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Lefevre TJ, Wei W, Mukhaleva E, Meda Venkata SP, Chandan NR, Abraham S, Li Y, Dessauer CW, Vaidehi N, Smrcka AV. Stabilization of interdomain interactions in G protein α subunits as a determinant of Gα i subtype signaling specificity. J Biol Chem 2024; 300:107211. [PMID: 38522511 PMCID: PMC11066577 DOI: 10.1016/j.jbc.2024.107211] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2023] [Revised: 03/07/2024] [Accepted: 03/12/2024] [Indexed: 03/26/2024] Open
Abstract
Highly homologous members of the Gαi family, Gαi1-3, have distinct tissue distributions and physiological functions, yet their biochemical and functional properties are very similar. We recently identified PDZ-RhoGEF (PRG) as a novel Gαi1 effector that is poorly activated by Gαi2. In a proteomic proximity labeling screen we observed a strong preference for Gαi1 relative to Gαi2 with respect to engagement of a broad range of potential targets. We investigated the mechanistic basis for this selectivity using PRG as a representative target. Substitution of either the helical domain (HD) from Gαi1 into Gαi2 or substitution of a single amino acid, A230 in Gαi2 with the corresponding D in Gαi1, largely rescues PRG activation and interactions with other potential Gαi targets. Molecular dynamics simulations combined with Bayesian network models revealed that in the GTP bound state, separation at the HD-Ras-like domain (RLD) interface is more pronounced in Gαi2 than Gαi1. Mutation of A230 to D in Gαi2 stabilizes HD-RLD interactions via ionic interactions with R145 in the HD which in turn modify the conformation of Switch III. These data support a model where D229 in Gαi1 interacts with R144 and stabilizes a network of interactions between HD and RLD to promote protein target recognition. The corresponding A230 in Gαi2 is unable to stabilize this network leading to an overall lower efficacy with respect to target interactions. This study reveals distinct mechanistic properties that could underly differential biological and physiological consequences of activation of Gαi1 or Gαi2 by G protein-coupled receptors.
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Affiliation(s)
- Tyler J Lefevre
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan, USA; Program in Chemical Biology, University of Michigan, Ann Arbor, Michigan, USA
| | - Wenyuan Wei
- Department of Computational and Quantitative Medicine, Beckman Research Institute of the City of Hope, Duarte, California, USA
| | - Elizaveta Mukhaleva
- Department of Computational and Quantitative Medicine, Beckman Research Institute of the City of Hope, Duarte, California, USA
| | | | - Naincy R Chandan
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan, USA; Genentech, South San Francisco, California, USA
| | - Saji Abraham
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Yong Li
- Department of Integrative Biology and Pharmacology McGovern Medical School, UTHealth, Houston, Texas, USA
| | - Carmen W Dessauer
- Department of Integrative Biology and Pharmacology McGovern Medical School, UTHealth, Houston, Texas, USA
| | - Nagarajan Vaidehi
- Department of Computational and Quantitative Medicine, Beckman Research Institute of the City of Hope, Duarte, California, USA
| | - Alan V Smrcka
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan, USA.
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2
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Lefevre TJ, Wei W, Mukhaleva E, Venkata SPM, Chandan NR, Abraham S, Li Y, Dessauer CW, Vaidehi N, Smrcka AV. Stabilization of Interdomain Interactions in G protein α i Subunits Determines Gα i Subtype Signaling Specificity. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.10.532072. [PMID: 37066214 PMCID: PMC10103935 DOI: 10.1101/2023.03.10.532072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Highly homologous members of the Gαi family, Gαi1-3, have distinct tissue distributions and physiological functions, yet the functional properties of these proteins with respect to GDP/GTP binding and regulation of adenylate cyclase are very similar. We recently identified PDZ-RhoGEF (PRG) as a novel Gαi1 effector, however, it is poorly activated by Gαi2. Here, in a proteomic proximity labeling screen we observed a strong preference for Gαi1 relative to Gαi2 with respect to engagement of a broad range of potential targets. We investigated the mechanistic basis for this selectivity using PRG as a representative target. Substitution of either the helical domain (HD) from Gαi1 into Gαi2 or substitution of a single amino acid, A230 in Gαi2 to the corresponding D in Gαi1, largely rescues PRG activation and interactions with other Gαi targets. Molecular dynamics simulations combined with Bayesian network models revealed that in the GTP bound state, dynamic separation at the HD-Ras-like domain (RLD) interface is prevalent in Gαi2 relative to Gαi1 and that mutation of A230s4h3.3 to D in Gαi2 stabilizes HD-RLD interactions through formation of an ionic interaction with R145HD.11 in the HD. These interactions in turn modify the conformation of Switch III. These data support a model where D229s4h3.3 in Gαi1 interacts with R144HD.11 stabilizes a network of interactions between HD and RLD to promote protein target recognition. The corresponding A230 in Gαi2 is unable to form the "ionic lock" to stabilize this network leading to an overall lower efficacy with respect to target interactions. This study reveals distinct mechanistic properties that could underly differential biological and physiological consequences of activation of Gαi1 or Gαi2 by GPCRs.
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Affiliation(s)
- Tyler J. Lefevre
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI
- Program in Chemical Biology, University of Michigan, Ann Arbor, MI
| | - Wenyuan Wei
- Department of Integrative Biology and Pharmacology McGovern Medical School, UTHealth, Houston, TX
| | - Elizaveta Mukhaleva
- Department of Integrative Biology and Pharmacology McGovern Medical School, UTHealth, Houston, TX
| | | | - Naincy R. Chandan
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI
- Genentech, South San Francisco, CA
| | - Saji Abraham
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI
| | - Yong Li
- Department of Integrative Biology and Pharmacology McGovern Medical School, UTHealth, Houston, TX
| | - Carmen W. Dessauer
- Department of Integrative Biology and Pharmacology McGovern Medical School, UTHealth, Houston, TX
| | - Nagarajan Vaidehi
- Department of Computational and Quantitative Medicine, Beckman Research Institute of the City of Hope, Duarte, CA
| | - Alan V. Smrcka
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI
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3
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Koval A, Larasati YA, Savitsky M, Solis GP, Good JM, Quinodoz M, Rivolta C, Superti-Furga A, Katanaev VL. In-depth molecular profiling of an intronic GNAO1 mutant as the basis for personalized high-throughput drug screening. MED 2023; 4:311-325.e7. [PMID: 37001522 DOI: 10.1016/j.medj.2023.03.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Revised: 03/01/2023] [Accepted: 03/07/2023] [Indexed: 04/03/2023]
Abstract
BACKGROUND The GNAO1 gene, encoding the major neuronal G protein Gαo, is mutated in a subset of pediatric encephalopathies. Most such mutations consist of missense variants. METHODS In this study, we present a precision medicine workflow combining next-generation sequencing (NGS) diagnostics, molecular etiology analysis, and personalized drug discovery. FINDINGS We describe a patient carrying a de novo intronic mutation (NM_020988.3:c.724-8G>A), leading to epilepsy-negative encephalopathy with motor dysfunction from the second decade. Our data show that this mutation creates a novel splice acceptor site that in turn causes an in-frame insertion of two amino acid residues, Pro-Gln, within the regulatory switch III region of Gαo. This insertion misconfigures the switch III loop and creates novel interactions with the catalytic switch II region, resulting in increased GTP uptake, defective GTP hydrolysis, and aberrant interactions with effector proteins. In contrast, intracellular localization, Gβγ interactions, and G protein-coupled receptor (GPCR) coupling of the Gαo[insPQ] mutant protein remain unchanged. CONCLUSIONS This in-depth analysis characterizes the heterozygous c.724-8G>A mutation as partially dominant negative, providing clues to the molecular etiology of this specific pathology. Further, this analysis allows us to establish and validate a high-throughput screening platform aiming at identifying molecules that could correct the aberrant biochemical functions of the mutant Gαo. FUNDING This work was supported by the Joint Seed Money Funding scheme between the University of Geneva and the Hebrew University of Jerusalem.
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Affiliation(s)
- Alexey Koval
- Translational Research Center in Oncohaematology, Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, 1211 Geneva, Switzerland
| | - Yonika A Larasati
- Translational Research Center in Oncohaematology, Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, 1211 Geneva, Switzerland
| | - Mikhail Savitsky
- Translational Research Center in Oncohaematology, Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, 1211 Geneva, Switzerland
| | - Gonzalo P Solis
- Translational Research Center in Oncohaematology, Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, 1211 Geneva, Switzerland
| | - Jean-Marc Good
- Division of Genetic Medicine, Lausanne University Hospital (CHUV), 1011 Lausanne, Switzerland
| | - Mathieu Quinodoz
- Institute of Molecular and Clinical Ophthalmology Basel (IOB), 4031 Basel, Switzerland; Department of Ophthalmology, University of Basel, 4031 Basel, Switzerland; Department of Genetics and Genome Biology, University of Leicester, Leicester LE1 7RH, UK
| | - Carlo Rivolta
- Institute of Molecular and Clinical Ophthalmology Basel (IOB), 4031 Basel, Switzerland; Department of Ophthalmology, University of Basel, 4031 Basel, Switzerland; Department of Genetics and Genome Biology, University of Leicester, Leicester LE1 7RH, UK
| | - Andrea Superti-Furga
- Division of Genetic Medicine, Lausanne University Hospital (CHUV), 1011 Lausanne, Switzerland
| | - Vladimir L Katanaev
- Translational Research Center in Oncohaematology, Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, 1211 Geneva, Switzerland; Institute of Life Sciences and Biomedicine, Far Eastern Federal University, 690090 Vladivostok, Russia.
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4
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Cleator JH, Wells CA, Dingus J, Kurtz DT, Hildebrandt JD. The N54- αs Mutant Has Decreased Affinity for βγ and Suggests a Mechanism for Coupling Heterotrimeric G Protein Nucleotide Exchange with Subunit Dissociation. J Pharmacol Exp Ther 2018; 365:219-225. [PMID: 29491039 DOI: 10.1124/jpet.117.245779] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Accepted: 02/23/2018] [Indexed: 11/22/2022] Open
Abstract
Ser54 of Gsα binds guanine nucleotide and Mg2+ as part of a conserved sequence motif in GTP binding proteins. Mutating the homologous residue in small and heterotrimeric G proteins generates dominant-negative proteins, but by protein-specific mechanisms. For αi/o, this results from persistent binding of α to βγ, whereas for small GTP binding proteins and αs this results from persistent binding to guanine nucleotide exchange factor or receptor. This work examined the role of βγ interactions in mediating the properties of the Ser54-like mutants of Gα subunits. Unexpectedly, WT-αs or N54-αs coexpressed with α1B-adrenergic receptor in human embryonic kidney 293 cells decreased receptor stimulation of IP3 production by a cAMP-independent mechanism, but WT-αs was more effective than the mutant. One explanation for this result would be that αs, like Ser47 αi/o, blocks receptor activation by sequestering βγ; implying that N54-αS has reduced affinity for βγ since it was less effective at blocking IP3 production. This possibility was more directly supported by the observation that WT-αs was more effective than the mutant in inhibiting βγ activation of phospholipase Cβ2. Further, in vitro synthesized N54-αs bound biotinylated-βγ with lower apparent affinity than did WT-αs The Cys54 mutation also decreased βγ binding but less effectively than N54-αs Substitution of the conserved Ser in αo with Cys or Asn increased βγ binding, with the Cys mutant being more effective. This suggests that Ser54 of αs is involved in coupling changes in nucleotide binding with altered subunit interactions, and has important implications for how receptors activate G proteins.
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Affiliation(s)
- John H Cleator
- Department of Pharmacology, Medical University of South Carolina, Charleston, South Carolina
| | - Christopher A Wells
- Department of Pharmacology, Medical University of South Carolina, Charleston, South Carolina
| | - Jane Dingus
- Department of Pharmacology, Medical University of South Carolina, Charleston, South Carolina
| | - David T Kurtz
- Department of Pharmacology, Medical University of South Carolina, Charleston, South Carolina
| | - John D Hildebrandt
- Department of Pharmacology, Medical University of South Carolina, Charleston, South Carolina
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5
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Duc NM, Kim HR, Chung KY. Structural mechanism of G protein activation by G protein-coupled receptor. Eur J Pharmacol 2015; 763:214-22. [PMID: 25981300 DOI: 10.1016/j.ejphar.2015.05.016] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2015] [Revised: 03/03/2015] [Accepted: 05/11/2015] [Indexed: 12/17/2022]
Abstract
G protein-coupled receptors (GPCRs) are a family of membrane receptors that regulate physiology and pathology of various organs. Consequently, about 40% of drugs in the market targets GPCRs. Heterotrimeric G proteins are composed of α, β, and γ subunits, and act as the key downstream signaling molecules of GPCRs. The structural mechanism of G protein activation by GPCRs has been of a great interest, and a number of biochemical and biophysical studies have been performed since the late 80's. These studies investigated the interface between GPCR and G proteins and the structural mechanism of GPCR-induced G protein activation. Recently, arrestins are also reported to be important molecular switches in GPCR-mediated signal transduction, and the physiological output of arrestin-mediated signal transduction is different from that of G protein-mediated signal transduction. Understanding the structural mechanism of the activation of G proteins and arrestins would provide fundamental information for the downstream signaling-selective GPCR-targeting drug development. This review will discuss the structural mechanism of GPCR-induced G protein activation by comparing previous biochemical and biophysical studies.
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Affiliation(s)
- Nguyen Minh Duc
- School of Pharmacy, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon 440-746, Republic of Korea
| | - Hee Ryung Kim
- School of Pharmacy, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon 440-746, Republic of Korea
| | - Ka Young Chung
- School of Pharmacy, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon 440-746, Republic of Korea.
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6
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Leyme A, Marivin A, Casler J, Nguyen LT, Garcia-Marcos M. Different biochemical properties explain why two equivalent Gα subunit mutants cause unrelated diseases. J Biol Chem 2014; 289:21818-27. [PMID: 24982418 DOI: 10.1074/jbc.m114.549790] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
There is an increasing number of disease-associated Gα mutations identified from genome-wide sequencing campaigns or targeted efforts. Albright's Hereditary Osteodystrophy (AHO) was the first inherited disease associated with loss-of-function mutations in a G protein (Gαs) and other studies revealed gain-of-function Gα mutations in cancer. Here we attempted to solve the apparent quandary posed by the fact that the same mutation in two different G proteins appeared associated with both AHO and cancer. We first confirmed the presence of an inherited Gαs-R265H mutation from a previously described clinical case report of AHO. This mutation is structurally analogous to Gαo-R243H, an oncogenic mutant with increased activity in vitro and in cells due to rapid nucleotide exchange. We found that, contrary to Gαo-R243H, Gαs-R265H activity is compromised due to greatly impaired nucleotide binding in vitro and in cells. We obtained equivalent results when comparing another AHO mutation in Gαs (D173N) with a counterpart cancer mutation in Gαo (D151N). Gαo-R243H binds nucleotides efficiently under steady-state conditions but releases GDP much faster than the WT protein, suggesting diminished affinity for the nucleotide. These results indicate that the same disease-linked mutation in two different G proteins affects a common biochemical feature (nucleotide affinity) but to a different grade depending on the G protein (mild decrease for Gαo and severe for Gαs). We conclude that Gαs-R265H has dramatically impaired nucleotide affinity leading to the loss-of-function in AHO whereas Gαo-R243H has a mild decrease in nucleotide affinity that causes rapid nucleotide turnover and subsequent hyperactivity in cancer.
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Affiliation(s)
- Anthony Leyme
- From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118
| | - Arthur Marivin
- From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118
| | - Jason Casler
- From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118
| | - Lien T Nguyen
- From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118
| | - Mikel Garcia-Marcos
- From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118
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7
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Garcia-Marcos M, Ghosh P, Farquhar MG. Molecular basis of a novel oncogenic mutation in GNAO1. Oncogene 2011; 30:2691-6. [PMID: 21317923 DOI: 10.1038/onc.2010.645] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Heterotrimeric G proteins are molecular switches that control signal transduction, and their dysregulation can promote oncogenesis. Somatic mutations in GNAS, GNAI2 and GNAQ genes induce oncogenesis by rendering Gα subunits constitutively activated. Recently the first somatic mutation, arginine(243) → histidine (R243H) in the GNAO1 (Gαo) gene was identified in breast carcinomas and shown to promote oncogenic transformation when introduced into cells. Here, we provide the molecular basis for the oncogenic properties of the Gαo R243H mutant. Using limited proteolysis assays, nucleotide-binding assays, and single-turnover and steady-state GTPase assays, we demonstrate that the oncogenic R234H mutation renders Gαo constitutively active by accelerating the rate of nucleotide exchange; however, this mutation does not affect Gαo's ability to become deactivated by GTPase-activating proteins (GAPs) or by its intrinsic GTPase activity. This mechanism differs from that of previously reported oncogenic mutations that impair GTPase activity and GAP sensitivity without affecting nucleotide exchange. The constitutively active Gαo R243H mutant also enhances Src-STAT3 signaling in NIH-3T3 cells, a pathway previously shown to be directly triggered by active Gαo proteins to promote cellular transformation. Based on structural analyses, we propose that the enhanced rate of nucleotide exchange in Gαo R243H results from loss of the highly conserved electrostatic interaction of R243 with E43, located in the in the P-loop that represents the binding site for the α- and β-phosphates of the nucleotide. We conclude that the novel R234H mutation imparts oncogenic properties to Gαo by accelerating nucleotide exchange and rendering it constitutively active, thereby enhancing signaling pathways, for example, src-STAT3, responsible for neoplastic transformation.
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Affiliation(s)
- M Garcia-Marcos
- Department of Cellular and Molecular Medicine, San Diego School of Medicine, University of California, La Jolla, CA 92093-0651, USA.
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8
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Ramachandran S, Cerione RA. A dominant-negative Galpha mutant that traps a stable rhodopsin-Galpha-GTP-betagamma complex. J Biol Chem 2011; 286:12702-11. [PMID: 21285355 DOI: 10.1074/jbc.m110.166538] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Residues comprising the guanine nucleotide-binding sites of the α subunits of heterotrimeric (large) G-proteins (Gα subunits), as well as the Ras-related (small) G-proteins, are highly conserved. This is especially the case for the phosphate-binding loop (P-loop) where both Gα subunits and Ras-related G-proteins have a conserved serine or threonine residue. Substitutions for this residue in Ras and related (small) G-proteins yield nucleotide-depleted, dominant-negative mutants. Here we have examined the consequences of changing the conserved serine residue in the P-loop to asparagine, within a chimeric Gα subunit (designated αT*) that is mainly comprised of the α subunit of the retinal G-protein transducin and a limited region from the α subunit of Gi1. The αT*(S43N) mutant exhibits a significantly higher rate of intrinsic GDP-GTP exchange compared with wild-type αT*, with light-activated rhodopsin (R*) causing only a moderate increase in the kinetics of nucleotide exchange on αT*(S43N). The αT*(S43N) mutant, when bound to either GDP or GTP, was able to significantly slow the rate of R*-catalyzed GDP-GTP exchange on wild-type αT*. Thus, GTP-bound αT*(S43N), as well as the GDP-bound mutant, is capable of forming a stable complex with R*. αT*(S43N) activated the cGMP phosphodiesterase (PDE) with a dose-response similar to wild-type αT*. Activation of the PDE by αT*(S43N) was unaffected if either R* or β1γ1 alone was present, whereas it was inhibited when R* and the β1γ1 subunit were added together. Overall, our studies suggest that the S43N substitution on αT* stabilizes an intermediate on the G-protein activation pathway consisting of an activated G-protein-coupled receptor, a GTP-bound Gα subunit, and the β1γ1 complex.
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Affiliation(s)
- Sekar Ramachandran
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-6401, USA
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9
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Obligatory role in GTP hydrolysis for the amide carbonyl oxygen of the Mg(2+)-coordinating Thr of regulatory GTPases. Proc Natl Acad Sci U S A 2010; 107:9596-601. [PMID: 20457940 DOI: 10.1073/pnas.1004803107] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
When G-protein alpha subunits binds GTP and Mg(2+), they transition from their inactive to their active conformation. This transition is accompanied by completion of the coordination shell of Mg(2+) with electrons from six oxygens: two water molecules, the ss and gamma phosphoryls of GTP, a helix-alpha1 Ser, and a switch I domain (SWI) Thr, and the repositioning of SWI and SWII domains. SWII binds and regulates effector enzymes and facilitates GTP hydrolysis by repositioning the gamma-carbonyl of a Gln. Mutating the Ser generates regulatory GTPases that cannot lock Mg(2+) into its place and are locked in their inactive state with dominant negative properties. Curiously, mutating the Thr appears to reduce GTP hydrolysis. The reason for this difference is not known because it is also not known why removal of the Thr should affect the overall GTPase cycle differently than removal of the Ser. Working with recombinant Gsalpha, we report that mutating its SWI-Thr to either Ala, Glu, Gln, or Asp results not only in diminished GTPase activity but also in spontaneous activation of the SWII domain. Upon close examination of existing alpha subunit crystals, we noted the oxygen of the backbone carbonyl of SWI-Thr and of the gamma-carbonyl of SWII Gln to be roughly equidistant from the oxygen of the hydrolytic H(2)O. Our observations indicate that the Gln and Thr carbonyls play equihierarchical roles in the GTPase process and provide the mechanism that explains why mutating the Thr mimics mutating the Gln and not that of the Ser.
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10
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Johnston CA, Willard FS, Ramer JK, Blaesius R, Roques CN, Siderovski DP. State-selective binding peptides for heterotrimeric G-protein subunits: novel tools for investigating G-protein signaling dynamics. Comb Chem High Throughput Screen 2009; 11:370-81. [PMID: 18537558 DOI: 10.2174/138620708784534798] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Heterotrimeric G-proteins, comprising Galpha, Gbeta, and Ggamma subunits, are molecular switches that regulate numerous signaling pathways involved in cellular physiology. This characteristic is achieved by the adoption of two principal states: an inactive state in which GDP-bound Galpha is complexed with the Gbetagamma dimer, and an active state in which GTP-bound Galpha is freed of its Gbetagamma binding partner. Structural studies have illustrated the basis for the distinct conformations of these states which are regulated by alterations in three precise 'switch regions' of the Galpha subunit. Discrete differences in conformation between GDP- and GTP-bound Galpha underlie its nucleotide-dependent protein-protein interactions (e.g., with Gbetagamma/receptor and effectors, respectively) that are critical for maintaining their proper nucleotide cycling and signaling properties. Recently, several screening approaches have been used to identify peptide sequences capable of interacting with Galpha (and free Gbetagamma) in nucleotide-dependent fashions. These peptides have demonstrated applications in direct modulation of the nucleotide cycle, assessing the structural basis for aspects of Galpha and Gbetagamma signaling, and serving as biosensor tools in assays for Galpha activation including high throughput drug screening. In this review, we highlight some of the methods used for such discoveries and discuss the insights that can be gleaned from application of these identified peptides.
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Affiliation(s)
- Christopher A Johnston
- Department of Pharmacology, Lineberger Comprehensive Cancer Center, and UNC Neuroscience Center, School of Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7365, USA
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11
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Abstract
Heterotrimeric G proteins couple the activation of heptahelical receptors at the cell surface to the intracellular signaling cascades that mediate the physiological responses to extracellular stimuli. G proteins are molecular switches that are activated by receptor-catalyzed GTP for GDP exchange on the G protein alpha subunit, which is the rate-limiting step in the activation of all downstream signaling. Despite the important biological role of the receptor-G protein interaction, relatively little is known about the structure of the complex and how it leads to nucleotide exchange. This chapter will describe what is known about receptor and G protein structure and outline a strategy for assembling the current data into improved models for the receptor-G protein complex that will hopefully answer the question as to how receptors flip the G protein switch.
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Affiliation(s)
- William M Oldham
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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12
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Johnston CA, Afshar K, Snyder JT, Tall GG, Gönczy P, Siderovski DP, Willard FS. Structural determinants underlying the temperature-sensitive nature of a Galpha mutant in asymmetric cell division of Caenorhabditis elegans. J Biol Chem 2008; 283:21550-8. [PMID: 18519563 DOI: 10.1074/jbc.m803023200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Heterotrimeric G-proteins are integral to a conserved regulatory module that influences metazoan asymmetric cell division (ACD). In the Caenorhabditis elegans zygote, GOA-1 (Galpha(o)) and GPA-16 (Galpha(i)) are involved in generating forces that pull on astral microtubules and position the spindle asymmetrically. GPA-16 function has been analyzed in vivo owing notably to a temperature-sensitive allele gpa-16(it143), which, at the restrictive temperature, results in spindle orientation defects in early embryos. Here we identify the structural basis of gpa-16(it143), which encodes a point mutation (G202D) in the switch II region of GPA-16. Using Galpha(i1)(G202D) as a model in biochemical analyses, we demonstrate that high temperature induces instability of the mutant Galpha. At the permissive temperature, the mutant Galpha was stable upon GTP binding, but switch II rearrangement was compromised, as were activation state-selective interactions with regulators involved in ACD, including GoLoco motifs, RGS proteins, and RIC-8. We solved the crystal structure of the mutant Galpha bound to GDP, which indicates a unique switch II conformation as well as steric constraints that suggest activated GPA-16(it143) is destabilized relative to wild type. Spindle severing in gpa-16(it143) embryos revealed that pulling forces are symmetric and markedly diminished at the restrictive temperature. Interestingly, pulling forces are asymmetric and generally similar in magnitude to wild type at the permissive temperature despite defects in the structure of GPA-16(it143). These normal pulling forces in gpa-16(it143) embryos at the permissive temperature were attributable to GOA-1 function, underscoring a complex interplay of Galpha subunit function in ACD.
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Affiliation(s)
- Christopher A Johnston
- Department of Pharmacology and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599, USA
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13
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The same mutation in Gsalpha and transducin alpha reveals behavioral differences between these highly homologous G protein alpha-subunits. Proc Natl Acad Sci U S A 2008; 105:2363-8. [PMID: 18258741 DOI: 10.1073/pnas.0712261105] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mutating Arg-238 to Glu (R238E) in the switch 3 region of a transducin alpha (*Talpha) in which 27 aa of the GTPase domain have been replaced with those of the alpha-subunit of the inhibitory G protein 1 (Gi1alpha), was reported to create an alpha-subunit that is resistant to activation by GTPgammaS, is devoid of resident nucleotide, and has dominant negative (DN) properties. In an attempt to create a DN stimultory G protein alpha (Gsalpha) with a single mutation we created Gsalpha-R265E, equivalent to *Talpha-R238E. Gsalpha-R265E has facilitated activation by GTPgammaS, a slightly facilitated activation by GTP but much reduced receptor plus GTP stimulated activation, and an apparently unaltered ability to interact with receptor as seen in ligand binding studies. Further, the activity profile of Gsalpha-R265E is that of an alpha-subunit with unaltered or increased GTPase activity. The only change in Gsalpha that is similar to that in *Talpha is that the apparent affinity for guanine nucleotides is decreased in both proteins. The molecular basis of the changed properties are discussed based on the known crystal structure of Gsalpha and the changes introduced by the same mutation in a *Talpha (Gtalpha*) with only 23 aa from Gi1alpha. Gtalpha*-R238E, with four fewer mutations in switch 3, was reported to show no evidence of DN properties, is activated by GTPgammaS, and has reduced GTPase activity. The data highlight a critical role for the switch 3 region in setting overall properties of signal-transducing GTPases.
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14
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Heterotrimeric G protein activation by G-protein-coupled receptors. Nat Rev Mol Cell Biol 2008; 9:60-71. [PMID: 18043707 DOI: 10.1038/nrm2299] [Citation(s) in RCA: 798] [Impact Index Per Article: 49.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Heterotrimeric G proteins have a crucial role as molecular switches in signal transduction pathways mediated by G-protein-coupled receptors. Extracellular stimuli activate these receptors, which then catalyse GTP-GDP exchange on the G protein alpha-subunit. The complex series of interactions and conformational changes that connect agonist binding to G protein activation raise various interesting questions about the structure, biomechanics, kinetics and specificity of signal transduction across the plasma membrane.
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15
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Abstract
G-protein-coupled receptors (GPCRs) represent the largest class of membrane proteins and are the targets of 25-50% of drugs currently on the market. Dominant negative mutant Galpha subunits of heterotrimeric G-proteins have been extensively utilized to delineate G-protein signaling pathways and represent a promising new tool to study GPCR-dependent signaling in the CNS. There are different regions in various types of Galpha subunits in which mutations can give rise to a dominant negative phenotype. Such a mutant Galpha would compete with wild-type Galpha for binding to other proteins involved in the G-protein cycle and either block or reduce the response caused by wild-type Galpha. To date, there are three different mechanisms described for dominant negative Galpha subunits: sequestration of the Gbetagamma subunits, sequestration of the activated GPCR by the heterotrimeric complex, and sequestration of the activated GPCR by nucleotide-free Galpha. This review focuses on the development of dominant negative Galpha subunits, the different mechanisms used by various mutant Galpha subunits, and potential structural changes underlying the dominant negative effects.
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Affiliation(s)
- Brandy Barren
- Department of Molecular Physiology and Biophysics, University of Iowa College of Medicine, 51 Newton Road, Iowa City, IA 52242, USA
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16
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Johnston CA, Lobanova ES, Shavkunov AS, Low J, Ramer JK, Blaesius R, Fredericks Z, Willard FS, Kuhlman B, Arshavsky VY, Siderovski DP. Minimal determinants for binding activated G alpha from the structure of a G alpha(i1)-peptide dimer. Biochemistry 2006; 45:11390-400. [PMID: 16981699 PMCID: PMC2597383 DOI: 10.1021/bi0613832] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
G-proteins cycle between an inactive GDP-bound state and an active GTP-bound state, serving as molecular switches that coordinate cellular signaling. We recently used phage display to identify a series of peptides that bind G alpha subunits in a nucleotide-dependent manner [Johnston, C. A., Willard, F. S., Jezyk, M. R., Fredericks, Z., Bodor, E. T., Jones, M. B., Blaesius, R., Watts, V. J., Harden, T. K., Sondek, J., Ramer, J. K., and Siderovski, D. P. (2005) Structure 13, 1069-1080]. Here we describe the structural features and functions of KB-1753, a peptide that binds selectively to GDP x AlF4(-)- and GTPgammaS-bound states of G alpha(i) subunits. KB-1753 blocks interaction of G alpha(transducin) with its effector, cGMP phosphodiesterase, and inhibits transducin-mediated activation of cGMP degradation. Additionally, KB-1753 interferes with RGS protein binding and resultant GAP activity. A fluorescent KB-1753 variant was found to act as a sensor for activated G alpha in vitro. The crystal structure of KB-1753 bound to G alpha(i1) x GDP x AlF4(-) reveals binding to a conserved hydrophobic groove between switch II and alpha3 helices and, along with supporting biochemical data and previous structural analyses, supports the notion that this is the site of effector interactions for G alpha(i) subunits.
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Affiliation(s)
- Christopher A. Johnston
- Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7365
| | - Ekaterina S. Lobanova
- Department of Ophthalmology and Neurobiology, Duke University, Durham, North Carolina 27710
| | - Alexander S. Shavkunov
- Department of Ophthalmology and Neurobiology, Duke University, Durham, North Carolina 27710
| | - Justin Low
- Department of Biochemistry & Biophysics, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7365
| | - J. Kevin Ramer
- Department of Karo Bio USA, Durham, North Carolina 27703
| | | | | | - Francis S. Willard
- Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7365
| | - Brian Kuhlman
- Department of Biochemistry & Biophysics, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7365
| | - Vadim Y. Arshavsky
- Department of Ophthalmology and Neurobiology, Duke University, Durham, North Carolina 27710
| | - David P. Siderovski
- Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7365
- To whom correspondence should be addressed: UNC Pharmacology, 1106 M.E. Jones Bldg., Chapel Hill, NC 27599-7365. Telephone: 919-843-9363. Fax: 919-966-5640. E-mail:
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17
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Geiser AH, Sievert MK, Guo LW, Grant JE, Krebs MP, Fotiadis D, Engel A, Ruoho AE. Bacteriorhodopsin chimeras containing the third cytoplasmic loop of bovine rhodopsin activate transducin for GTP/GDP exchange. Protein Sci 2006; 15:1679-90. [PMID: 16815918 PMCID: PMC2265101 DOI: 10.1110/ps.062192306] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The mechanisms by which G-protein-coupled receptors (GPCRs) activate G-proteins are not well understood due to the lack of atomic structures of GPCRs in an active form or in GPCR/G-protein complexes. For study of GPCR/G-protein interactions, we have generated a series of chimeras by replacing the third cytoplasmic loop of a scaffold protein bacteriorhodopsin (bR) with various lengths of cytoplasmic loop 3 of bovine rhodopsin (Rh), and one such chimera containing loop 3 of the human beta2-adrenergic receptor. The chimeras expressed in the archaeon Halobacterium salinarum formed purple membrane lattices thus facilitating robust protein purification. Retinal was correctly incorporated into the chimeras, as determined by spectrophotometry. A 2D crystal (lattice) was evidenced by circular dichroism analysis, and proper organization of homotrimers formed by the bR/Rh loop 3 chimera Rh3C was clearly illustrated by atomic force microscopy. Most interestingly, Rh3C (and Rh3G to a lesser extent) was functional in activation of GTPgamma35S/GDP exchange of the transducin alpha subunit (Galphat) at a level 3.5-fold higher than the basal exchange. This activation was inhibited by GDP and by a high-affinity peptide analog of the Galphat C terminus, indicating specificity in the exchange reaction. Furthermore, a specific physical interaction between the chimera Rh3C loop 3 and the Galphat C terminus was demonstrated by cocentrifugation of transducin with Rh3C. This Galphat-activating bR/Rh chimera is highly likely to be a useful tool for studying GPCR/G-protein interactions.
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Affiliation(s)
- Andrew H Geiser
- Department of Pharmacology, University of Wisconsin Medical School, Madison 53706, USA
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18
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Herrmann R, Heck M, Henklein P, Hofmann KP, Ernst OP. Signal Transfer from GPCRs to G Proteins. J Biol Chem 2006; 281:30234-41. [PMID: 16847064 DOI: 10.1074/jbc.m600797200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Catalysis of nucleotide exchange in heterotrimeric G proteins (Galphabetagamma) is a key step in cellular signal transduction mediated by G protein-coupled receptors. The Galpha N terminus with its helical stretch is thought to be crucial for G protein/activated receptor (R(*)) interaction. The N-terminal fatty acylation of Galpha is important for membrane targeting of G proteins. By applying biophysical techniques to the rhodopsin/transducin model system, we studied the effect of N-terminal truncations in Galpha. In Galphabetagamma, lack of the fatty acid and Galpha truncations up to 33 amino acids had little effect on R(*) binding and R(*)-catalyzed nucleotide exchange, implying that this region is not mandatory for R(*)/Galphabetagamma interaction. However, when the other hydrophobic modification of Galphabetagamma, the Ggamma C-terminal farnesyl moiety, is lacking, R(*) interaction requires the fatty acylated Galpha N terminus. This suggests that the two hydrophobic extensions can replace each other in the interaction of Galphabetagamma with R(*). We propose that in native Galphabetagamma, these two terminal regions are functionally redundant and form a microdomain that serves both to anchor the G protein to the membrane and to establish an initial docking complex with R(*). Accordingly, we find that the native fatty acylated Galpha is competent to interact with R(*) even in the absence of Gbetagamma, whereas nonacylated Galpha requires Gbetagamma for interaction. Experiments with N-terminally truncated Galpha subunits suggest that in the second step of the catalytic process, the receptor binds to the alphaN/beta1-loop region of Galpha to reduce nucleotide affinity and to make the Galpha C terminus available for subsequent interaction with R(*).
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Affiliation(s)
- Rolf Herrmann
- Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, Schumannstrasse 20/21, D-10098 Berlin, Germany
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19
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Oldham WM, Van Eps N, Preininger AM, Hubbell WL, Hamm HE. Mechanism of the receptor-catalyzed activation of heterotrimeric G proteins. Nat Struct Mol Biol 2006; 13:772-7. [PMID: 16892066 DOI: 10.1038/nsmb1129] [Citation(s) in RCA: 145] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2006] [Accepted: 07/06/2006] [Indexed: 12/31/2022]
Abstract
Heptahelical receptors activate intracellular signaling pathways by catalyzing GTP for GDP exchange on the heterotrimeric G protein alpha subunit (G alpha). Despite the crucial role of this process in cell signaling, little is known about the mechanism of G protein activation. Here we explore the structural basis for receptor-mediated GDP release using electron paramagnetic resonance spectroscopy. Binding to the activated receptor (R*) causes an apparent rigid-body movement of the alpha5 helix of G alpha that would perturb GDP binding at the beta6-alpha5 loop. This movement was not observed when a flexible loop was inserted between the alpha5 helix and the R*-binding C terminus, which uncouples R* binding from nucleotide exchange, suggesting that this movement is necessary for GDP release. These data provide the first direct observation of R*-mediated conformational changes in G proteins and define the structural basis for GDP release from G alpha.
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Affiliation(s)
- William M Oldham
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6600, USA
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20
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Guo LW, Assadi-Porter FM, Grant JE, Wu H, Markley JL, Ruoho AE. One-step purification of bacterially expressed recombinant transducin alpha-subunit and isotopically labeled PDE6 gamma-subunit for NMR analysis. Protein Expr Purif 2006; 51:187-97. [PMID: 16938469 DOI: 10.1016/j.pep.2006.07.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2006] [Revised: 06/22/2006] [Accepted: 07/03/2006] [Indexed: 11/23/2022]
Abstract
Interactions between the transducin alpha-subunit (Galpha(t)) and the cGMP phosphodiesterase gamma-subunit (PDEgamma) are critical not only for turn-on but also turn-off of vertebrate visual signal transduction. Elucidation of the signaling mechanisms dominated by these interactions has been restrained by the lack of atomic structures for full-length Galpha(t)/PDEgamma complexes, in particular, the signaling-state complex represented by Galpha(t).GTPgammaS/PDEgamma. As a preliminary step in our effort for NMR structural analysis of Galpha(t)/PDEgamma interactions, we have developed efficient protocols for the large-scale production of recombinant Galpha(t) (rGalpha(t)) and homogeneous and functional isotopically labeled PDEgamma from Escherichia coli cells. One-step purification of rGalpha(t) was achieved through cobalt affinity chromatography in the presence of glycerol, which effectively removed the molecular chaperone DnaK that otherwise persistently co-purified with rGalpha(t). The purified rGalpha(t) was found to be functional in GTPgammaS/GDP exchange upon activation of rhodopsin and was used to form a signaling-state complex with labeled PDEgamma, rGalpha(t). GTPgammaS/[U-13C,15N]PDEgamma. The labeled PDEgamma sample yielded a well-resolved 1H-15N HSQC spectrum. The methods described here for large-scale production of homogeneous and functional rGalpha(t) and isotope-labeled PDEgamma should support further NMR structural analysis of the rGalpha(t)/PDEgamma complexes. In addition, our protocol for removing the co-purifying DnaK contaminant may be of general utility in purifying E. coli-expressed recombinant proteins.
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Affiliation(s)
- Lian-Wang Guo
- Department of Pharmacology, University of Wisconsin, Madison, WI 53706, USA.
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21
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Natochin M, Barren B, Artemyev NO. Dominant negative mutants of transducin-alpha that block activated receptor. Biochemistry 2006; 45:6488-94. [PMID: 16700559 PMCID: PMC2525804 DOI: 10.1021/bi060381e] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Mutations counterpart to dominant negative RasSer17Asn in the alpha-subunits of heterotrimeric G-proteins are known to also produce dominant negative effects. The mechanism of these mutations remains poorly understood. Here, we examined the effects and mechanism of the Ser43Cys and Ser43Asn mutants of transducin-like chimeric Gtalpha* in the visual signaling system. Our analysis showed that both mutants have reduced affinity for GDP and are likely to exist in an empty-or partially occupied-pocket state. S43C and S43N retained the ability to interact with Gtbetagamma and, as heterotrimeric proteins, bind to photoexcited rhodopsin (R*). The interaction with R* is unproductive as the mutants failed to bind GTPgammaS and become activated. S43C and S43N inhibited R*-dependent activation of Gtalpha* and Gtalpha, apparently by blocking R*. Finally, both Gtalpha* mutants lacked interaction with the gamma-subunit of PDE6, an effector protein in phototransduction. These results indicate that the S43C and S43N mutants of Gtalpha* are dominant negative inhibitors that bind and block the activated receptor in a mechanism that parallels that of RasSer17Asn. Dominant negative mutants of Gtalpha sequestering R*, such as S43C and S43N, may become useful instruments in probing the mechanisms of visual dysfunctions caused by abnormal phototransduction signaling.
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Affiliation(s)
- Michael Natochin
- Department of Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA
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