David Naranjo

Estructura y Función de Sensores Moleculares

Profesor Titular

Doctor en Ciencias mención Biología (1991)

Universidad de Chile

Curriculum Vitae

Contact information:

E-mail david.naranjo at uv.cl
Teléfono: (56)-(32)-2508024, Fax: (56)-(32)-2508027
Dirección: Centro de Neurociencias de Valparaíso.
Facultad de Ciencias, Universidad de Valparaíso.
Gran Bretaña 1111. Playa Ancha. Valparaíso. Chile.

Research Statement:

Voltage gated K+ channels determine the threshold of excitation and shape the action potential and its duration in neurons and other excitable tissues. The core of our research has been focused on functional and structural aspects of these membrane proteins, their voltage dependence, their permeation properties, and how these two processes mutually crosstalk. We use genetic engineering techniques together with patch clamp and voltage clamp recording, and molecular dynamics to address this issue.

We have developed a rich arsenal of mutant K+ channels and an array of questions about their specific role in the physiology of organisms. What makes a K+ channel conductance to be high or low? Why? What is the importance of having a tight or loose electromechanical coupling in some channels? Are there specific physiological requirements for such high voltage sensitivity of K+ channels? How their specific design is determined by their location in the neuron where they are? On what part of the neuron we should look for K+ channels having a given repertoire of biophysical properties?

Voltage gated potassium channels have force us to use biologically dirty words as maximization, optimization etc.  We have found that voltage sensitivity is extremely high in Shaker K+ channels, a channel originally found in the Drosophila fly. Such voltage dependence has evolved as an adaptive tuning of neuronal excitability or is it a physical chemical maximization in the number of charged resides allowed to be in the membrane without disrupting its structure? We have proposed that such voltage dependence is so high that any charge addition (positive or negative) to its voltage sensor has been found to reduce it, as if voltage dependence was maximized in these channels (Gonzalez-Perez et al., 2010).  On the other hand, we have found that, albeit having a selectivity filter apparently optimized for selective and efficient K+ ion conduction,  Shaker K+ channel unitary conductance suffered evolutionary pressure to retain its conductance small by keeping the internal entrance of its pore to be very narrow,  just enough to host a hydrated K+ (Díaz-Franulic et al., 2015a).  

We have learned in detail the structural and functional impact of numerous mutations. However, we envision the need to assess their physiological impact by reinserting genetically modified channels in animals with a suitable genetic background.  Such maneuver could provide useful information to design gene therapy strategies because Shaker is a protein we know so well that we can tune its function with great precision; thus, we could predict the physiological impact of a given genetically engineered K+ channel.  Today, we are inserting functionally engineered Shaker K+ channels back into Drosophila to test for their mechanism of assemble in vivo. For more details, I am more than happy to talk largely on this subject.  

(This picture will be removed shortly)

 

Collaborations:

We have close collaboration with the other members of the molecular sensors group and with Dr. Gonzalez-Nilo with whom we test with Molecular Dynamics simulations the functional impact of the structural modifications introduced into the K+ channels. We are also extensively collaborating  with John Ewer´s lab.

Selected Publications:

  • Naranjo D, Brehm P. (1993). Modal shifts in acetylcholine receptor channel gating confer subunit-dependent desensitization. Science. 260:1811-1814.
  • Naranjo D, Plant C, Dunlap K, Brehm P. (1994). Two subcellular mechanisms underlie calcium-dependent facilitation of bioluminescence. Neuron. 13:1293-1301.
  • NaranjoD, Miller C. (1996). A strongly interacting pair of residues on the contact surface of charybdotoxin and a Shaker K-channel. Neuron. 16:123-130
  • Scanlon M, Naranjo D, Thomas L, Alewood P, Lewis R, Craik D. (1997). Solution structure and proposed binding mechanism of a novel potassium channel toxin kappa-conotoxin PVIIA. Structure. 5:1585-1597.
  • García E, Scanlon M, Naranjo D. (1999). A marine snail toxin shares with scorpion toxins a convergent mechanism of blockade on the pore of voltage-gated K channels. Journal of General Physiology. 114:141-157.
  • Saldaña C, Naranjo D, Coria R, Peña A, Vaca L. (2002). Splitting the two pore domains from TOK1 results in two cationic channels with novel functional properties. Journal of Biological Chemistry. 277:4797-7805. 
  • Naranjo D. (2002). Inhibition of Single Shaker K Channels by kappa-Conotoxin-PVIIA. Biophysical Journal. 82:3003-3011.
  • Oliva C, González V, Naranjo D. (2005). Slow inactivation in voltage gated potassium channels is insensitive to the binding of pore occluding peptide toxins. Biophysical Journal. 89:1009-1019.
  • Gonzalez-Gutierrez G, Miranda-Laferte E, Naranjo D, Hidalgo P, Neely A. (2008) Mutations of nonconserved residues within the calcium channel alpha1-interaction domain inhibit beta-subunit potentiation. Journal of General Physiology. 132(3):383-395.
  • González-Pérez V, Neely A, Tapia C, González-Gutiérrez G, Contreras G, Orio P, Lagos V, Rojas G, Estévez T, Stack K, Naranjo D. (2008) Slow inactivation in Shaker K channels is delayed by intracellular tetraethylammonium. Journal of General Physiology. 132(6):633-650.
  • González-Pérez V, Stack K, Boric K, Naranjo D. (2010) Reduced voltage sensitivity in a K+-channel voltage sensor by electric field remodeling. Proc Natl Acad Sci U S A. 107:5178-5183.
  • Moscoso C. , A. Vergara-Jaque, V. Márquez-Miranda, R. V. Sepúlveda, I. Valencia, I. Díaz-Franulic, F. González-Nilo and D. Naranjo. (2012)  K+ conduction and Mg2+ blockade in an unusually high conductance Kv channel single point mutant. Biophysical  Journal. 103:1198-1207.
  • Naranjo D, Wen H, Brehm P. (2015)  Zebrafish CaV2.1 calcium channels are tailored for fast synchronous neuromuscular transmission.  Biophysical  Journal. 108:578-584.
  • Díaz-Franulic, I., R. Sepúlveda, N. Navarro-Quezada, F. González-Nilo and D. Naranjo. (2015)  Pore dimensions and the role of occupancy in unitary conductance of Shaker K-channels. The Journal of General Physiology. 146:133-146,.
  • Moldenhauer, H., Díaz-Franulic, I., González-Nilo F., Naranjo, D.  (2015)  Effective pore size and radius of capture for K+ ions in K-channels. Scentific Reports. Submitted.