John K. Northup, Ph.D.

Chief
Section on Signal Transduction
Laboratory of Cellular Biology

Research Statement

The Section on Signal Transduction investigates the molecular bases for G-protein signaling with emphasis on sensory signaling processes. In addition to a diverse array of endocrine and neurotransmitter molecules, G-proteins are now known to mediate the signaling events initiating the visual and chemical senses. In the Signal Transduction Section we utilize recombinant expressed proteins and in vitro biochemical and biophysical assays to examine the selectivity and mechanisms of G-protein signaling at the molecular level. For mechanistic studies we have capitalized on the visual signaling models for G-proteins, since retinal sources provide abundant and homogeneous preparations not only of G-proteins but also their coupled receptors (rhodopsins), effectors (cyclic GMP phosphodiesterase and phospholipase C), and all necessary co-factors for efficient signaling. Using the visual proteins we have devised in vitro assay procedures for each known step in G-protein signaling, and we have adapted these procedures to the analysis of G-protein signaling using recombinant expressed receptors and G-protein subunits. Our current research efforts are applying these approaches to the study of the chemical senses examining the molecular bases for taste, smell, and pheromone detection.

Selected Publications

• Ray K, Adepietro K, Chen C, Northup JK. Elucidation of the Role of Peptide Linker in the Ca2+ Receptor Activation Process. J. Biol. Chem. 282, 5310-5317, 2007.
• Sainz E, Gutierrez J, Battey JF, Northup JK, Sullivan SL. Functional characterization of the human T2R7, T2R14, T2R43, and T2R47 bitter receptors (PDF; get Adobe Reader) . Biochem. J. 403, 537-543, 2007.
• Sainz E, Cavenagh MM, LopezJimenez ND, Gutierrez J, Battey JF, Northup JK, Sullivan SL. The G-protein coupling properties of the human T1R taste receptors. J. Neurobiol. 67, 948-959, 2007.
• White JF, Grodnitzky J, Louis, JM, Trinh LB, Shiloach J, Gutierrez J, Northup JK, Grisshammer R. Dimerization of a class A G-protein-coupled receptor alters G-protein activation. Proc. Natl. Acad. Sci USA. 104:12199-12204, 2007.
• Saidak Z, Blake-Palmer K, Hay D, Northup JK, Glass M. Differential Activation of Different G proteins by m-Opioid Receptor Agonists (PDF). Br. J. Pharmacol. 147: 671-680, 2006.
• Engel S, Neumann S, Kaur N, Monga V, Jain R, Northup, JK, Gershengorn MC. Low affinity analogs of thyrotropin-releasing hormone are super-agonists (PDF). J. Biol. Chem. 281: 13103-13109, 2006.
• Ray, Kausik, Tisdale, Justin, Dodd, R.H., Dauban, P., Raut, Martial, and Northup, John K. (2005) Calindol, a Positive Allosteric Modulator of the Human Ca2+ receptor, Activates an Extracellular Ligand-binding Domain-deleted Rhodopsin-like Seven-transmembrane Domain in the Absence of Ca2+. J. Biol. Chem. 280: 37013-37020.
• Ray K, Ghosh SP, Northup JK. The role of cysteines and charged amino acids in extracellular loops of the human Ca(2+) receptor in cell surface expression and receptor activation processes. Endocrinology 145(8):3892–903, 2004.
• Okada M, Northup JK, Ozaki N, Russell JT, Linnoila M, Goldman D. Modification of human 5-HT(2C) receptor function by Cys23Ser, an abundant, naturally occurring amino-acid substitution. Molecular Psychiatry 9(1):55–64, 2004.
• Rebois RV, Schuck P, Northup JK. Elucidating kinetic and thermodynamic constants for interaction of G protein subunits and receptors by surface plasmon resonance spectroscopy. Methods in Enzymology 344:15–42, 2002.
• Jian X, Clark WA, Kowalak J, Markey SP, Simonds WF, Northup JK. Gbetagamma affinity for bovine rhodopsin is determined by the carboxyl-terminal sequences of the gamma subunit. The Journal of Biological Chemistry 276(51):48518–25, 2001.
• Clark WA, Jian X, Chen L, Northup JK. Independent and synergistic interaction of retinal G-protein subunits with bovine rhodopsin measured by surface plasmon resonance. The Biochemical Journal 358(Pt 2):389–97, 2001.
• Kroog GS, Jian X, Chen L, Northup JK, Battey JF. Phosphorylation uncouples the gastrin-releasing peptide receptor from G(q). The Journal of Biological Chemistry 274(51):36700–6, 1999.
• Glass M, Northup JK. Agonist selective regulation of G proteins by cannabinoid CB(1) and CB(2) receptors. Molecular Pharmacology 56(6):1362–9, 1999.
• Donohue PJ, Sainz E, Akeson M, Kroog GS, Mantey SA, Battey JF, Jensen RT, Northup JK. An aspartate residue at the extracellular boundary of TMII and an arginine residue in TMVII of the gastrin-releasing peptide receptor interact to facilitate heterotrimeric G protein coupling. Biochemistry 38(29):9366–72, 1999.
• Jian X, Sainz E, Clark WA, Jensen RT, Battey JF, Northup JK. The Bombesin Receptor Subtypes Have Distinct G Protein Specificities. The Journal of Biological Chemistry 274:11573–11581, 1999.
• Liu W, Clark WA, Sharma P, Northup JK. Mechanism of Allosteric Regulation of the Rod cGMP Phosphodiesterase Activity by the Helical Domain of the Transducin Subunit. The Journal of Biological Chemistry 273:34284–34292, 1998.
• Liu W, Northup JK. The Helical Domain of a G-Protein Subunit is Regulator of its Effector. Proceedings of the National Academy of Sciences of the USA 95:12878–12883, 1998.
• Hellmich MR, Battey JF, Northup JK. Selective reconstitution of gastrin-releasing peptide receptor with G alpha q. Proceedings of the National Academy of Sciences of the USA 94:751–756, 1997.
• Hartman J, Northup JK. Functional reconstitution in situ of 5-hydroxytryptamine2c (5HT2c) receptors with alphaq and inverse agonism of 5HT2c receptor antagonists. The Journal of Biological Chemistry 271:22591–22597, 1996.
• Hoon MA, Northup JK, Margolskee RF, Ryba NJP. Functional expression of the taste specific G-protein, alpha-gustducin. Biochemical Journal 309:629–636, 1995.

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