BPS2026 – All-atom simulations reveal cationic peptide activation of the bradykinin type 2 receptor

The bradykinin type 2 receptor (BK2R), a class A G protein-coupled receptor (GPCR), is vital in inflammation and pain responses, with elevated expression linked to chronic pain post-spinal injury. Dynorphin A (Dyn), a cationic opioid peptide primarily associated with the kappa opioid receptor, has been implicated as a hyperalgesic in this context. Dyn exhibits opioid receptor-independent activity, and certain variants of Dyn interact with BK2R, suggesting a role in this receptor and ligand for sustaining chronic pain. However, the molecular mechanisms underlying these interactions remain unclear. Additionally, the presence of an anion trap in BK2R raises the question whether other cationic peptides can similarly sustain chronic pain. To investigate, we performed unbiased all-atom molecular dynamics simulations on BK2R with ligands Dyn 2-17 (+4), an opioid receptor independent variant, HIV-TAT (+8), and penetratin (+7), generating > 35.6 μs of aggregate trajectory data. Our MD simulations reveal stabilizing salt bridges between the receptor and ligand, and outward displacements of the cytoplasmic ends of transmembrane helices (TM) 6 and 7 of BK2R following binding, consistent with class A GPCR activation. Ligand density analysis identifies predicted binding sites: Dyn and TAT engage the entrance of the orthosteric binding pocket near extracellular loop 2 (ECL2) and TM7, while penetratin interacts with the exterior of BK2R. Principal component analysis reveals the large-scale rearrangements in TMs 1-3, with additional shifts in TM4 and ECL2. Quantitative analysis shows that Dyn and TAT drive conformational transitions in the first five principal components that reflect GPCR activation, whereas penetratin’s size, solvation structure, and rigidity limit productive binding and efficacy. Overall, these findings demonstrate cationic peptides can not only activate BK2R but also underscore the importance of the analysis of intrinsic ligand properties in determining their ability to achieve GPCR activation.