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DTSTAMP:20261021T115516Z
LAST-MODIFIED:20150310T142118Z
DTSTART:20150320T140000Z
DTEND:20150320T150000Z
UID:event1425@bu.edu
URL:http://physics.bu.edu/internal/events/show/1425
SUMMARY:Vibrational Spectroscopy of an Optogenetic Rhodopsin: A Biophysical
	 Study of Molecular Mechanisms 
DESCRIPTION:Featuring John Ogren\n\nPart of the PhD Final Oral Exams.\n\nEx
	amining Committee: Ken Rothschild\, Shyam Erramilli\, Claudio Chamon\, Rob 
	Carey\, Jason Ritt (BME)\n\nAbstract:\nIn this dissertation\,the membrane p
	rotein channelrhodopsin-1 from the green flagellate algae Chlamydomonas agu
	stae (CaChR1) is studied using a variety of spectroscopic techniques develo
	ped in the Rothschild Molecular Biophysics Laboratory at Boston University.
	 Over the last decade\, channelrhodopsins have proven to be effective optog
	enetic tools due to their ability to function as light-gated ion channels w
	hen expressed in neurons. This ability allows neuroscientists to optically 
	activate an inward directed photocurrent which depolarizes the neuronal mem
	branes and triggers an action potential. Although a variety of channelrhodo
	psins with different properties have been used\, the underlying mechanisms 
	of channelrhodopsin functionality is not yet fully understood. The protein 
	studied here has several advantageous properties compared to the more exten
	sively studied channelrhodopsin-2 from Chlamydomonas reinhardtii including 
	a red shifted visible absorption and slower light inactivation despite havi
	ng a lower channel current. Elucidating the internal molecular mechanisms u
	nderlying the function of CaChR1 provides critical insight into the large c
	lass of channelrhodopsin proteins leading toward improved bioengineering fo
	r specific optogenetic applications. Here near-IR pre-resonance Raman spect
	roscopy of CaChR1 provides information on the structure of the unphotolyzed
	 (P0) retinal chromophore\, the Schiff base protonation state\, and presenc
	e of carboxylic acid residues interacting with the Schiff base. Low-tempera
	ture FTIR difference spectroscopy combined with site-directed mutagenesis a
	nd isotope labeling provide information on changes occurring in the retinal
	 chromophore and protein during the primary phototransition (P0→P1). This
	 includes information about changes involving protonation state of binding-
	pocket residues\, protein backbone structure\, and internal water molecules
	. Further experiments combining  low-temperature and time-resolved FTIR-dif
	ference spectroscopy reveal additional information about structural changes
	 during the transition from the unphotolyzed state to the active (open chan
	nel) state of the protein (P0→P2). This work has resulted in an initial m
	odel that describes key proton transfer events which occur between the Schi
	ff base and carboxylic acid residues inside the active site of CaChR1. The 
	model raises the possibility that ion channel gating and ion specificity is
	 regulated by the protonation changes of two key residues (Glu169 and Asp29
	9) located near the Schiff base.\n\n![John](/resources/event-image/1425/d8f
	d5fb_small)
LOCATION:PRB 261\, 3 Cummington Mall\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
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