Specificity of Chaperonin GroEL Binding to the Precursor of the Small Subunit of Ribulose-1,5-Bisphosphate Carboxylase.

Although chaperonin-assisted protein folding has been studied in vitro by a number of investigators, the features of an unfolded or partially folded polypeptide that are recognized and bound by chaperonins are not known. I addressed this question using the precursor of the small subunit (pS) of ribulose-1,5-bisphosphate carboxylase as a model substrate for GroEL, the bacterial chaperonin. The precursor protein was expressed in E. coli as a C-terminal fusion to protein A. Protein A-pS (and any associated cellular proteins) was isolated by affinity chromatography. GroEL could be eluted from the fusion protein by ATP and either GroES or casein, consistent with results of in vitro folding assays. Using deletions from the C-terminus of pS I defined the smallest truncation of pS, PAxpS90T, that binds GroEL with high avidity. A series of site-specific mutations targeting the C-terminal 15-20 amino acids of PAxpS90T was constructed and analyzed for the ability to bind GroEL. Two of these mutations bound significantly less GroEL than PAxpS90T, suggesting that this region is required for avid GroEL binding. I demonstrated a physical interaction between GroEL and this region of pS with a novel assay that utilizes the protection of tyrosine residues from iodination upon formation of specific protein-protein complexes. Finally, I further showed that at least half of the transit sequence of pS is also required for avid binding to GroEL. The association constants for the interaction of GroEL with PAxpS, PAxpS90T, or its mutated derivatives, were determined and fell within the range 3.7\times10\sp7 to 2.7\times 10\sp6 M\sp{-1}. Analysis of the affinity constants for PAxpS90T mutants allowed us to define a possible recognition motif for GroEL\u27s interaction with pS. This motif includes the recognition of both hydrophobic and positively charged amino acids. The motif need not be helical, but structural rigidity may be a requirement for recognition (and binding) by GroEL

Adenylyl cyclases (ACs) (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database

Adenylyl cyclase, E.C. 4.6.1.1, converts ATP to cyclic AMP and pyrophosphate. Mammalian membrane-delimited adenylyl cyclases (nomenclature as approved by the NC-IUPHAR Subcommittee on Adenylyl cyclases [9]) are typically made up of two clusters of six TM domains separating two intracellular, overlapping catalytic domains that are the target for the nonselective activators Gαs (the stimulatory G protein α subunit) and forskolin (except AC9, [21]). adenosine and its derivatives (e.g. 2',5'-dideoxyadenosine), acting through the P-site,are inhibitors of adenylyl cyclase activity [27]. Four families of membranous adenylyl cyclase are distinguishable: calmodulin-stimulated (AC1, AC3 and AC8), Ca2+- and Gβγ-inhibitable (AC5, AC6 and AC9), Gβγ-stimulated and Ca2+-insensitive (AC2, AC4 and AC7), and forskolin-insensitive (AC9) forms. A soluble adenylyl cyclase (AC10) lacks membrane spanning regions and is insensitive to G proteins.It functions as a cytoplasmic bicarbonate (pH-insensitive) sensor [5]

Adenylyl cyclases (ACs) in GtoPdb v.2023.1

Adenylyl cyclase, E.C. 4.6.1.1, converts ATP to cyclic AMP and pyrophosphate. Mammalian membrane-delimited adenylyl cyclases (nomenclature as approved by the NC-IUPHAR Subcommittee on Adenylyl cyclases [11]) are typically made up of two clusters of six TM domains separating two intracellular, overlapping catalytic domains that are the target for the nonselective activators Gαs (the stimulatory G protein α subunit) and forskolin (except AC9, [28]). adenosine and its derivatives (e.g. 2',5'-dideoxyadenosine), acting through the P-site,are inhibitors of adenylyl cyclase activity [35]. Four families of membranous adenylyl cyclase are distinguishable: calmodulin-stimulated (AC1, AC3 and AC8), Ca2+- and Gβγ-inhibitable (AC5, AC6 and AC9), Gβγ-stimulated and Ca2+-insensitive (AC2, AC4 and AC7), and forskolin-insensitive (AC9) forms. A soluble adenylyl cyclase (AC10) lacks membrane spanning regions and is insensitive to G proteins.It functions as a cytoplasmic bicarbonate (pH-insensitive) sensor [7]

Gαi Controls the Gating of the G Protein-Activated K+ Channel, GIRK

AbstractGIRK (Kir3) channels are activated by neurotransmitters coupled to G proteins, via a direct binding of Gβγ. The role of Gα subunits in GIRK gating is elusive. Here we demonstrate that Gαi is not only a donor of Gβγ but also regulates GIRK gating. When overexpressed in Xenopus oocytes, GIRK channels show excessive basal activity and poor activation by agonist or Gβγ. Coexpression of Gαi3 or Gαi1 restores the correct gating parameters. Gαi acts neither as a pure Gβγ scavenger nor as an allosteric cofactor for Gβγ. It inhibits only the basal activity without interfering with Gβγ-induced response. Thus, GIRK is regulated, in distinct ways, by both arms of the G protein. Gαi probably acts in its GDP bound form, alone or as a part of Gαβγ heterotrimer

Dopamine D2 Receptor-Mediated Heterologous Sensitization of AC5 Requires Signalosome Assembly

Chronic dopamine receptor activation is implicated in several central nervous system disorders. Although acute activation of Gαi-coupled D2 dopamine receptors inhibits adenylyl cyclase, persistent activation enhances adenylyl cyclase activity, a phenomenon called heterologous sensitization. Previous work revealed a requirement for Gαs in D2-induced heterologous sensitization of AC5. To elucidate the mechanism of Gαs dependency, we expressed Gαs mutants in Gαs-deficient GnasE2−/E2− cells. Neither Gαs-palmitoylation nor Gαs-Gβγ interactions were required for sensitization of AC5. Moreover, we found that coexpressing βARKct-CD8 or Sar1(H79G) blocked heterologous sensitization. These studies are consistent with a role for Gαs-AC5 interactions in sensitization however, Gβγ appears to have an indirect role in heterologous sensitization of AC5, possibly by promoting proper signalosome assembly

Zinc inhibits TRPV1 to alleviate chemotherapy-induced neuropathic pain

Zinc is a transition metal that has a long history of use as an anti-inflammatory agent. It also soothes pain sensations in a number of animal models. However, the effects and mechanisms of zinc on chemotherapy-induced peripheral neuropathy remain unknown. Here we show that locally injected zinc markedly reduces neuropathic pain in male and female mice induced by paclitaxel, a chemotherapy drug, in a TRPV1-dependent manner. Extracellularly applied zinc also inhibits the function of TRPV1 expressed in HEK293 cells and mouse DRG neurons, which requires the presence of zinc-permeable TRPA1 to mediate entry of zinc into the cytoplasm. Moreover, TRPA1 is required for zinc-induced inhibition of TRPV1-mediated acute nociception. Unexpectedly, zinc transporters, but not TRPA1, are required for zinc-induced inhibition of TRPV1-dependent chronic neuropathic pain produced by paclitaxel. Together, our study demonstrates a novel mechanism underlying the analgesic effect of zinc on paclitaxel-induced neuropathic pain that relies on the function of TRPV1

Physiological Roles of Mammalian Transmembrane Adenylyl Cyclase Isoforms

Adenylyl cyclases (ACs) catalyze the conversion of ATP to the ubiquitous second messenger cAMP. Mammals possess nine isoforms of transmembrane ACs, dubbed AC1-9, that serve as major effector enzymes of G protein-coupled receptors. The transmembrane ACs display varying expression patterns across tissues, giving potential for them having a wide array of physiologic roles. Cells express multiple AC isoforms, implying that ACs have redundant functions. Furthermore, all transmembrane ACs are activated by Gαs so it was long assumed that all ACs are activated by Gαs-coupled GPCRs. AC isoforms partition to different microdomains of the plasma membrane and form prearranged signaling complexes with specific GPCRs that contribute to cAMP signaling compartments. This compartmentation allows for a diversity of cellular and physiological responses by enabling unique signaling events to be triggered by different pools of cAMP. Isoform specific pharmacological activators or inhibitors are lacking for most ACs, making knockdown and overexpression the primary tools for examining the physiological roles of a given isoform. Much progress has been made in understanding the physiological effects mediated through individual transmembrane ACs. GPCR-AC-cAMP signaling pathways play significant roles in regulating functions of every cell and tissue, so understanding each AC isoform\u27s role holds potential for uncovering new approaches for treating a vast array of pathophysiological conditions

G protein-coupled receptor-effector macromolecular membrane assemblies (GEMMAs)

G protein-coupled receptors (GPCRs) are the largest group of receptors involved in cellular signaling across the plasma membrane and a major class of drug targets. The canonical model for GPCR signaling involves three components the GPCR, a heterotrimeric G protein and a proximal plasma membrane effector that have been generally thought to be freely mobile molecules able to interact by 'collision coupling'. Here, we synthesize evidence that supports the existence of GPCR-effector macromolecular membrane assemblies (GEMMAs) comprised of specific GPCRs, G proteins, plasma membrane effector molecules and other associated transmembrane proteins that are pre-assembled prior to receptor activation by agonists, which then leads to subsequent rearrangement of the GEMMA components. The GEMMA concept offers an alternative and complementary model to the canonical collision-coupling model, allowing more efficient interactions between specific signaling components, as well as the integration of the concept of GPCR oligomerization as well as GPCR interactions with orphan receptors, truncated GPCRs and other membrane-localized GPCR-associated proteins. Collision-coupling and pre-assembled mechanisms are not exclusive and likely both operate in the cell, providing a spectrum of signaling modalities which explains the differential properties of a multitude of GPCRs in their different cellular environments. Here, we explore the unique pharmacological characteristics of individual GEMMAs, which could provide new opportunities to therapeutically modulate GPCR signaling