The crystal structures of a chloride-pumping microbial rhodopsin and its proton-pumping mutant illuminate proton transfer determinants

Abstract

Microbial rhodopsins are versatile and ubiquitous retinal-binding proteins that function as light-driven ion pumps, light-gated ion channels, and photosensors, with potential utility as optogenetic tools for altering membrane potential in target cells. Insights from crystal structures have been central for understanding proton, sodium, and chloride transport mechanisms of microbial rhodopsins. Two of three known groups of anion pumps, the archaeal halorhodopsins (HRs) and bacterial chloride-pumping rhodopsins, have been structurally characterized. Here we report the structure of a representative of a recently discovered third group consisting of cyanobacterial chloride and sulfate ion-pumping rhodopsins, the Mastigocladopsis repens rhodopsin (MastR). Chloride-pumping MastR contains in its ion transport pathway a unique Thr-Ser-Asp (TSD) motif, which is involved in the binding of a chloride ion. The structure reveals that the chloride-binding mode is more similar to HRs than chloride-pumping rhodopsins, but the overall structure most closely resembles bacteriorhodopsin (BR), an archaeal proton pump. The MastR structure shows a trimer arrangement reminiscent of BR-like proton pumps and shows features at the extracellular side more similar to BR than the other chloride pumps. We further solved the structure of the MastR-T74D mutant, which contains a single amino acid replacement in the TSD motif. We provide insights into why this point mutation can convert the MastR chloride pump into a proton pump but cannot in HRs. Our study points at the importance of precise coordination and exact location of the water molecule in the active center of proton pumps, which serves as a bridge for the key proton transfer. Microbial rhodopsins are versatile and ubiquitous retinal-binding proteins that function as light-driven ion pumps, light-gated ion channels, and photosensors, with potential utility as optogenetic tools for altering membrane potential in target cells. Insights from crystal structures have been central for understanding proton, sodium, and chloride transport mechanisms of microbial rhodopsins. Two of three known groups of anion pumps, the archaeal halorhodopsins (HRs) and bacterial chloride-pumping rhodopsins, have been structurally characterized. Here we report the structure of a representative of a recently discovered third group consisting of cyanobacterial chloride and sulfate ion-pumping rhodopsins, the Mastigocladopsis repens rhodopsin (MastR). Chloride-pumping MastR contains in its ion transport pathway a unique Thr-Ser-Asp (TSD) motif, which is involved in the binding of a chloride ion. The structure reveals that the chloride-binding mode is more similar to HRs than chloride-pumping rhodopsins, but the overall structure most closely resembles bacteriorhodopsin (BR), an archaeal proton pump. The MastR structure shows a trimer arrangement reminiscent of BR-like proton pumps and shows features at the extracellular side more similar to BR than the other chloride pumps. We further solved the structure of the MastR-T74D mutant, which contains a single amino acid replacement in the TSD motif. We provide insights into why this point mutation can convert the MastR chloride pump into a proton pump but cannot in HRs. Our study points at the importance of precise coordination and exact location of the water molecule in the active center of proton pumps, which serves as a bridge for the key proton transfer. One of the foremost challenges in understanding functional diversity of microbial rhodopsins is dissecting their complex structure–function relationships (1Ernst O.P. Lodowski D.T. Elstner M. Hegemann P. Brown L.S. Kandori H. Microbial and animal rhodopsins: structures, functions, and molecular mechanisms.Chem. Rev. 2014; 114 (24364740): 126-16310.1021/cr4003769Crossref PubMed Scopus (535) Google Scholar, 2Kurihara M. Sudo Y. Microbial rhodopsins: wide distribution, rich diversity and great potential.Biophys. Physicobiol. 2015; 12 (27493861): 121-12910.2142/biophysico.12.0_121Crossref PubMed Google Scholar, 3Govorunova E.G. Sineshchekov O.A. Li H. Spudich J.L. Microbial rhodopsins: diversity, mechanisms, and optogenetic applications.Annu. Rev. Biochem. 2017; 86 (28301742): 845-87210.1146/annurev-biochem-101910-144233Crossref PubMed Scopus (129) Google Scholar, 4Gushchin I. Gordeliy V. Microbial rhodopsins.Subcell. Biochem. 2018; 87 (29464556): 19-5610.1007/978-981-10-7757-9_2Crossref PubMed Scopus (19) Google Scholar, 5Klare J.P. Chizhov I. Engelhard M. Microbial rhodopsins: scaffolds for ion pumps, channels, and sensors.Results Probl. Cell Differ. 2008; 45 (17898961): 73-12210.1007/400_2007_041Crossref PubMed Scopus (75) Google Scholar). Despite the distinct functional roles and different amino acid sequences, microbial rhodopsins have surprisingly similar structures, especially in their transmembrane domains frugally recycled by nature. It turns out that the functional differences among microbial rhodopsins are regulated by relatively small variations in the side chains, internal water molecules, and bound ions, which necessitate the acquisition of high-resolution structural data to probe structure–function relationships. This is particularly true for ion-pumping rhodopsins, a structurally uniform group with various ion specificities, whereas greater structural diversity has been seen in sensory rhodopsins, enzymerhodopsins, and channelrhodopsins (3Govorunova E.G. Sineshchekov O.A. Li H. Spudich J.L. Microbial rhodopsins: diversity, mechanisms, and optogenetic applications.Annu. Rev. Biochem. 2017; 86 (28301742): 845-87210.1146/annurev-biochem-101910-144233Crossref PubMed Scopus (129) Google Scholar, 6Mukherjee S. Hegemann P. Broser M. Enzymerhodopsins: novel photoregulated catalysts for optogenetics.Curr. Opin. Struct. Biol. 2019; 57 (30954887): 118-12610.1016/j.sbi.2019.02.003Crossref PubMed Scopus (16) Google Scholar). Ion-pumping microbial rhodopsins are widespread among Eukarya, Bacteria, and Archaea (7Kandori H. Ion-pumping microbial rhodopsins.Front. Mol. Biosci. 2015; 2 (26442282): 5210.3389/fmolb.2015.00052Crossref PubMed Scopus (64) Google Scholar, 8Pinhassi J. DeLong E.F. Béjà O. González J.M. Pedrós-Alió C. Marine bacterial and archaeal ion-pumping rhodopsins: genetic diversity, physiology, and ecology.Microbiol. Mol. Biol. Rev. 2016; 80 (27630250): 929-95410.1128/MMBR.00003-16Crossref PubMed Scopus (84) Google Scholar, 9Brown L.S. Jung K.H. Bacteriorhodopsin-like proteins of eubacteria and fungi: the extent of conservation of the haloarchaeal proton-pumping mechanism.Photochem. Photobiol. Sci. 2006; 5 (16761082): 538-54610.1039/b514537fCrossref PubMed Scopus (61) Google Scholar). These microbial rhodopsins share a similar structural template consisting of seven tightly bundled transmembrane α-helices with the N and C termini located outside and inside the cell, respectively (Fig. 1). The all-trans-retinal chromophore is covalently bound through a protonated retinal Schiff base (PRSB) linkage to the ε-amino group of a lysine residue in the middle of the seventh helix. For ion pumps, the absorption of a photon triggers the retinal chromophore to isomerize from all-trans- to 13-cis-configuration, which induces a photocycle involving protein structural changes to pump an ion through the membrane against a concentration gradient. Despite their similar overall architecture, ion specificities and transport vectorialities of these rhodopsins can be adjusted by fine-tuning their structures (10Muroda K. Nakashima K. Shibata M. Demura M. Kandori H. Protein-bound water as the determinant of asymmetric functional conversion between light-driven proton and chloride pumps.Biochemistry. 2012; 51 (22583333): 4677-468410.1021/bi300485rCrossref PubMed Scopus (40) Google Scholar, 11Inoue K. Nomura Y. Kandori H. Asymmetric functional conversion of eubacterial light-driven ion pumps.J. Biol. Chem. 2016; 291 (26929409): 9883-989310.1074/jbc.M116.716498Abstract Full Full PubMed Scopus Google proteins to pump other a of three the third transmembrane has been as a function determinant for ion-pumping rhodopsins K. Y. Kandori H. rhodopsins in 2015; Full Full PubMed Scopus Google Scholar, O. for microbial rhodopsin ion Sci. 2014; PubMed Scopus Google Scholar). and pumps have an motif, whereas bacterial pumps more have a the proton the and the proton its retinal-binding pumps an motif, in which the three roles in binding and in the K. M. Kandori H. The of the in Chem. 2015; PubMed Scopus Google Scholar). the of pumps, anion have a and are by at three archaeal pumps have a motif, whereas recently discovered eubacterial chloride-pumping rhodopsins an in groups the amino of the a chloride anion in the C. Chizhov I. Engelhard M. Microbial light-driven chloride Rev. 2018; PubMed Scopus Google Scholar, S. Y. M. K. structure of the light-driven chloride pump from Mol. Biol. PubMed Scopus Google Scholar, M. J. of from in a crystal that the Struct. Biol. 2015; PubMed Scopus Google Scholar, K. H. structure and functional of a light-driven chloride pump an 2016; PubMed Scopus Google Scholar, S. Y. M. DeLong E.F. K. S. M. for light-driven transport by a of chloride ion Biol. Chem. 2016; 291 Full Full PubMed Scopus Google Scholar). is a novel distinct cyanobacterial rhodopsin group chloride and sulfate which have to HRs and Demura M. of a cyanobacterial chloride-pumping rhodopsin and its conversion into a proton Biol. Chem. 2016; 291 Full Full PubMed Scopus Google Scholar, S. M. S. Y. M. H. Y. Sudo Y. of a light-driven and its Chem. 2017; PubMed Scopus Google Scholar, Y. Y. Y. J. Demura M. K. Sudo Y. S. of a haloarchaeal pump in 2018; PubMed Scopus Google Scholar, M. J. Brown L.S. of the unique of chloride transport by a cyanobacterial Chem. Chem. 2018; PubMed Google Scholar). to this group and as the but has as its third with a of unique The of this group is Mastigocladopsis repens rhodopsin which pumps chloride through a TSD Demura M. of a cyanobacterial chloride-pumping rhodopsin and its conversion into a proton Biol. Chem. 2016; 291 Full Full PubMed Scopus Google Scholar, M. J. Brown L.S. of the unique of chloride transport by a cyanobacterial Chem. Chem. 2018; PubMed Google Scholar). high-resolution structures of representative HRs S. Y. M. K. structure of the light-driven chloride pump from Mol. Biol. PubMed Scopus Google Scholar, M. J. of from in a crystal that the Struct. Biol. 2015; PubMed Scopus Google and K. H. structure and functional of a light-driven chloride pump an 2016; PubMed Scopus Google Scholar, S. Y. M. DeLong E.F. K. S. M. for light-driven transport by a of chloride ion Biol. Chem. 2016; 291 Full Full PubMed Scopus Google are the third group of chloride-pumping rhodopsins has been to proton-pumping rhodopsins, of structures of chloride-pumping rhodopsins with the function the ion in structural of this function and its fine-tuning this we provide the high-resolution crystal structure of the chloride-pumping which reveals the unique structural of this novel anion with the chloride-binding in the of a BR-like structural to understanding key structural of the of microbial rhodopsin ion pumps is their functional in which a rhodopsin of is to a different conversion of ion pumps has been with through the three amino at the (10Muroda K. Nakashima K. Shibata M. Demura M. Kandori H. Protein-bound water as the determinant of asymmetric functional conversion between light-driven proton and chloride pumps.Biochemistry. 2012; 51 (22583333): 4677-468410.1021/bi300485rCrossref PubMed Scopus (40) Google Scholar, 11Inoue K. Nomura Y. Kandori H. Asymmetric functional conversion of eubacterial light-driven ion pumps.J. Biol. Chem. 2016; 291 (26929409): 9883-989310.1074/jbc.M116.716498Abstract Full Full PubMed Scopus Google Scholar, Demura M. of a cyanobacterial chloride-pumping rhodopsin and its conversion into a proton Biol. Chem. 2016; 291 Full Full PubMed Scopus Google Scholar, J. Brown L.S. Kandori H. of bacteriorhodopsin into a chloride ion PubMed Scopus Google Scholar). this we the structures of chloride-pumping MastR and its proton-pumping in the of other chloride and proton pumps with known high-resolution The structures that the of the and water for MastR and the that proton transport a water and a Schiff It that the BR-like structure of which of the water molecule with the Schiff for its functional conversion to a proton in to HRs in which this is structural for proton by microbial rhodopsins. We MastR and the MastR-T74D in (Fig. and the proteins the S. a for membrane proteins a bacteriorhodopsin Mol. Biol. PubMed Scopus Google Scholar). We (Fig. and in which of three in a (Fig. C and to that of other (Fig. and MastR as (Fig. and MastR-T74D as (Fig. the MastR (Fig. whereas MastR-T74D (Fig. This in in MastR an asymmetric with rhodopsins their extracellular whereas MastR-T74D contains a single protein in the asymmetric (Fig. We the crystal structures of MastR and MastR-T74D at of and respectively (Fig. and other microbial rhodopsins, MastR has seven transmembrane by three and three extracellular (Fig. The and C a The structure contains 45 water molecules, chloride ions, a from and the retinal The of the chromophore retinal in the (Fig. covalently bound to the ε-amino group of a in with M. J. Brown L.S. of the unique of chloride transport by a cyanobacterial Chem. Chem. 2018; PubMed Google Scholar). The MastR and MastR-T74D structures are with an of and in the the of the mutation and the of for the and mutant, respectively (Fig. and The MastR structure further shows chloride the and the other a crystal between the of The ion the is between a single water molecule and and of the TSD as by the in The ion is the of the and to a water This chloride can be by and but as by absorption (Fig. Demura M. of a cyanobacterial chloride-pumping rhodopsin and its conversion into a proton Biol. Chem. 2016; 291 Full Full PubMed Scopus Google Scholar). The mutation to chloride of 2 to but ion whereas the mutation the and of the M. J. Brown L.S. of the unique of chloride transport by a cyanobacterial Chem. Chem. 2018; PubMed Google and the mutation chloride Y. S. Demura M. study of a cyanobacterial 2019; PubMed Scopus Google Scholar). This with the which that and are involved in ion similar to M. J. of from in a crystal that the Struct. Biol. 2015; PubMed Scopus Google Scholar). The chloride is by the extracellular of MastR (Fig. ion is to bridge by with the of and of of This ion to be a and be a ion as from (Fig. and the MastR-T74D MastR-T74D as the into and the of for a ion the chloride crystal between (Fig. of MastR are by of of with and of (Fig. The is by three the of with the group of a between and and a between and the of at the are by and (Fig. The structure of microbial rhodopsins in can be by the of the retinal to distinct M. K. K. M. M. C. Kandori H. of microbial rhodopsins by and 2018; PubMed Scopus Google Scholar). rhodopsins and a single rhodopsins with a at the side of the and a the side of rhodopsins, the different of the to an with the and the and of We the of which a at and a at to its of that in (Fig. The in the MastR crystal is in and of archaeal rhodopsins as BR H. J.P. of bacteriorhodopsin at Mol. Biol. 291 PubMed Scopus Google Scholar, The structure of the membrane from of the Mol. Biol. PubMed Scopus Google M. H. of the light-driven chloride pump at PubMed Scopus Google and K. of in the structure of Mol. Biol. 2008; PubMed Scopus Google Scholar). BR-like trimer for sensory rhodopsin by S. I. Jung K.H. Brown L.S. V. structure of a membrane PubMed Scopus Google Scholar). the at the MastR to be for the trimer S. I. Jung K.H. Brown L.S. V. structure of a membrane PubMed Scopus Google and are than for BR and MastR as a trimer in (Fig. whereas BR into and of bacteriorhodopsin in the and PubMed Scopus Google Scholar). This why in similar MastR a whereas BR as S. a for membrane proteins a bacteriorhodopsin Mol. Biol. PubMed Scopus Google Scholar). The BR-like structure of MastR is in to for eubacterial as chloride-pumping rhodopsin K. Y. Kandori H. study of a light-driven chloride ion pump from Chem. 2014; PubMed Scopus Google for which a M. K. K. M. M. C. Kandori H. of microbial rhodopsins by and 2018; PubMed Scopus Google as as eubacterial pumps of the and of a novel of Biol. 5 PubMed Scopus (64) Google as rhodopsin 2 K. H. S. H. K. Kandori H. light-driven ion pump in PubMed Scopus Google and eubacterial proton pumps rhodopsin K. Kandori H. Brown L.S. O.P. structure and of 2019; PubMed Scopus Google and Y. Sineshchekov O.A. Spudich J.L. H. with the in Biol. PubMed Scopus Google Scholar). The crystal structures of the eubacterial K. H. structure and functional of a light-driven chloride pump an 2016; PubMed Scopus Google Scholar, S. Y. M. DeLong E.F. K. S. M. for light-driven transport by a of chloride ion Biol. Chem. 2016; 291 Full Full PubMed Scopus Google and pumps K. Y. H. M. S. H. J. S. K. M. for transport by a light-driven 2015; PubMed Scopus Google Scholar, K. V. I. V. V. S. V. Gordeliy V. and mechanisms of 2019; 5 PubMed Google have as a an and a motif, which in a of the in the of and (Fig. It has been that the of the the in eubacterial pumps K. Kandori H. Brown L.S. O.P. structure and of 2019; PubMed Scopus Google Scholar). MastR have these structural features and as a trimer the structures of known chloride pumps are with MastR and differences are at the extracellular side the ion is located (Fig. the transmembrane of and MastR similar different from the of the and of the to different of the chloride ion is for MastR as by the in This is to MastR the than the proton pump BR with which MastR shows overall structural the extracellular HRs have that most of the extracellular and small are that as for has the which with an the membrane a that to a of between the active center and the extracellular S. Y. M. K. structure of the light-driven chloride pump from Mol. Biol. PubMed Scopus Google Scholar). residue in the middle of is for the J. and of Chem. PubMed Scopus Google Scholar). The to be an that chloride pumps to the of The chloride pathway is in the MastR is an into a The is located between the and and is to as the chloride This is by and which as a similar to the proton pathway regulated by the and in BR Brown L.S. K. binding a membrane protein by a protonated water Sci. PubMed Scopus Google Scholar). to of of MastR to be to the Schiff base its replacement chloride Y. S. Demura M. study of a cyanobacterial 2019; PubMed Scopus Google Scholar). in the photocycle be for chloride a mutation of to the the and the photocycle M. J. Brown L.S. of the unique of chloride transport by a cyanobacterial Chem. Chem. 2018; PubMed Google which chloride from the extracellular This is in with the and M. J. Brown L.S. of the unique of chloride transport by a cyanobacterial Chem. Chem. 2018; PubMed Google which photocycle these are the and are located between and the the by and with a single water a small to the retinal this ion the which has small with a single water molecule in We that the chloride is more to the which is by and which are for binding This is in with the other which and as potential chloride It that the mutation in of the and N which the overall photocycle by a of M. J. Brown L.S. of the unique of chloride transport by a cyanobacterial Chem. Chem. 2018; PubMed Google Scholar). is of the chloride similar to the of HRs M. and anion binding and transport in the light-driven chloride pump J. PubMed Scopus Google Scholar). The a with which to in the mutant, the residue is known to a key in changes in other microbial rhodopsins in a membrane transport from crystal structures of the in the bacteriorhodopsin PubMed Scopus Google Scholar). to the other we a and which and particularly is between and between the which is with the of these by M. J. Brown L.S. of the unique of chloride transport by a cyanobacterial Chem. Chem. 2018; PubMed Google Scholar). the that in to the chloride and be in the for the photocycle to The for that be to the of the that the of is regulated by its with and which as a of from changes as for that is an of a which are three in and (Fig. is located to the and and a with the of between the is This be further structural ion the is located to the of retinal and to be involved in of the of the is to the by to which the water with we that the ion is through the pathway by and these are for the of and an of the and photocycle is among cyanobacterial ion pumps but is in BR and HRs M. J. Brown L.S. of the unique of chloride transport by a cyanobacterial Chem. Chem. 2018; PubMed Google Scholar). the and are and which in ion understanding of the chloride transport and pathway structural the photocycle The most structural differences between MastR and MastR-T74D to the retinal chromophore as in the MastR a ion is located between the groups of and of the TSD motif. This ion is of an in which the ion is to the and side chains, as as an water molecule to the and the group of The and side further an (Fig. The MastR-T74D in contains ion in the retinal-binding The side of the the ion is located in MastR and the function of the ion in the The between and is the group from (Fig. This is in with the for the side in other proton (Fig. and chloride pumps (Fig. in which points the extracellular for the and retinal for the The different of the in and in different absorption with of for MastR-T74D and for respectively (Fig. Demura M. of a cyanobacterial chloride-pumping rhodopsin and its conversion into a proton Biol. Chem. 2016; 291 Full Full PubMed Scopus Google Scholar). of MastR is that a of the TSD to the chloride pump into proton pump Demura M. of a cyanobacterial chloride-pumping rhodopsin and its conversion into a proton Biol. Chem. 2016; 291 Full Full PubMed Scopus Google Scholar). functional conversion of archaeal and chloride pumps into proton pumps by altering their The of single to various proton pumps with an as proton (10Muroda K. Nakashima K. Shibata M. Demura M. Kandori H. Protein-bound water as the determinant of asymmetric functional conversion between light-driven proton and chloride pumps.Biochemistry. 2012; 51 (22583333): 4677-468410.1021/bi300485rCrossref PubMed Scopus (40) Google Scholar, structure of at Mol. Biol. PubMed Scopus Google Scholar, Brown L.S. transport by PubMed Scopus Google the is for BR proton pump. the other conversion of BR in the to ion by the from to TSD the chloride pump J. Brown L.S. Kandori H. of bacteriorhodopsin into a chloride ion PubMed Scopus Google Scholar, J. C. and proton transport in bacteriorhodopsin different of ion in a retinal Mol. Biol. PubMed Scopus Google Scholar). for eubacterial pumps, conversion in For an chloride mutation of to to a proton but conversion of a proton into a chloride pump by mutation of to K. Nomura Y. Kandori H. Asymmetric functional conversion of eubacterial light-driven ion pumps.J. Biol. Chem. 2016; 291 (26929409): 9883-989310.1074/jbc.M116.716498Abstract Full Full PubMed Scopus Google Scholar). The of functional conversion that the pumps have a transport and the of proton and chloride pumps domains of L.S. Jung K.H. Bacteriorhodopsin-like proteins of eubacteria and fungi: the extent of conservation of the haloarchaeal proton-pumping mechanism.Photochem. Photobiol. Sci. 2006; 5 (16761082): 538-54610.1039/b514537fCrossref PubMed Scopus (61) Google Scholar, K. I. Y. Y. Y. of the archaeal rhodopsins: changes by and functional Mol. Biol. PubMed Scopus Google Scholar, Spudich J.L. Microbial rhodopsins: functional and genetic 2006; Full Full PubMed Scopus Google Scholar). structural of proton and chloride pumps can provide insights into why are but are (Fig. The to the is at the of the retinal the of the in chloride pumps, and for proton-pumping rhodopsins the proton for proton to the proton The of the the point in the and is a determinant of pump we the of proton pumps (Fig. C and we that in a central water molecule the and the side of the proton in and a in BR (7Kandori H. Ion-pumping microbial rhodopsins.Front. Mol. Biosci. 2015; 2 (26442282): 5210.3389/fmolb.2015.00052Crossref PubMed Scopus (64) Google is that these are between the than to proton pumps the is by water and side the amino acid of the motif. For the chloride pumps the is similar but in contains a ion between the amino of the motif, which is a water molecule to the (Fig. and It is that the are especially the between the central water and which is for archaeal HRs and eubacterial For MastR the is more similar to proton pumps, which with the overall structural between MastR and the proton pump be an for why the to ion pump conversion of the water from to be a for proton and is with the structural data the in (10Muroda K. Nakashima K. Shibata M. Demura M. Kandori H. Protein-bound water as the determinant of asymmetric functional conversion between light-driven proton and chloride pumps.Biochemistry. 2012; 51 (22583333): 4677-468410.1021/bi300485rCrossref PubMed Scopus (40) Google Scholar). The of the water in the to be for a proton between the proton and the which the of the is for a proton in of the the structures, we that in BR is an determinant to the of the This residue is a in the proton as K. S. Y. Nomura Y. Shibata M. Kandori H. light-driven proton 2016; PubMed Scopus Google and K. M. S. S. M. H. Béjà O. Kandori H. a of rhodopsins from that function as light-driven PubMed Scopus Google (Fig. that the side of is to changes of the complex the photocycle to proton to the L.S. Y. M. Y. The retinal Schiff complex of the photocycle is a of proton to PubMed Scopus (61) Google Scholar). the of and in BR by the mutation of the and in of the of the bound water in the The mutation the S. and J. K. The structures of various proton and chloride pumps and MastR structures the importance of the in the It that the side in HRs the Schiff base water from the Schiff their conversion to proton pumps. It is to that be for the conversion of pump an to convert to a proton (10Muroda K. Nakashima K. Shibata M. Demura M. Kandori H. Protein-bound water as the determinant of asymmetric functional conversion between light-driven proton and chloride pumps.Biochemistry. 2012; 51 (22583333): 4677-468410.1021/bi300485rCrossref PubMed Scopus (40) Google with to conservation and the functional proton be at the fine-tuning to changes and proton in the an pump study proton, and pumps K. Nomura Y. Kandori H. Asymmetric functional conversion of eubacterial light-driven ion pumps.J. Biol. Chem. 2016; 291 (26929409): 9883-989310.1074/jbc.M116.716498Abstract Full Full PubMed Scopus Google the of asymmetric functional conversion in which conversion mutation the amino acid changes in the motif. of the chloride pump into a proton pump and the proton pump of the the mutation outside the in It has been that MastR from a proton pump Demura M. of a cyanobacterial chloride-pumping rhodopsin and its conversion into a proton Biol. Chem. 2016; 291 Full Full PubMed Scopus Google Scholar, M. J. Brown L.S. of the unique of chloride transport by a cyanobacterial Chem. Chem. 2018; PubMed Google Scholar). The structural of MastR to BR and the conservation of key functional (Fig. why for the of an proton pump. The crystal structures of MastR and MastR-T74D into the ion transport pathway and the of this group of chloride ion pumps with TSD motif. MastR resembles and most from an archaeal proton why the mutation functional conversion from to pump. The distinct a bound water molecule between the and is a for the the of proton which is by a of the the be to study MastR photocycle to the proton and of the ion transport of photocycle M. J. Brown L.S. of the unique of chloride transport by a cyanobacterial Chem. Chem. 2018; PubMed Google (Fig. and in this chloride pump be for crystal P. E.F. The 2018; PubMed Scopus Google Scholar, J.L. O. S. H. P. I. S. O.P. at 2019; PubMed Scopus Google Scholar).

Topics & Concepts