MicroED structure of the human vasopressin 1B receptor

The small size and flexibility of G protein-coupled receptors (GPCRs) have long posed a significant challenge to determining their structures for research and therapeutic applications. Single particle cryogenic electron microscopy (cryoEM) is often out of reach due to the small size of the receptor without a signaling partner. Crystallization of GPCRs in lipidic cubic phase (LCP) often results in crystals that may be too small and difficult to analyze using X-ray microcrystallography at synchrotron sources or even serial femtosecond crystallography at X-ray free electron lasers. Here, we determine the previously unknown structure of the human vasopressin 1B receptor (V1BR) using microcrystal electron diffraction (MicroED). To achieve this, we grew V1BR microcrystals in LCP and transferred the material directly onto electron microscopy grids. The protein was labeled with a fluorescent dye prior to crystallization to locate the microcrystals using cryogenic fluorescence microscopy, and then the surrounding material was removed using a plasma-focused ion beam to thin the sample to a thickness amenable to MicroED. MicroED data from 14 crystalline lamellae were used to determine the 3.2 Å structure of the receptor in the crystallographic space group P 1. These results demonstrate the use of MicroED to determine previously unknown GPCR structures that, despite significant effort, were not tractable by other methods.

A haplotype of angiotensin receptor type 1 associated with human hypertension increases blood pressure in transgenic mice

The renin-angiotensin system plays an important role in the regulation of blood pressure via angiotensin II and the angiotensin II receptor type 1 (AT1R). Human AT1R gene promoter has four SNPs: T/A at -777, T/G at -680, A/C at -214, and A/G at -119, that are in linkage disequilibrium. Variants -777T, -680T, -214A, and -119A almost always occur together (named haplotype I), and variants -777A, -680G, -214C, and -119G almost always occur together (named haplotype II) in Caucasian subjects. Genomic DNA analyses, from 388 normotensive and 374 hypertensive subjects, link haplotype I of the human AT1R (hAT1R) gene with hypertension in Caucasians (p = 0.004, χ(2) = 8.46). Our results show increased basal promoter activity of the hAT1R gene in cells (H295R and A7r5) transfected with reporter construct containing haplotype I. We also show increased binding of the transcription factor, USF2, to oligonucleotide containing nucleoside -214A as opposed to -214C. Recombineering of a 166-kb bacterial artificial chromosome containing 68 kb of the 5'-flanking region, 45 kb of the coding sequence, and 53 kb of the 3'-flanking region of the hAT1R gene was employed to generate transgenic mice with either haplotype. We show that (a) hAT1R mRNA level is increased in the kidney and heart of transgenic mice containing haplotype I as compared with haplotype II; (b) USF2 binds more strongly to the chromatin obtained from the kidney of transgenic mice containing haplotype I as compared with haplotype II; and (c) blood pressure and oxidative stress are increased in transgenic mice containing haplotype I as compared with haplotype II.

Cross-talk from β-adrenergic receptors modulates α2A-adrenergic receptor endocytosis in sympathetic neurons via protein kinase A and spinophilin

Inter-regulation of adrenergic receptors (ARs) via cross-talk is a long appreciated but mechanistically unclear physiological phenomenon. Evidence from the AR literature and our own extensive studies on regulation of α2AARs by the scaffolding protein spinophilin have illuminated a potential novel mechanism for cross-talk from β to α2ARs. In the present study, we have characterized a mode of endogenous AR cross-talk in native adrenergic neurons whereby canonical βAR-mediated signaling modulates spinophilin-regulated α2AAR endocytosis through PKA. Our findings demonstrate that co-activation of β and α2AARs, either by application of endogenous agonist or by simultaneous stimulation with distinct selective agonists, results in acceleration of endogenous α2AAR endocytosis in native neurons. We show that receptor-independent PKA activation by forskolin is sufficient to accelerate α2AAR endocytosis and that α2AAR stimulation alone drives accelerated endocytosis in spinophilin-null neurons. Endocytic response acceleration by β/α2AAR co-activation is blocked by PKA inhibition and lost in spinophilin-null neurons, consistent with our previous finding that spinophilin is a substrate for phosphorylation by PKA that disrupts its interaction with α2AARs. Importantly, we show that α2AR agonist-mediated α2AAR/spinophilin interaction is blocked by βAR co-activation in a PKA-dependent fashion. We therefore propose a novel mechanism for cross-talk from β to α2ARs, whereby canonical βAR-mediated signaling coupled to PKA activation results in phosphorylation of spinophilin, disrupting its interaction with α2AARs and accelerating α2AAR endocytic responses. This mechanism of cross-talk has significant implications for endogenous adrenergic physiology and for therapeutic targeting of β and α2AARs.