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Ion-pumping microbial rhodopsins.

Kandori H - Front Mol Biosci (2015)

Bottom Line: Ion-transporting proteins can be found in microbial rhodopsins, such as light-gated channels and light-driven pumps, which are the main tools in optogenetics.On the other hand, different kinds of H(+) and Cl(-) pumps have been found in marine bacteria, such as proteorhodopsin (PR) and Fulvimarina pelagi rhodopsin (FR), respectively.In addition, a light-driven Na(+) pump was found, Krokinobacter eikastus rhodopsin 2 (KR2).

View Article: PubMed Central - PubMed

Affiliation: Department of Frontier Materials and OptoBioTechnology Research Center, Nagoya Institute of Technology Nagoya, Japan.

ABSTRACT
Rhodopsins are light-sensing proteins used in optogenetics. The word "rhodopsin" originates from the Greek words "rhodo" and "opsis," indicating rose and sight, respectively. Although the classical meaning of rhodopsin is the red-colored pigment in our eyes, the modern meaning of rhodopsin encompasses photoactive proteins containing a retinal chromophore in animals and microbes. Animal and microbial rhodopsins possess 11-cis and all-trans retinal, respectively, to capture light in seven transmembrane α-helices, and photoisomerizations into all-trans and 13-cis forms, respectively, initiate each function. Ion-transporting proteins can be found in microbial rhodopsins, such as light-gated channels and light-driven pumps, which are the main tools in optogenetics. Light-driven pumps, such as archaeal H(+) pump bacteriorhodopsin (BR) and Cl(-) pump halorhodopsin (HR), were discovered in the 1970s, and their mechanism has been extensively studied. On the other hand, different kinds of H(+) and Cl(-) pumps have been found in marine bacteria, such as proteorhodopsin (PR) and Fulvimarina pelagi rhodopsin (FR), respectively. In addition, a light-driven Na(+) pump was found, Krokinobacter eikastus rhodopsin 2 (KR2). These light-driven ion-pumping microbial rhodopsins are classified as DTD, TSA, DTE, NTQ, and NDQ rhodopsins for BR, HR, PR, FR, and KR2, respectively. Recent understanding of ion-pumping microbial rhodopsins is reviewed in this paper.

No MeSH data available.


Proposed local structures of KR2 in the dark (A) and in the M intermediate (B), suggested from crystal structures of KR2 at different pHs.
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Figure 12: Proposed local structures of KR2 in the dark (A) and in the M intermediate (B), suggested from crystal structures of KR2 at different pHs.

Mentions: These findings explain how Na+ is transported to the extracellular region across the protonated Schiff base of retinal. In the case of H+ transport by H+ pump rhodopsin, the H+ bound to the Schiff base itself is transported. In contrast, the transfer of H+ to the counterion (D116) upon M formation of KR2 transiently eliminates the positive charge in the Schiff base region, enabling the conduction of Na+ beside the Schiff base during the (L ⇄ M)-to-O process (Figure 11B). This scenario is strongly supported by recent crystal structures of KR2, which were determined at acidic and neutral pHs (Kato et al., 2015). Although there were few structural differences at different pHs, a change in the orientation of D116 was observed (Figure 12). Therefore, it is likely that D116 interacts with the protonated Schiff base in the unphotolyzed state, while protonated D116 newly interacts with N112 (and S70), allowing Na+ uptake from the cytoplasmic side by electrostatic neutralization (Kato et al., 2015). Upon formation of the red-shifted O intermediate, the Schiff base gains H+ again presumably from D116, and the ion-pair between the Schiff base and D116 inhibits the backward flow of transported Na+.


Ion-pumping microbial rhodopsins.

Kandori H - Front Mol Biosci (2015)

Proposed local structures of KR2 in the dark (A) and in the M intermediate (B), suggested from crystal structures of KR2 at different pHs.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4585134&req=5

Figure 12: Proposed local structures of KR2 in the dark (A) and in the M intermediate (B), suggested from crystal structures of KR2 at different pHs.
Mentions: These findings explain how Na+ is transported to the extracellular region across the protonated Schiff base of retinal. In the case of H+ transport by H+ pump rhodopsin, the H+ bound to the Schiff base itself is transported. In contrast, the transfer of H+ to the counterion (D116) upon M formation of KR2 transiently eliminates the positive charge in the Schiff base region, enabling the conduction of Na+ beside the Schiff base during the (L ⇄ M)-to-O process (Figure 11B). This scenario is strongly supported by recent crystal structures of KR2, which were determined at acidic and neutral pHs (Kato et al., 2015). Although there were few structural differences at different pHs, a change in the orientation of D116 was observed (Figure 12). Therefore, it is likely that D116 interacts with the protonated Schiff base in the unphotolyzed state, while protonated D116 newly interacts with N112 (and S70), allowing Na+ uptake from the cytoplasmic side by electrostatic neutralization (Kato et al., 2015). Upon formation of the red-shifted O intermediate, the Schiff base gains H+ again presumably from D116, and the ion-pair between the Schiff base and D116 inhibits the backward flow of transported Na+.

Bottom Line: Ion-transporting proteins can be found in microbial rhodopsins, such as light-gated channels and light-driven pumps, which are the main tools in optogenetics.On the other hand, different kinds of H(+) and Cl(-) pumps have been found in marine bacteria, such as proteorhodopsin (PR) and Fulvimarina pelagi rhodopsin (FR), respectively.In addition, a light-driven Na(+) pump was found, Krokinobacter eikastus rhodopsin 2 (KR2).

View Article: PubMed Central - PubMed

Affiliation: Department of Frontier Materials and OptoBioTechnology Research Center, Nagoya Institute of Technology Nagoya, Japan.

ABSTRACT
Rhodopsins are light-sensing proteins used in optogenetics. The word "rhodopsin" originates from the Greek words "rhodo" and "opsis," indicating rose and sight, respectively. Although the classical meaning of rhodopsin is the red-colored pigment in our eyes, the modern meaning of rhodopsin encompasses photoactive proteins containing a retinal chromophore in animals and microbes. Animal and microbial rhodopsins possess 11-cis and all-trans retinal, respectively, to capture light in seven transmembrane α-helices, and photoisomerizations into all-trans and 13-cis forms, respectively, initiate each function. Ion-transporting proteins can be found in microbial rhodopsins, such as light-gated channels and light-driven pumps, which are the main tools in optogenetics. Light-driven pumps, such as archaeal H(+) pump bacteriorhodopsin (BR) and Cl(-) pump halorhodopsin (HR), were discovered in the 1970s, and their mechanism has been extensively studied. On the other hand, different kinds of H(+) and Cl(-) pumps have been found in marine bacteria, such as proteorhodopsin (PR) and Fulvimarina pelagi rhodopsin (FR), respectively. In addition, a light-driven Na(+) pump was found, Krokinobacter eikastus rhodopsin 2 (KR2). These light-driven ion-pumping microbial rhodopsins are classified as DTD, TSA, DTE, NTQ, and NDQ rhodopsins for BR, HR, PR, FR, and KR2, respectively. Recent understanding of ion-pumping microbial rhodopsins is reviewed in this paper.

No MeSH data available.