Cynthia Czajkowski

The opening and closing of ligand-gated ion channels (LGICs), which lie in the membranes of nerve cells, regulate information flow throughout the brain. Members of the pentameric LGIC superfamily include nicotinic acetylcholine receptors (nAChR), serotonin-type-3 receptors, gamma-aminobutyric acid type A receptors (GABAR) and glycine receptors. Defects in these channels lead to a variety of neurological diseases and psychiatric disorders. A number of therapeutic drugs, including muscle relaxants, sedative-hypnotics, anti-convulsants, anxiolytics, intravenous and volatile anesthetics, anti-emetics, drugs for nicotine addiction and drugs to treat Alzheimer’s disease target these channels. For these receptors, binding of neurotransmitter in the extracellular ligand-binding domain triggers opening of an intrinsic ion channel more than 50A away in the transmembrane domain of the receptor. Although we know a fair amount about the structure of these receptors, the mechanisms by which the binding of neurotransmitter triggers channel opening and the binding of drugs modulate pLGIC function are relatively unknown.

The major focus of the lab is on understanding the function and structure of the GABAR. GABARs mediate the majority of inhibition in the brain and are modulated by a variety of clinically important drugs, such as benzodiazepines, barbiturates, neurosteroids, anesthetics and anti-convulsants. Furthermore, GABAR mutations have been linked to familial epilepsies, schizophrenia and autism.

Work in my lab is focused on understanding how GABARs and related pLGICs work. First, how does GABA binding trigger the opening of the chloride-selective pore? Second, how does the binding of different drugs such as benzodiazepines, anesthetics, neurosteroids and barbiturates modulate GABAAR function? Third, how do GABAAR defects alter receptor function and contribute to disease? Finally, how do neurons control the assembly, trafficking and cell surface expression of GABAARs? We are using an array of biochemical, biophysical and electrophysiological approaches including two-electrode voltage clamping and patch-clamping, voltage clamp fluorimetry, rapid-ligand application, disulfide trapping, cysteine cross-linking, structural modeling, protein over-expression and purification, and SDSL-EPR to advance our understanding of how neurotransmitter binding is linked to pLGIC activation and how drug binding is coupled to receptor modulation.

Our work is providing new insights into how neurotransmitters activate pLGICs and how allosteric drugs modulate their activity. A deeper understanding of how these channels work at a molecular level will improve our ability to predict the actions of drugs and ligands that act on these channels, design safer and more effective drugs, develop better therapeutic strategies, and understand the etiology of disease-causing mutations.

Figure 1 (above left): GABAAR homology model of extracellular NH2 domain. Subunit interfaces involved in forming the GABA and benzodiazepine (BZD) binding sites are labeled. (top view from synaptic side)	Figure 2 (above right): GABA binding site subunit interface. Binding site “Loops” C and F are labeled. Receptor activation may involve movements (red arrows) of these loops.

Selected Publications

• Venkatachalan SP and CZAJKOWSKI, C. (in press) A structural link between the GABA receptor’s agonist binding site and inner b-sheet governs channel activation and allosteric drug modulation. J. Biol. Chem. published January 4, 2012 doi:10.1074/jbc.M111.316836
• Morlock, E. V. and CZAJKOWSKI, C. (2011) Different residues in the GABA-A receptor benzodiazepine binding pocket mediate benzodiazepine efficacy and binding. Mol. Pharmacol. 80: 14-22 PMCID: PMC3127544 [Available on 2012/7/1]
• Dellisanti, C.D., Hanson, S.M., Chen, L. and CZAJKOWSKI, C. (2011) Packing of the extracellular domain hydrophobic core has evolved to facilitate pentameric ligand-gated ion channel function. J. Biol. Chem. 286: 3658-3670. PMCID: PMC3030369 [Available on 2012/2/4]
• Sancar, F. and CZAJKOWSKI, C. (2011) Allosteric modulators induce distinct movements at the GABA-binding site interface of the GABA-A receptor. Neuropharmacology 60:520-528. PMCID: PMC3026633 [Available on 2012/2/1]
• Hanson, S.M. and CZAJKOWSKI, C. (2011) Disulfide trapping of the GABA-A receptor reveals the importance of the coupling interface in benzodiazepine action. British J. Pharmacol. 162:673-687. Accepted manuscript online: 13 OCT 2010 07:46AM EST | DOI: 10.1111/j.1476-5381.2010.01073.x PMC Journal – In Process
• Wagoner, K.R. and CZAJKOWSKI, C. (2010) Stoichiometry of Expressed a4b2d g-aminobuytric acid type A receptors depends on the ratio of subunit unit cDNA transfected. J. Biol. Chem. 285: 14187-14194 PMCID: PMC2863200 [Available on 2011/5/7]
• Boileau, A.J., Pearce, R. A. and CZAJKOWSKI, C. (2010) The short splice variant of the g2 subunit acts as an external modulator of GABAA receptor function. J. Neurosci. 30: 4895-4903 PMCID: PMC2891256
• Muroi, Y., Theusch, C.M., CZAJKOWSKI, C., and Jackson, M.B. (2009) Distinct structural changes in the GABA-A receptor elicited by pentobarbital and GABA. Biophysical Journal. 96: 499-509. PMCID: PMC2716461 (Paper was one of five highlighted papers for the January 21st issue. Paper received a Faculty of 1000 Medicine citation.).
• Hanson, S.M., Morlock, E.V., Satyshur, K.A., and CZAJKOWSKI, C. (2008) Structural requirements for eszopiclone and zolpidem binding to the GABA_A receptor are different. J. Med. Chem. 51: 7243-7252. PMCID: PMC2645942 [Available on 2009/11/27]
• Venkatachalan, S. and CZAJKOWSKI, C. (2008) A conserved salt-bridge critical for GABAA receptor function and loop C dynamics. Proc. Natl. Acad. Sci. 105: 13604-13609. PMCID: PMC2533236
• Sharkey LM. and Czajkowski C. (2008) Individually monitoring ligand-induced changes in the structure of the GABAA receptor at benzodiazepine binding site and non-binding-site interfaces. Mol Pharmacol. 2008 Jul;74(1):203-12. Epub 2008 Apr 18.
  PDF
• Mercado J. and Czajkowski C. (2008) Gamma-aminobutyric acid (GABA) and pentobarbital induce different conformational rearrangements in the GABA A receptor alpha1 and beta2 pre-M1 regions. J Biol Chem. May 30;283(22):15250-7. Epub 2008 Apr 3.
  PDF
• Hanson SM, Czajkowski C. (2008) Structural mechanisms underlying benzodiazepine modulation of the GABA(A) receptor. J Neurosci. 2008 Mar 26;28(13):3490-9.
  PDF
• Sancar, F., Ericksen, S.S., Kucken, A.M., Teissere, J.A. and Czajkowski, C. (2007) Structural determinants for high affinity zolpidem binding to GABA-A receptors. Mol. Pharmacol 71: 38-46. Epub 2006 Sep 29.
  PDF
• Kloda, J. H. and Czajkowski, C. (2007) Agonist-, antagonist-, and benzodiazepine-induced structural changes in the a1Met113-Leu132 region of the GABA-A receptor. Mol. Pharmacol 71: 483-493. Epub 2006 Nov 15.
  PDF
• Muroi Y, Czajkowski C, Jackson MB. (2006) Local and Global Ligand-Induced Changes in the Structure of the GABA(A) ReceptorBiochemistry Jun 13;45(23):7013-22. PMID: 16752892 [PubMed – in process]
  PDF
• Mercado J, Czajkowski C. (2006) Charged residues in the alpha1 and beta2 pre-M1 regions involved in GABAA receptor activation J Neurosci. Feb 15;26(7):2031-40. PMID: 16481436 [PubMed – indexed for MEDLINE]
  PDF
• Boileau AJ, Pearce RA, Czajkowski C. (2005) Tandem subunits effectively constrain GABAA receptor stoichiometry and recapitulate receptor kinetics but are insensitive to GABAA receptor-associated protein. J Neurosci. Dec 7;25(49):11219-30. PMID: 16339017 [PubMed – indexed for MEDLINE]
  PDF
• Czajkowski C. (2005) Neurobiology: triggers for channel opening Nature. Nov 10;438(7065):167-8. No abstract available. PMID: 16281019 [PubMed – indexed for MEDLINE]
  PDF
• Wagner, D.A., Czajkowski, C., and Jones, M.V. (2004) An arginine involved in GABA binding and unbinding but not gating of the GABA-A receptor J. Neurosci. 24: 2733-2741.
  PDF
• Sancar, F. and Czajkowski, C. (2004) A GABA-A receptor mutation linked to human epilepsy (g2 R43Q) impairs cell surface expression of abg receptors. J. Biol. Chem. 279: 47034-47039.
  PDF
• Newell, J. G., McDevitt, and Czajkowski, C. (2004) Mutation of glutamate 155 of the GABA-A receptor b2 subunit produces a spontaneously open channel: A trigger for channel activation. J. Neurosci. 24: 11226-11235.
  PDF