Anionic phospholipids control mechanisms of GPCR-G protein recognition

G protein-coupled receptors (GPCRs) are embedded in phospholipids that strongly influence drug-stimulated signaling. Anionic lipids are particularly important for GPCR signaling complex formation, but a mechanism for this role is not understood. Using NMR spectroscopy, we explore the impact of anionic lipids on the function-related conformational equilibria of the human A2A adenosine receptor (A2AAR) in bilayers containing defined mixtures of zwitterionic and anionic phospholipids. Anionic lipids prime the receptor to form complexes with G proteins through a conformational selection process. Without anionic lipids, signaling complex formation proceeds through a less favorable induced fit mechanism. In computational models, anionic lipids mimic interactions between a G protein and positively charged residues in A2AAR at the receptor intracellular surface, stabilizing a pre-activated receptor conformation. Replacing these residues strikingly alters the receptor response to anionic lipids in experiments. High sequence conservation of the same residues among all GPCRs supports a general role for lipid-receptor charge complementarity in signaling.

Anionic Phospholipids Control Mechanisms of GPCR-G Protein Recognition

G protein-coupled receptors (GPCRs) are embedded in phospholipids that strongly influence drug-stimulated signaling. Anionic lipids are particularly important for GPCR signaling complex formation, but a mechanism for this role is not understood. Using NMR spectroscopy, we visualized the impact of anionic lipids on the function-related conformational equilibria of the human A 2A adenosine receptor (A 2A AR) in bilayers containing defined mixtures of zwitterionic and anionic phospholipids. Anionic lipids primed the receptor to form complexes with G proteins through a conformational selection process. Without anionic lipids, signaling complex formation proceeded through a less favorable induced fit mechanism. In computational models, anionic lipids mimicked interactions between a G protein and positively charged residues in A 2A AR at the receptor intracellular surface, stabilizing a pre-activated receptor conformation. Replacing these residues strikingly altered the receptor response to anionic lipids in experiments. High sequence conservation of the same residues among all GPCRs supports a general role for lipid-receptor charge complementarity in signaling.

Global insights into the fine tuning of human A2AAR conformational dynamics in a ternary complex with an engineered G protein viewed by NMR

G protein-coupled receptor (GPCR) conformational plasticity enables formation of ternary signaling complexes with intracellular proteins in response to binding extracellular ligands. We investigate the dynamic process of GPCR complex formation in solution with the human A_2A adenosine receptor (A_2AAR) and an engineered G_s protein, mini-G_s. 2D nuclear magnetic resonance (NMR) data with uniform stable isotope-labeled A_2AAR enabled a global comparison of A_2AAR conformations between complexes with an agonist and mini-G_s and with an agonist alone. The two conformations are similar and show subtle differences at the receptor intracellular surface, supporting a model whereby agonist binding alone is sufficient to populate a conformation resembling the active state. However, an A_2AAR "hot spot" connecting the extracellular ligand-binding pocket to the intracellular surface is observed to be highly dynamic in the ternary complex, suggesting a mechanism for allosteric connection between the bound G protein and the drug-binding pocket involving structural plasticity of the "toggle switch" tryptophan.

Slow conformational dynamics of the human A2A adenosine receptor are temporally ordered

A more complete depiction of protein energy landscapes includes the identification of different function-related conformational states and the determination of the pathways connecting them. We used total internal reflection fluorescence (TIRF) imaging to investigate the conformational dynamics of the human A2A adenosine receptor (A2AAR), a class A G protein-coupled receptor (GPCR), at the single-molecule level. Slow, reversible conformational exchange was observed among three different fluorescence emission states populated for agonist-bound A2AAR. Transitions among these states predominantly occurred in a specific order, and exchange between inactive and active-like conformations proceeded through an intermediate state. Models derived from molecular dynamics simulations with available A2AAR structures rationalized the relative fluorescence emission intensities for the highest and lowest emission states but not the transition state. This suggests that the functionally critical intermediate state required to achieve activation is not currently visualized among available A2AAR structures.

Evaluation of training programme

Resurgence of malaria in the country during seventies and subsequent implementation of Modified Plan of Operation (MPO) through Primary Health Care (PHC) system highlighted the urgent need for short term courses for PHC medical officers and clinicians at the periphery. In pursuance of these objectives. Dte. of National Malaria Eradication Programme (NMEP) laid down series of "Orientation Courses" for medical officers of PHCs and "Workshops" in management of severe and complicated malaria for physicians, paediatricians and pathologists in hospitals/teaching institutions. While there exist standard methods for evaluation of institutional courses, for peripheral short term courses, a new method i.e. "Retrospective assessment at the work sites of the participants" was followed for evaluation of the above mentioned two types of courses. The findings were revealing in as much as, besides being highly successful, medical officers of PHCs who so far did not consider them as part of the programme, then onward aligned themselves as an integral part of the campaign. These courses helped them in updating with knowledge viz. concept of malaria control, passive case detection, dosages and choice of drugs, treatment schedules particularly in pregnancy and significance of quinine and primaquine therapy. Assessment of workshops for clinicians, provided the forum for first ever interaction between clinicians and the programme in the country. The workshops provided an update with current advances/researches in the treatment of severe and complicated cases of malaria. These were considered highly beneficial, as it cleared many doubts about pathological processes and clinical manifestations including induced by drugs. The study also highlighted the deficiencies in the delivery process by the faculty.

Experimental studies of the potentiation of proguanil and pyrimethamine by dapsone using Plasmodium berghei in white mice

An accurate system with stringent criteria has been established to test antimalarial drugs and drug combinations against Plasmodium berghei in mice. Minimum effective doses for a number of antimalarial drugs have been determined when used in this system. Considerable potentiation of the activity of pyrimethamine and to a somewhat less extent of proguanil by dapsone has been demonstrated. The need to extend studies of these combinations to the parasites of human malaria is discussed in terms of establishing a safe chemoprophylactic regime in the presence of drug-resistant strains of parasites.