Activation of atypical protein kinase C by sphingosine 1-phosphate revealed by an aPKC-specific activity reporter.

Atypical protein kinase C (aPKC) isozymes are unique in the PKC superfamily in that they are not regulated by the lipid second messenger diacylglycerol, which has led to speculation about whether a different second messenger acutely controls their function. Here, using a genetically encoded reporter that we designed, aPKC-specific C kinase activity reporter (aCKAR), we found that the lipid mediator sphingosine 1-phosphate (S1P) promoted the cellular activity of aPKC. Intracellular S1P directly bound to the purified kinase domain of aPKC and relieved autoinhibitory constraints, thereby activating the kinase. In silico studies identified potential binding sites on the kinase domain, one of which was validated biochemically. In HeLa cells, S1P-dependent activation of aPKC suppressed apoptosis. Together, our findings identify a previously undescribed molecular mechanism of aPKC regulation, a molecular target for S1P in cell survival regulation, and a tool to further explore the biochemical and biological functions of aPKC.

Mapping the allosteric sites of the A2A adenosine receptor.

The A2A adenosine receptor (A2A AR) is a G protein-coupled receptor that is pharmacologically targeted for the treatment of inflammation, sepsis, cancer, neurodegeneration, and Parkinson's disease. Recently, we applied long-timescale molecular dynamics simulations on two ligand-free receptor conformations, starting from the agonist-bound (PDB ID: 3QAK) and antagonist-bound (PDB ID: 3EML) X-ray structures. This analysis revealed four distinct conformers of the A2A AR: the active, intermediate 1, intermediate 2, and inactive. In this study, we apply the fragment-based mapping algorithm, FTMap, on these receptor conformations to uncover five non-orthosteric sites on the A2A AR. Two sites that are identified in the active conformation are located in the intracellular region of the transmembrane helices (TM) 3/TM4 and the G protein-binding site in the intracellular region between TM2/TM3/TM6/TM7. Three sites are identified in the intermediate 1 and intermediate 2 conformations, annexing a site in the lipid interface of TM5/TM6. Five sites are identified in the inactive conformation, comprising a site in the intracellular region of TM1/TM7 and in the extracellular region of TM3/TM4 of the A2A AR. We postulate that these sites on the A2A AR be screened for allosteric modulators for the treatment of inflammatory and neurological diseases.

Investigation of the conformational dynamics of the apo A2A adenosine receptor.

The activation/deactivation processes for G-protein coupled receptors (GPCRs) have been computationally studied for several different classes, including rhodopsin, the ß2 adrenergic receptor, and the M2 muscarinic receptor. Despite determined cocrystal structures of the adenosine A2A receptor (A2A AR) in complex with antagonists, agonists and an antibody, the deactivation process of this GPCR is not completely understood. In this study, we investigate the convergence of two apo simulations, one starting with an agonist-bound conformation (PDB: 3QAK)(14) and the other starting with an antagonist-bound conformation (PDB: 3EML)(11) . Despite the two simulations not completely converging, we were able to identify distinct intermediate steps of the deactivation process characterized by the movement of Y288(7.53) in the NPxxY motif. We find that Y288(7.53) contributes to the process by forming hydrogen bonds to residues in transmembrane helices 2 and 7 and losing these interactions upon full deactivation. Y197(5.58) also plays a role in the process by forming a hydrogen bond only once the side chain moves from the lipid interface to the middle of the helical bundle.