Profesor Titular

Doctor en Ciencias mención Biología (1991)

Universidad de 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.

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.