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Rhodopsin
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Overview
Structure and mechanics
Main classes of rhodopsin
Recent developments
Eukaryotes
 Bacteria
 Material Science
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Rhodopsin Overview
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Membrane protein that binds retinal to form a light
absorbing pigment (AKA: retinylidene proteins)
Over 300 versions of rhodopsin found so far
Diverse functions:
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Light sensitive protein found in all animal eyes
Light driven proton pump
Light driven chloride pump
Phototaxis receptors
Close relatives: a heat shock protein, a
translocase in mitochondria
Structure and Mechanics
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All have the same physical structure and mechanics
Seven trans-membrane alpha helices
Retinal attached by Schiff base linkage to a lysine
residue in the seventh helix in all known cases
Structural changes induced by binding retinal are similar
Two distinct rhodopsin families: Type 1 and Type 2
Look and act the same but the gene sequence is quite
different
http://www.prism.gatech.edu/~gt7966a/research.html
Bacteriorhodopsin
http://anx12.bio.uci.edu/~hudel/br/index.html
Bacteriorhodopsin
Ground state on left, bleached state on right
http://anx12.bio.uci.edu/~hudel/br/index.html
Main classes of rhodopsin
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Type 1 Rhodopsins
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First observed in 1971 in the archaea Halobacterium
Salinarum
Note: archaea were classed with bacteria in '71
Type 2 Rhodopsins
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Photosensitive receptor proteins in animal eyes
Receptor proteins in other tissues in early branching
vertebrates
Receptor proteins found in human and mouse brains
Type 1 Rhodopsins
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Bacteriorhodopsin:
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Halorhodopsin:
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Each photocycle pumps one proton out of the cytoplasm
Increases proton gradient to drive ATPsynthase
Change in pH converts to chloride pump
Each photocycle pumps one chloride ion out of the
cytoplasm
Change in pH converts to proton pump
Sensory Rhodopsin 1:
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Works with bound accessory protein to initiate motility
cascade
Removal of accessory protein converts to proton pump
Recent developments
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Type 1 Rhodopsins have been found in
eukaryotes
Several filamentous fungi
 Several algae
 A yeast
 Fungus zoospores
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Proteorhodopsin, a bacteriorhodopsin like
protein, recently discovered in marine bacteria
Discovery of Proteorhodopsin
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Sequenced large gene fragment from
uncultivated marine bacteria group (SAR 86)
Gene fragment included 16s rRNA gene and
ORF for bacteriorhodopsin
No other archaeal ORFs found in fragment
Proteorhodopsin verified
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Study 1:
Protein expressed in E. coli
 E. coli turned reddish
 Absorbed same frequency of light as
bacteriorhodopsin
 Light induced acidification
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Proteorhodopsin verified
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Study 2:
Membranes from native marine bacteria used
 Showed same absorbance peaks
 Same light induced acidification
 Bacteria from different areas had different
absorbance peaks
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Proteorhodopsin is an important source of energy
for SAR68 bacteria
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Proteorhodopsin is highly expressed
Proteorhodopsin tuned for each environment
Many genetic variants have been found
Carbon Flow in the Ocean
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SAR86 bacteria are abundant and widespread
Can live where food is scarce
 Become food for others
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SAR86 bacteria are related to chemolithoautotrophs
Photoheterotrophic lifestyle?
 New form of photoautotrophy?
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Uses of Bacteriorhodopsin
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Discovery of bacteriorhodopsin has opened a whole
new field in materials science
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optically addressed spatial light modulators
real-time interferometry
holographic pattern recognition
optical data storage
all-optical logic gates (light driven computers)
Dieter Oesterhelt discovered bacteriorhodopsin in
1971 and was still publishing research on it as late
as 1994.
References
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5/23/2017
Spudich, J.L., Yang, C.S. Jung, K. H., & Spudich, E. N.
Retinylidene proteins: Structures and functions from archaea to humans.
Annu. Rev. Cell Dev. Biol. 16, 365-392 (2000).
Oesterhelt D., & Stoeckenius, W.
Rhodopsin like protein from the purple membrane of Halobacterium halobium
Nature 233, 149-152 (1971)
Beja, O., Aravind, L., Koonin, V., Suzuki, M., Hadd, A., Nguyen, L., Jovanovich, S., Gates, C.,
Feldman, R., Spudich, J., Spudich, E. & DeLong, E.
Bacterial Rhodopsin: Evidence for a New Type of Phototrophy in the Sea
Science 289, 1902-1906 (2000)
Beja, O., DeLong, E., Spudich, J., Leclerc, M. & DeLong, E.
Proteorhodopsin phototrophy in the ocean
Nature 411, 786-789 (2001)
Hampp, N., Thoma, R. & Bräuchle, Kreuzer, C.F.-H., Maurer, R., & Oesterhelt, D.
Bacteriorhodopsin variants for optical information processing: A new approach in material science
AIP Conference Proceedings -- July 20, 1992 -- Volume 262, Issue 1, pp. 181-190
Zhang, T., Zhang, C., Fu, G., Li, Y., Gu, L., Zhang, G., Song, Q. W., Parsons, B., Birge, R.
All-optical logic gates using bacteriorhodopsin films
Optical Engineering -- February 2000 -- Volume 39, Issue 2, pp. 527-534
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