Developing improved fluorescent protein voltage sensors
A protein activity sensor has the important advantage that it can be specifically expressed in an individual cell type in the brain. For the past 15 years or so we have been working to improve protein sensors of membrane potential.
The first human-made genetically encoded voltage indicator was a mosaic constructed by inserting a fluorescent protein (FP) into a voltage sensitive protein residing in the plasma membrane. The sensor, FlaSh, (Siegel and Isacoff 1997), was a voltage gated potassium channel with GFP inserted following the 6th transmembrane segment. Aside from its importance as a proof-of-principle, FlaSh had the useful feature of a steep, sigmoidal fluorescence vs voltage relationship that could be tuned to select for different ranges of membrane potential. However, FlaSh also had drawbacks; its signal was relatively slow (tau ~100 msec), and small (ΔF/F <5%). But, most importantly it worked in frog oocytes but not at all in mammalian cells. In mammalian cells, FlaSh’s expression, and that of two other first generation sensors that were also based on mammalian ion channels, was mainly intracellular (Baker, Lee et al. 2007). This obstacle was overcome by changing the membrane resident voltage sensor to the voltage sensitive domain of the sea squirt Ciona intestinalis voltage sensitive phosphatase (Dimitrov, He et al. 2007). The first member of this family, VFSP2.1, expressed well in the plasma membrane of mammalian cells and signaled changes in membrane potential. However, its signal was small (2% for a 100 mV depolarization) and slow (tau > 20 msec).
We have improved on the signal size (ArcLight in Jin et al 2012) and showed that ArcLight provides useful in vivo signals in the mammalian brain (Storace et al, 2015). In addition, we have examined a number of FRET constructs and found some with relatively large and fast responses. (Sung et al, 2015).
We are presently working to improve signal size and speed as well as developing sensors that will target specific subcellular membranes (dendrites, axon terminals and cell body).
- Developing Fast Fluorescent Protein Voltage Sensors by Optimizing FRET Interactions.Sung U, Sepehri-Rad M, Piao HH, Jin L, Hughes T, Cohen LB, Baker BJ. PLoS One. 2015; 2015 Nov 20. PMID: 26587834.
- Monitoring brain activity with protein voltage and calcium sensors.Storace DA, Braubach OR, Jin L, Cohen LB, Sung U. Sci Rep. 2015 May 13; 2015 May 13. PMID: 25970202.
- Mechanistic studies of the genetically encoded fluorescent protein voltage probe ArcLight.Han Z, Jin L, Chen F, Loturco JJ, Cohen LB, Bondar A, Lazar J, Pieribone VA. PLoS One. 2014; 2014 Nov 24. PMID: 25419571.
- Fluorescent protein voltage probes derived from ArcLight that respond to membrane voltage changes with fast kinetics.Han Z, Jin L, Platisa J, Cohen LB, Baker BJ, Pieribone VA. PLoS One. 2013; 2013 Nov 27. PMID: 24312287.
- Single action potentials and subthreshold electrical events imaged in neurons with a fluorescent protein voltage probe.Jin L, Han Z, Platisa J, Wooltorton JR, Cohen LB, Pieribone VA. Neuron. 2012 Sep 6. PMID: 22958819.
- Genetically encoded fluorescent voltage sensors using the voltage-sensing domain of Nematostella and Danio phosphatases exhibit fast kinetics.Baker BJ, Jin L, Han Z, Cohen LB, Popovic M, Platisa J, Pieribone V. J Neurosci Methods. 2012 Jul 15; 2012 May 24. PMID: 22634212.
- Random insertion of split-cans of the fluorescent protein venus into Shaker channels yields voltage sensitive probes with improved membrane localization in mammalian cells.Jin L, Baker B, Mealer R, Cohen L, Pieribone V, Pralle A, Hughes T. J Neurosci Methods. 2011 Jul 15; 2011 Apr 8. PMID: 21497167.
- Engineering and characterization of an enhanced fluorescent protein voltage sensor.Dimitrov D, He Y, Mutoh H, Baker BJ, Cohen L, Akemann W, Knöpfel T. PLoS One. 2007 May 9; 2007 May 9. PMID: 17487283.
- Three fluorescent protein voltage sensors exhibit low plasma membrane expression in mammalian cells.Baker BJ, Lee H, Pieribone VA, Cohen LB, Isacoff EY, Knopfel T, Kosmidis EK. J Neurosci Methods. 2007 Mar 30; 2006 Nov 28. PMID: 17126911.
- A genetically encoded optical probe of membrane voltage.Siegel MS, Isacoff EY. Neuron. 1997 Oct. PMID: 9354320.