Lymphocyte Electrophysiology / György Panyi

Personal data: 

György Panyi
M.D., Ph.D., D.Sc.
E-mail: panyi[at]med.unideb.hu

http://www.biophys.dote.hu/elphys

Research: 

Background:
Ion channels expressed in T lymphocytes play key roles in the control of the membrane potential and calcium signaling. The membrane potential- and Ca2+-dependent signal transduction pathways are critical during the activation of these cells upon antigenic stimulation. The voltage-gated Kv1.3 K+ channels are primarily responsible for the regulation of membrane potential in resting and effector memory T cells. Interference with the physiological activity of the Kv1.3 channels attenuate or prevent the response of T-cells to antigenic challenge resulting in immune suppression. The activity of Kv1.3 channels can be influenced primarily by three mechanisms: by high affinity blockers, by influencing the biophysical properties of the channels or by altering the membrane microenvironment/interacting partners/postsythetic modification of the channels. Research in the laboratory focuses on these three major mechanisms.

1. Molecular pharmacology of T-cell ion channels.
Small peptides (30-35 amino acids), isolated from scorpion venoms, are very potent inhibitors of K+ channels (~nM, pM affinities). Since block of Kv1.3 channels inhibits T cell activation and proliferation, these blockers could serve as templates for the development of high affinity and high specificity K+ channel inhibitor drugs for the treatment of several autoimmune diseases mediated by effector memory T cells. In the past we have identified one of the highest affinity Kv1.3 inhibitors, Pi2, from the scorpion Pandinus imperator (Kd= 44 pM). We also identified the first Kv1.3 blocker (Tc32) lacking the essential diad of critically positioned amino acids previously claimed to be required for K+ channel recognition. Recently, we have isolated and pharmacologically characterized a variety of peptide toxins blocking Kv1.3 channels with nanomolar affinity, including Anuroctoxin; Ce1, Ce2 and Ce4; Css20; and Tst26.
Current research in this field aims at increasing the affinity and specificity of the toxins for Kv1.3 channels. This includes the solid-phase or recombinant production of the toxins and introduction of mutations at positions where affinity and specificity changes are anticipated based on sequence alignment of the toxins and computer modeling of the toxin-channel interactions (Figure 1).

2, Biophysics of voltage-gated potassium channels.
Inactivation of voltage-gated potassium channels limits the K+ conductance available for the membrane-potential control of the cells. Using biophysical and molecular biological methods our laboratory identified the molecular mechanism being responsible for the effects of the extracellular acidification on the inactivation kinetics of Kv1.3 channels. We showed that protonation of His399 in the channel pore creates an energy barrier for K+ ions to leave the pore thereby slowing the inactivation kinetics. The gates and gating transitions of voltage –gated K+ channels have been well characterized in isolation but whether the gates are kinetically or energetically coupled is unknown (Figure 2). We have determined recently that the rate of activation gate movement depends on the state of the inactivation gate. Because activation and slow inactivation are ubiquitous gating processes in potassium channels, the cross talk between them is likely to be a fundamental factor in controlling ion flux across membranes. We also determined that the conformation of the aqueous cavity between the activation and inactivation gate is different in open and inactivated channels, and thus the cavity contributes to the coupling between the gates.
Current research in this field aims at identifying the molecular mechanism of coupling between activation and inactivation gates of voltage-gated K+ channels, and delineating of gating transitions leading to recovery from inactivation.

3, Distribution of Kv1.3 channels in the lymphocyte membrane.
Recruitment of membrane proteins into a signaling platform referred to as immunological synapse (IS) is the key step in the activation of T lymphocytes. We have shown earlier that lateral distribution of Kv1.3 K+ channel cells in the T cell membrane is not random, and the channel co-localizes with the T cell receptor/CD3 complex. Moreover, Kv1.3 is recruited into the immunological synapse formed between cytotoxic T cells and target cells.
Current research in this field aims at identifying the physiological consequences of the recruitment of Kv1.3 channels into the immunological synapse. This includes the characterization of post-synthetic modification of the channels by kinases and phosphatases recruited into the IS and the analysis of membrane potential regulation of cells depending on the distribution of the K+ channels in the membrane.

 

Photos: 

 

 

Figure 1: Css20 toxin (yellow) docked on the external vestibule of the Kv1.3 channel. Residues of the channels making direct interaction with the toxin are colored as follows: acidic (Asp and Glu), red; basic (Arg, His and Lys), blue; polar (Asn, Gln, Ser and Thr), cyan; hydrophobic (Gly, Met, Pro and Val), green and; aromatic (Tyr), orange.

 

 

 

 

 

 

 

 

Figure 2: Structure of the pore region (residues 322-450) of Kv1.2. Two subunits are shown as ribbon representations and residues homologous to Shaker 449 (blue) and 474 (yellow) are depicted as spacefilling atoms. K+ ions are shown as green spheres.

 

 

 

 

 

Publications: 

Representative publications:

1. Panyi G, Deutsch C: Crosstalk Between Activation and Slow Inactivation Gates of Shaker Potassium Channels. J.Gen.Physiol, 2006, 128, 547-559., IF:4.831

2. Somodi S, Varga Z, Hajdu P, Starkus JG, Levy DI, Gaspar R, Panyi G: pH dependent modulation of Kv1.3 inactivation: the role of His399. Am.J Physiol Cell Physiol, 2004, 287, C1067-C1076., IF: 4.23

3. Panyi G, Vamosi G, Bodnar A, Gaspar RJ, Damjanovich S: Looking through ion channels: recharged concepts in T cell signaling. Trends Immunol., 2004, 25, 565-569., IF: 9.48

4. Hajdu P, Varga Z, Pieri C, Panyi G, Gaspar R, Jr.: Cholesterol modifies the gating of Kv1.3 in human T lymphocytes. Pflugers Arch., 2003, 445, 674-682., IF:3.842

5. Peter MJ, Varga Z, Hajdu P, Gaspar RJ, Damjanovich S, Horjales E, Possani LD, Panyi G: Effects of toxins Pi2 and Pi3 on human T lymphocyte Kv1.3 channels: the role of Glu7 and Lys24. J Membr.Biol, 2001, 179, 13-25., IF: 2.527

Recent publications:

1. Corzo G, Papp F, Varga Z, Barraza O, Espino-Solis PG, Rodriguez de la Vega RC, Gaspar R, Panyi G, Possani LD: A selective blocker of Kv1.2 and Kv1.3 potassium channels from the venom of the scorpion Centruroides suffusus suffusus. Biochem.Pharmacol., 2008, 76, 1142-1154., IF:4.006

2. Panyi G, Deutsch C. Probing the cavity of the slow inactivated conformation of shaker potassium channels. J.Gen.Physiol, 2007, 129, 403-418., IF:4.831

3. Panyi G, Possani LD, Rodriguez de la Vega RC, Gaspar R, Varga Z: K+ channel blockers: novel tools to inhibit T cell activation leading to specific immunosuppression. Curr.Pharm.Des, 2006, 12, 2199-2220., IF:4.868

4. Bagdany M, Batista CV, Valdez-Cruz NA, Somodi S, Rodriguez de la Vega RC, Licea AF, Varga Z, Gaspar R, Possani LD, Panyi G: Anuroctoxin, a new scorpion toxin of the alpha-KTx 6 subfamily, is highly selective for Kv1.3 over IKCa1 ion channels of human T lymphocytes. Mol.Pharmacol., 2005, 67, 1034-1044., IF:4.088

5. Panyi G, Vamosi G, Bacso Z, Bagdany M, Bodnar A, Varga Z, Gaspar R, Matyus L, Damjanovich S: Kv1.3 potassium channels are localized in the immunological synapse formed between cytotoxic and target cells. Proc.Natl.Acad.Sci.U.S.A, 2004, 101, 1285-1290., IF:9.598