. Solution conductivity of the water-soluble polyelectrolytes decreased in the order Cl -> NO 3 -> BF 4 -> N(CN) 2 -> TfO -, which was consistent with counteranion mobility. Solution rheology revealed polyelectrolyte behavior for PDMAEMA 3 HCl, PDMAEMA 3 HBF 4 , and PDMAEMA 3 HOTf. PDMAEMA 3 HCl underwent an electrosprayingelectrospinning transition at three times the critical concentration for entanglement (C e ), which was consistent with other cationic polyelectrolytes. However, the BF 4 -and TfO -polyelectrolytes exhibited an onset of fiber formation at (1.4-1.8)C e , much closer to the behavior of neutral, nonassociating polymers. Fiber diameters for all polyelectrolytes were 1-2 orders of magnitude smaller than those for neutral polymers due to increased conductivities of the electrospinning solutions.

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Cyclic nucleotide-binding (CNB) domains allosterically regulate the activity of proteins with diverse functions, but the mechanisms that enable the cyclic nucleotide-binding signal to regulate distant domains are not well understood. Here we use optical tweezers and molecular dynamics to dissect changes in folding energy landscape associated with cAMP-binding signals transduced between the two CNB domains of protein kinase A (PKA). We find that the response of the energy landscape upon cAMP binding is domain specific, resulting in unique but mutually coordinated tasks: one CNB domain initiates cAMP binding and cooperativity, whereas the other triggers inter-domain interactions that promote the active conformation. Inter-domain interactions occur in a stepwise manner, beginning in intermediate-liganded states between apo and cAMP-bound domains. Moreover, we identify a cAMP-responsive switch, the N3A motif, whose conformation and stability depend on cAMP occupancy. This switch serves as a signaling hub, amplifying cAMP-binding signals during PKA activation.