Halobacterium salinarum, is similar to dunaliella and has the the bacteriorhodopsin.
Here is the baceriorhodopsin: this is a "Molecular assembler"
Bacteriorhodopsin (bR) is a 26~kDa transmembrane protein that acts as a light-driven proton pump in Halobacterium salinarum, converting light energy into a proton gradient. bR is the only protein constituent of the purple membrane (PM), a two-dimensional crystal lattice naturally present as part of the plasmic membrane of the bacterium. In addition to bR, PM contains ten haloarcheal lipids per protein unit that have identical saturated side chains, but differ in the nature of their polar heads. bR contains seven alpha-helices that enclose an all-trans retinal chromophore linked via a protonated Schiff base to residue Lys216. Upon light absorption, retinal undergoes an isomerization process that results under normal conditions in the translocation of a proton from the cytoplasmic side to the extracellular side of the membrane (quantum yield ~0.67). Vectorial proton translocation through membranes is a fundamental energy conversion process in biological cells. bR's utmost simplicity in comparison with other proton translocating, bioenergetic proteins makes it an ideal model for the study of this process.
Important Issues
A remarkable aspect of bR is that the minute details of its functioning are still subject of intense work and controversy, despite decades of research and impressive breakthroughs. One has today a possibility to solve many, if not all, of these problems as we have finally available high resolution structures of bR and, since very recently, of some of its photocycle intermediates on which the required physical analysis can be based. An explanation of bR's proton pumping requires necessarily an extrapolation from the known static structure and from other observational data. Proton translocation is a dynamic process and likely involves very minute motions partially below the resolution of observation, but accessible to molecular modeling. Methodological advances in modeling permit today to simulate integral membrane systems like the PM, as well as to provide highly accurate quantum chemical descriptions of potential surfaces for multiple (ground and excited) states, both preconditions for an explanation of bR's pump mechanism.
The Theoretical Biophysics Group works on three level of details of this molecular assembly:
* Structure and dynamics of the purple membrane.
* Structure and dynamics of the protein monomer.
* Quantum characterization of the retinal chromophore.
....." Halobacterium salinarum, converting light energy into a proton gradient. bR is the only protein constituent of the purple membrane (PM), a two-dimensional crystal lattice naturally present as part of the plasmic membrane of the bacterium."
www.ks.uiuc.edu/Research/newbr/Differences between Halobacterium salinarum and dunaliella:
Halobacterium salinarum:
Halobacterium salinarum - overview
Halobacterium salinarum
Introduction
Halobacterium_NaturalEnvironment
Halobacterium salinarum in its natural environment. The picture shows a salty pond in the Arabian desert, which is colored red due to the presence of Halobacterium salinarum.
Halobacterium salinarum is a model organism for the halophilic branch of the archaea. It is rod-shaped, motile, lives in highly saline environments (4M salt and higher), and is one of the few species known that can live in saturated salt solutions. Mass cultures of Halobacterium salinarum as shown in the pictures below can be recognized by their typical color, which originates from bacterioruberins. Halobacterium salinarum is depicted in its natural environment and as a species that colonizes salines.
Halobacterium_Saline
Massive growth of Halobacterium salinarum in a saline.
It can live with light as only energy source due to the activity of the retinal protein bacteriorhodopsin, a light-driven proton pump, which has been studied in great detail and has become a paradigm of membrane proteins in general and transport proteins in particular. From this point, our focus has widened to study additional processes in which retinal proteins are involved: the energy metabolism of Halobacterium salinarum and the tactic responses with its associated signal transduction network.
Since many years, research in the department of membrane biochemistry at the Max-Planck-Institute of Biochemistry concentrates on the biology of Halobacterium salinarum.
Retinal proteins of Halobacterium salinarum
Halobacterium salinarum contains four retinal proteins , which are photosynthetic pigments with a retinal chromophore involved in light energy conversion and signal transduction. The four retinal proteins are
* bacteriorhodopsin
(Haupts et. al. (1999), Oesterhelt (1998))
o the photosynthetic pigment that permits Halobacterium to grow with light as only energy source
o a light-driven proton pump which converts light energy into a proton gradient. The energy stored in the proton gradient can be used in different ways, e.g. for generation of ATP via ATP synthase
* halorhodopsin
(Kolbe et. al. (2000), Oesterhelt (1998))
o a light-driven chloride pump that permits Halobacterium to maintain the high internal salt concentration upon growth
* sensory rhodopsin I
o involved in phototaxis, mediates the photophilic response to orange and also the photophobic response to UV light
o forms a complex with the transducer protein htrI
* sensory rhodopsin II
o involved in phototaxis, mediates the photophobic response to blue light
o forms a complex with the transducer protein htrII
Energy metabolism
Halophiles, unlike their closest relatives, the methanogenes, can grow under aerobic and anaerobic conditions. Halobacterium has three distinct systems to gain energy.
* Oxidation of various metabolites under aerobic conditions
o oxidizes pyruvate which is channeled into the tricarboxylic acid cycle using pyruvate--ferredoxin oxidoreductase ( Plaga et. al. (1992))
o Halobacterium contains all five major complexes of the respiratory chain.
* Photosynthesis
o bacteriorhodopsin, a light-driven proton pump, creates a proton gradient. ATP synthase can use the energy of the proton gradient to drive ATP synthesis.
* Fermentation of argnine
o Halobacterium generates ATP by its arginine fermentation pathway.
Response to external stimuli (signal transduction)
electron microscope image of Halobacterium
An electron microscopic image of Halobacterium salinarum with ca 13.500-fold magnification. From the pole of the rod-shaped cell body extends the long flagellar bundle
Halobacterium is a flagellated organism which shows (chemo)tactic behaviour. Besides being able to detect essential amino acids (chemotaxis) and osmotically active compounds (osmotaxis), it can respond to light (phototaxis) and can sense oxygen (aerotaxis).
The signal transduction cascade starts with the receptor/transducer, which may be composed of two distinct proteins or may be a single protein. The signal is forwarded to the switch of the flagellar motor through a two-component regulatory system consisting of the histidine kinase cheA and the response regulator cheY. During relay of the signal it is amplified and different signals are integrated (see principles of a signal transduction). Adaptation involves methylation and demethylation of the transducer proteins by cheR (methyltransferase) and cheB (a regulated methylesterase). Genome analysis shows that Halobacterium contains 18 distinct transducers, indicating that it can sense a large number of distinct stimuli. Currently, stimuli are known seven of these transducers.
* two transducers are involved in phototaxis
o photophilic response: transducer protein htrI in combination with its photoreceptor sensorhodopsin I
o photophobic response: transducer protein htrII in combination with its photoreceptor sensorhodopsin II
* two transducers are involved in aerotaxis
o aerophilic response: transducer protein htrVIII
o aerophobic response: transducer protein hemAT
( Hou et. al. (2001))
* two transducers are involved in chemotaxis towards amino acids
o chemotactic response towards Arg: soluble transducer protein car
( Storch et. al. (1999))
o chemotactic response towards Leu, Ile, Val, Met, Cys: transducer protein basT in combination with periplasmic substrate binding protein basB
( Kokoeva et. al. (2000), Kokoeva et. al. (2002))
* one transducer is involved in chemotaxis towards osmolytes
o chemotactic response towards compatible osmolytes: transducer protein cosT in combination with periplasmic substrate binding protein cosB
( Kokoeva et. al. (2002))
* transducer mpcT is a membrane potential sensor
o this is involved in BR-mediated phototaxis
( Koch et. al. (2005))
Genome analysis
Halobacterium_Genome
A representation of the genome of Halobacterium salinarum. The 2 Mb chromosome is indicated as a set of three circles. Proteins are marked in the outer circle in a strand-specific manner. The central circle shows stable RNAs and the innter circle shows insertion elements.
The genome of Halobacterium salinarum has been unraveled twice. The genome of Halobacterium salinarum strain R1 has been sequenced by Oesterhelt et al. (unpublished, http://www.halolex.mpg.de). The genome of Halobacterium salinarum strain NRC-1 has been unraveled by Ng et al.. Halobacterium has a chromosome of 2 Mb having 68% GC and a number of megaplasmids with an average of 58% GC. Strain R1 has 4 megaplasmids and strain NRC-1 is reported to have 2 megaplasmids. Approximately 2,837 proteins are encoded by the whole genome of strain R1.
Note photos, and the references to flagellum, which could be the fibers, a flagellum by
itself might be immobile. But, if hooked to bacterium would be mobile.
www.biochem.mpg.de/en/rd/oesterhelt/web_page_list/Org_Hasal/Skytroll