Sensory rhodopsin II (SRII), also known as ''pharaonis'' phoborhodopsin (''p''pR), is a
membrane protein
Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Integral membrane proteins are a permanent part of a cell membrane ...
of
archaea, responsible generating the
phototaxis
Phototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves towards or away from a stimulus of light. This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive l ...
signal. Sensory rhodopsin II is found in ''
Halobacterium salinarum
''Halobacterium salinarum'', formerly known as ''Halobacterium cutirubrum'' or ''Halobacterium halobium'', is an extremely halophilic marine obligate aerobic archaeon. Despite its name, this is not a bacterium, but a member of the domain Archaea. ...
'' and ''
Natronomonas pharaonis
''Natronomonas'' (common abbreviation ''Nmn.'').
is a genus of the Halobacteriaceae.See the NCBIbr>webpage on Natronomonas Data extracted from the
Description and significance
''Natronomonas pharaonis'' is an aerobic, extremely haloalkaliph ...
''.
Structure
Structure of sensory rhodopsin II is typical for
microbial rhodopsin
Microbial rhodopsins, also known as bacterial rhodopsins are retinal-binding proteins that provide light-dependent ion transport and sensory functions in halophilic
and other bacteria. They are integral membrane proteins with seven transmembr ...
. It consists of seven
transmembrane
A transmembrane protein (TP) is a type of integral membrane protein that spans the entirety of the cell membrane. Many transmembrane proteins function as gateways to permit the transport of specific substances across the membrane. They frequentl ...
a-helices
The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid located four residues earli ...
with
retinal
Retinal (also known as retinaldehyde) is a polyene chromophore. Retinal, bound to proteins called opsins, is the chemical basis of visual phototransduction, the light-detection stage of visual perception (vision).
Some microorganisms use re ...
molecule connected via
Schiff base
In organic chemistry, a Schiff base (named after Hugo Schiff) is a compound with the general structure ( = alkyl or aryl, but not hydrogen). They can be considered a sub-class of imines, being either secondary ketimines or secondary aldimine ...
to
K205. Notable feature of sensory rhodopsin II is presence of charged
residue Y199 on the surface of the
hydrophobic
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, ...
region. This residue is responsible for binding of sensory rhodopsin II transducer protein - HtrII. HtrII consists of two transmembrane helices, two
HAMP-domains and methyl-accepting signalling domain. In case of ''
Halobacterium salinarum
''Halobacterium salinarum'', formerly known as ''Halobacterium cutirubrum'' or ''Halobacterium halobium'', is an extremely halophilic marine obligate aerobic archaeon. Despite its name, this is not a bacterium, but a member of the domain Archaea. ...
'' HtrII also comprises extracellular chemosensor region, which is responsible for
serine
Serine (symbol Ser or S) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated − form under biological conditions), a carboxyl group (which is in the deprotonated − for ...
sensing.
Function
SRII in the
plasma membrane
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...
binds its transducer via a number of
bonds
Bond or bonds may refer to:
Common meanings
* Bond (finance), a type of debt security
* Bail bond, a commercial third-party guarantor of surety bonds in the United States
* Chemical bond, the attraction of atoms, ions or molecules to form chemical ...
.
Photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are Massless particle, massless ...
absorption induces structural changes in SRII, which when conducted to HtrII. HtrII in turn regulates level of unbound
kinase
In biochemistry, a kinase () is an enzyme that catalysis, catalyzes the transfer of phosphate groups from High-energy phosphate, high-energy, phosphate-donating molecules to specific Substrate (biochemistry), substrates. This process is known as ...
s in
cytoplasm
In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...
. Kinases regulate rotation of
flagella
A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates.
A microorganism may have f ...
via phosphorylation. Thus phototaxis signal is converted in bacteria' motion.
Further reading
*
* {{Cite journal, last1 = Sasaki , first1 = J., last2 = Spudich , first2 = J., title = Signal transfer in haloarchaeal sensory rhodopsin- transducer complexes, journal = Photochemistry and Photobiology, volume = 84, issue = 4, pages = 863–868, year = 2008, pmid = 18346091 , doi = 10.1111/j.1751-1097.2008.00314.x
7TM receptors
Transmembrane receptors
Cell signaling
Integral membrane proteins