A synthetic peptide that prevents cAMP regulation in mammalian hyperpolarization-activated cyclic nucleotide-gated (HCN) channels

Binding of TRIP8b to the cyclic nucleotide binding domain (CNBD) of mammalian hyperpolarization-activated cyclic nucleotide-gated (HCN) channels prevents their regulation by cAMP. Since TRIP8b is expressed exclusively in the brain, we envisage that it can be used for orthogonal control of HCN channels beyond the central nervous system. To this end, we have identified by rational design a 40-aa long peptide (TRIP8b(nano)) that recapitulates affinity and gating effects of TRIP8b in HCN isoforms (hHCN1, mHCN2, rbHCN4) and in the cardiac current I(f) in rabbit and mouse sinoatrial node cardiomyocytes. Guided by an NMR-derived structural model that identifies the key molecular interactions between TRIP8b(nano) and the HCN CNBD, we further designed a cell-penetrating peptide (TAT-TRIP8b(nano)) which successfully prevented β-adrenergic activation of mouse I(f) leaving the stimulation of the L-type calcium current (I(CaL)) unaffected. TRIP8b(nano) represents a novel approach to selectively control HCN activation, which yields the promise of a more targeted pharmacology compared to pore blockers.