William Catterall, Ph.D.
Professor
Pharmacology, University of Washington

Electrical impulses generated by nerve, skeletal muscle, and heart muscle cells play an essential role in coordination of most physiological functions and in information processing, learning and memory in the central nervous system. Electrical signals are transmitted from cell to cell by synaptic transmission. Research in this laboratory is focused on the voltage-gated sodium and calcium channels which are responsible for action potential generation in nerve and muscle and for initiation of synaptic transmission. We study the structure and function of these ion channels, their regulation by physiological pathways, drugs, and neurotoxins, and their role in coordination of electrical excitability and synaptic transmission in neurons.

Purified channel proteins, cloned DNA probes which encode the structure of these ion channels, site-directed mutagenesis and functional expression, and site-directed antibodies which recognize specific peptide segments are used to probe the molecular mechanisms of ion channel function, biosynthesis, assembly, and localization. The sodium channel beta subunits have been found to serve as both modulators of channel activity and cell adhesion molecules which may determine channel localization. Specific protein segments of the pore-forming alpha subunits which form the voltage sensors and inactivation gate of the sodium channel have been defined and their functional roles determined by mutagenesis and biophysical analysis. The three-dimensional structure of the inactivation gate of the sodium channel has been determined by NMR methods and correlated with its physiological function.

Regulation of ion channel properties by physiological stimuli is of great interest as a potential mechanism of information processing, learning, and memory in the central nervous system. Sites of phosphorylation by specific protein kinases and sites of binding of G protein subunits which modulate sodium and calcium channel function have been identified. A novel A Kinase Anchoring Protein which targets cAMP-dependent protein kinase to sodium and calcium channels has been discovered and characterized at the molecular and functional levels. In addition, a synaptic protein interaction (synprint) site through which presynaptic calcium channels interact with the SNARE proteins involved in transmitter release has been identified and shown to play a critical role in synaptic transmission and in calcium channel regulation.

Clinically important drugs, including local anesthetics, antiarrhythmics, antiepileptics, and calcium antagonists alter the properties of voltage-sensitive ion channels. We are currently investigating the sites and mechanisms by which these drugs alter the properties of ion channels in order to define the mechanism of drug action at the molecular level and identify common themes which may be important in development of new therapeutic agents. Recent work has led to the identification of the receptor sites for the calcium antagonist drugs on calcium channels and the receptor sites for local anesthetic drugs and multiple neurotoxins on sodium channels.

http://depts.washington.edu/phcol/faculty/catterall.php

William Guggino, Ph.D.
Professor
Physiology, Johns Hopkins University

Current research interests include ion channels, gene therapy, polycystic kidney disease, epithelial cell biology, protein trafficking and localization, and cystic fibrosis. Presently, investigating the structure and function of Cl- and water channels; trafficking and molecular organization of transport proteins in epithelial cell membranes; and genetic therapies for the correction of defective ion transport in CF cells and patients. Research is also being conducted on the identification of the specific defect in Cl- channel regulation in patients with Cystic Fibrosis, the most common autosomal recessive disease in North America.

http://www.guggino.org/

Richard Huganir, Ph.D.
Professor
Neuroscience, Johns Hopkins University

Our laboratory is interested in the mechanisms that regulate synaptic transmission and synaptic plasticity. The general approach we have taken is to study molecular and cellular mechanisms that regulate neurotransmitter receptors. These receptors mediate the response of neurons to neurotransmitters released at synapses and are a central convergence point for transmission of signals between neurons. Modulation of the function of these receptors is a powerful and efficient way to modulate synaptic communication and synaptic plasticity. Over the years we have shown that receptor protein phosphorylation and the regulation of the synaptic targeting of receptors are dynamically regulated and regulate the efficiency of synaptic transmission. We are currently focusing our efforts on the mechanisms that underlie the regulation of the glutamate receptors, the major excitatory neurotransmitter receptors in the brain. These receptors are neurotransmitter-dependent ion channels that allow ions to pass through the neuronal cell membrane, resulting in the excitation of neuronal activity.

http://www.bs.jhmi.edu/neuroscience/huganir/index.htm

Craig Montell, Ph.D.
Professor
Biological Chemistry, Johns Hopkins University

The TRP superfamily of cation channels is comprised of 28 mammalian members as well as 13 Drosophila proteins, all of which are permeable to cations, contain six transmembrane segments and exhibit varying degrees of sequence homology. However, TRP channels are remarkable in their diversity of biological functions, cation selectivities and activation mechanisms. Nevertheless, a recurring theme is that TRP channels play important roles in sensory physiology.

We identified the first member of the TRP superfamily as part of our characterization of Drosophila visual transduction. We found that TRP associates with a supramolecular signaling complex, the signalplex, which includes many of the proteins required for visual transduction. However, some proteins, such as the rhodopsin regulatory protein, arrestin, which do not bind directly to the signalplex, undergo rapid light dependent shuttling in the photoreceptor cells. We showed that the dynamic movements of arrestin functions in adaptation and is mediated by phosphoinositide-dependent interactions with the NINAC myosin III.

Most recently, our laboratory has identified and characterized the roles of several additional Drosophila TRP channels that function in other sensory modalities. Finally, we have initiated a new project to exploit Drosophila as a model to study the relationship of TRP channels and neurodegenerative disease.

http://biolchem.bs.jhmi.edu/members/facultydetail.asp?PersonID=674

Rajini Rao, Ph.D.
Professor
Physiology, Johns Hopkins University

The Rao laboratory uses yeast as a model organism to study novel ion transporters in the endomembranes of cells. Much of our work focuses on the secretory pathway Ca2+/Mn2+-ATPase and the endosomal Na+/H+ exchanger. Both were first discovered in yeast and shown to be founding members of new gene families that are ubiquitously distributed in eukaryotes. Our studies have uncovered fundamental mechanisms in salt tolerance, calcium signaling, manganese detoxification, pH control and vesicle trafficking that are common to yeast, plants and animals. More recently, we have extended our studies to mammalian systems where they have relevance to human health and disease. Future directions of our research will see the increasing use of high throughput phenotype screening and genome-wide approaches to analyze structure-function correlates in ion transporters, and to uncover the functions of novel genes in ion homeostasis, antifungal drug sensitivity and cell signaling pathways. For information on specific projects and references, please visit our website

http://www.bs.jhmi.edu/physiology/raolab/home.html

Solomon Snyder M.D., D.Sc., Ph.D. (Hon. Causa)
Professor
Neuroscience, Johns Hopkins University

Our lab studies diverse signaling systems including those of neurotransmitters and second messengers as well as the actions of drugs upon these processes. We have been interested in atypical neurotransmitters such as nitric oxide (NO), carbon monoxide (CO), and the D-isomers of certain amino acids, specifically D-serine and D-aspartate. A particular focus has been upon downstream targets of NO. Besides its stimulation of cGMP formation, NO acts by nitrosylating a wide range of target proteins including prominent intracellular proteins such as the sodium pump and tubulin. Recently we showed that nitrosylation mediates a novel interaction between the two major small molecule inflammatory systems in cells, NO formed by inducible NO synthase (iNOS) and the prostaglandin-forming COX2 enzyme. iNOS and COX2 bind physiologically with NO formed by iNOS nitrosylating and activating COX2. Inhibitors of iNOS-COX2 binding block prostaglandin formation which may afford a novel means of develoing anti-inflammatory drugs.

We have discovered and characterized a novel cell death signaling cascade whereby cell stressors activate iNOS or neuronal NOS with the generated NO nitrosylating the glycolytic enzyme glyceraldehyde-3-phosphate-dehydrogenase (GAPDH). Nitrosylation terminates the catalytic activity of the enzyme and confers upon it the ability to bind to Siah, a ubiquitin-3-ligase, which mediates nuclear translocation of GAPDH. In the nucleus GAPDH initiates cell death apparently by binding to the protein acetylating enzyme p300 and activating it to stimulate p53, a tumor suppressor that kills cells. This signaling cascade extends from the outside of the cell to the nucleus in a few simple steps, participates in diverse modes of cell death and provides multiple sites for intervention by drugs to prevent cell death and be potentially therapeutic in conditions such as stroke and neurodegenerative disease. We showed that Deprenyl, a drug used to treat Parkinson’s disease and which protects neurons from cell death, acts by blocking the nitrosylation of GAPDH and its binding to Siah. Moreover, the ability of huntingtin, the protein mutated in Huntington’s Disease, to enter the nucleus and kill neurons stems from its binding to GAPDH and Siah.

We have established that D-serine is a novel neurotransmitter which acts by stimulating the “glycine” site of glutamate-NMDA receptors. D-serine is formed primarily in glia which are activated by glutamate leading to the stimulation of serine racemase, the enzyme which converts L- to D-serine with release of D-serine.

In past years we identified, isolated and elucidated receptors for the second messenger IP3, which releases intracellular calcium. We have been studying higher inositol phosphates, especially IP7 which contains an energetic pyrophosphate bond. We discovered that IP7 phosphorylates proteins in a fashion rather different than does ATP. This phosphorylation is a non-enzymatic auto-phosphorylation. Most remarkably, the phosphate from IP7 is added only to sites on proteins that are already phosphorylated, hence IP7 pyrophosphorylates protein targets, a novel form of protein phosphorylation and a unique means of signal transduction. Studies involving deletion of IP6 kinase, the enzyme that forms IP7 by phosphorylating IP6, reveal physiologic roles for IP7 in the trafficking of synaptic and other types of vesicles, apoptosis, chemotaxis, and telomere elongation. One of the three IP6 kinase enzymes, IP6 kinase 2, appears to be physiologically associated with cell death induction. It is normally bound in the cytoplasm to the heat shock protein HSP90 which maintains it in an inactive form. Anti-cancer drugs that block this binding lead to increased IP7 formation in cell death.

http://neuroscience.jhu.edu/SolomonSnyder.php

back to top