World Library  
Flag as Inappropriate
Email this Article

Halorhodopsins

Article Id: WHEBN0005999582
Reproduction Date:

Title: Halorhodopsins  
Author: World Heritage Encyclopedia
Language: English
Subject: Behavioral neuroscience
Collection:
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Halorhodopsins

Halorhodopsin is a light-gated ion channel, specific for chloride ions, and found in phylogenetically ancient archaea, known as halobacteria. It is a seven-transmembrane protein of the retinylidene protein family, homologous to the light-driven proton pump bacteriorhodopsin, and similar in tertiary structure (but not primary sequence structure) to vertebrate rhodopsins, the pigments that sense light in the retina. Halorhodopsin also shares sequence similarity to channelrhodopsin, another light-driven ion channel. Halorhodopsin contains the essential light-isomerizable vitamin A derivative all-trans-retinal. Due to the intense attention on solving the structure and function of this molecule, halorhodopsin is one of the few membrane proteins whose crystal structure is known.

Halorhodopsin uses the energy of green/yellow light to move chloride ions into the cell, overcoming the membrane potential. Beside chlorides it transports other halides and nitrates into the cell. Potassium chloride uptake by cells helps to maintain osmotic balance during cell growth. By performing the same task, light-driven anion pumps can considerably reduce the use of metabolic energy. Halorhodopsin has been the subject of much study and its structure is accurately known. Its properties are similar to those of bacteriorhodopsin, and these two light-driven ion pumps transport cations and anions in opposite directions.

Halorhodopsin isoforms can be found in multiple species of halobacteria, including H. salinarum, and N. pharaonis. Much ongoing research is exploring these differences, and using them to parse apart the photocycle and pump properties. After bacteriorhodopsin, halorhodopsin may be the best type I (microbial) opsin studied. Peak absorbance of the halorhodopsin retinal complex is about 570 nm.

Just as the blue-light activated ion channel channelrhodopsin-2 opens up the ability to activate excitable cells (such as neurons, muscle cells, pancreatic cells, and immune cells) with brief pulses of blue light, halorhodopsin opens up the ability to silence excitable cells with brief pulses of yellow light. Thus halorhodopsin and channelrhodopsin together enable multiple-color optical activation, silencing, and desynchronization of neural activity, creating a powerful neuroengineering toolbox.[1] [2]

Halorhodopsin from Natronomonas (NpHR) has been used achieve inhibition of action potentials in neurons in mammalian systems. Since light activation of NpHR leads to an influx of chloride ions which is a part of the natural process for generating hyperpolarization, NpHR induced inhibition works very well in neurons. Original NpHR channels when expressed in mammalian cells, showed a tendency to get accumulated in the Endoplasmic reticulum of the cells.[3] To overcome the sub-cellular localization issues, an ER export motif was added to the NpHR sequence. This modified NpHR (celled eNpHR2.0) was utilized successfully to drive aggregate-free, high level expression of NpHR in vivo.[4] However, even the modified form of NpHR showed poor localization at the cell membrane. To achieve higher membrane-localization it was further modified by addition of a golgi export signal and membrane trafficking signal from a potassium channel (Kir2.1). The addition of Kir2.1 signal significantly improved the membrane localization of NpHR and this engineered form of NpHR was labeled eNpHR3.0 [5]


References

External links

  • Synthetic Neurobiology Group, MIT: Halorhodopsin mediating optical silencing of neurons
  • Medical Subject Headings (MeSH)
  • Optogenetics Resource Center
  • OpenOptogenetics.org, an open wiki about optogenetics.
  • families/superfamily-6 - Structures and orientations of bacterial rhodopsins in membrane

Template:Ion pumps

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.