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The primary structure of sensory rhodopsin II: a member of an additional retinal protein subgroup is coexpressed with its transducer, the halobacterial transducer of rhodopsin II.

ABSTRACT: The blue-light receptor genes (sopII) of sensory rhodopsin (SR) II were cloned from two species, the halophilic bacteria Haloarcula vallismortis (vSR-II) and Natronobacterium pharaonis (pSR-II). Upstream of both sopII gene loci, sequences corresponding to the halobacterial transducer of rhodopsin (Htr) II were recognized. In N. pharaonis, psopII and phtrII are transcribed as a single transcript. Comparison of the amino acid sequences of vHtr-II and pHtr-II with Htr-I and the chemotactic methyl-accepting proteins from Escherichia coli revealed considerable identities in the signal domain and methyl-accepting sites. Similarities with Htr-I in Halobacterium salinarium suggest a common principle in the phototaxis of extreme halophiles. Alignment of all known retinal protein sequences from Archaea identifies both SR-IIs as an additional subgroup of the family. Positions defining the retinal binding site are usually identical with the exception of Met-118 (numbering is according to the bacteriorhodopsin sequence), which might explain the typical blue color shift of SR-II to approximately 490 nm. In archaeal retinal proteins, the function can be deduced from amino acids in positions 85 and 96. Proton pumps are characterized by Asp-85 and Asp-96; chloride pumps by Thr-85 and Ala-96; and sensors by Asp-85 and Tyr-96 or Phe-96.

SUBMITTER: Seidel R

PROVIDER: S-EPMC42354 | biostudies-other | 1995 Mar

REPOSITORIES: biostudies-other

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The primary structure of sensory rhodopsin II: a member of an additional retinal protein subgroup is coexpressed with its transducer, the halobacterial transducer of rhodopsin II.

Seidel R R Scharf B B Gautel M M Kleine K K Oesterhelt D D Engelhard M M

Proceedings of the National Academy of Sciences of the United States of America 19950301 7

The blue-light receptor genes (sopII) of sensory rhodopsin (SR) II were cloned from two species, the halophilic bacteria Haloarcula vallismortis (vSR-II) and Natronobacterium pharaonis (pSR-II). Upstream of both sopII gene loci, sequences corresponding to the halobacterial transducer of rhodopsin (Htr) II were recognized. In N. pharaonis, psopII and phtrII are transcribed as a single transcript. Comparison of the amino acid sequences of vHtr-II and pHtr-II with Htr-I and the chemotactic methyl-a ...[more]

PMID: 7708770

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Project description:A methylated membrane protein of 97 kDa was suggested on the basis of mutant analysis to transduce signals from the phototaxis receptor sensory rhodopsin I to the flagellar motor in Halobacterium halobium. Here we report isolation of the proposed transducer protein, cloning of its gene based on partial protein sequences, the complete gene sequence, and analysis of the encoded primary structure. The 1611-base-pair gene termination codon overlaps the initiator ATG of the sopI gene, which encodes the sensory rhodopsin I apoprotein. The predicted size of 57 kDa for the methylated protein indicates an aberrant electrophoretic migration on SDS/polyacrylamide gels, as occurs with other acidic halophilic proteins. Putative promotor elements are located in an A+T-rich region upstream of the gene. Comparison of the translated nucleotide sequence with N-terminal sequence of the purified protein shows the protein is synthesized without a processed leader peptide and the N-terminal methionine is removed in the mature protein. The deduced protein sequence predicts two transmembrane helices near the N terminal that would anchor the protein to the membrane. Beyond this hydrophobic region of 46 residues, the remainder of the protein (536-amino acid residues total) is hydrophilic. The C-terminal 270 residues contain a region homologous to the signaling domains of eubacterial transducers (e.g., Escherichia coli Tsr protein), flanked by two regions homologous to the methylation domains of the transducer family. The protein differs from E. coli Tsr in that it does not have an extramembranous-receptor binding domain but instead has a more extended cytoplasmic region. Coexpression of the methyl-accepting protein gene (designated htrI) and sopI restores sensory rhodopsin I phototaxis to a mutant (Pho81) that contains a deletion in the htrI/sopI region. These results extend the eubacterial transducer family to the archaebacteria and substantiate the proposal that the methylated membrane protein functions as a signal-transducing relay between sensory rhodopsin I and cytoplasmic sensory-pathway components.

Project description:Recently, a large family of transducer proteins in the Archaeon Halobacterium salinarium was identified. On the basis of the comparison of the predicted structural domains of these transducers, three distinct subfamilies of transducers were proposed. Here we report isolation, complete gene sequences, and analysis of the encoded primary structures of transducer gene htrII, a member of family B, and its blue light receptor gene (sopII) of sensory rhodopsin II (SRII). The start codon ATG of the 714-bp sopII gene is one nucleotide beyond the termination codon TGA of the 2298-bp htrII gene. The deduced protein sequence of HtrII predicts a eubacterial chemotaxis transducer type with two hydrophobic membrane-spanning segments connecting sizable domains in the periplasm and cytoplasm. HtrII has a common feature with HtrI, the sensory rhodopsin I transducer; like HtrI, HtrII possesses a hydrophilic loop structure just after the second transmembrane segment. The C-terminal 299 residues (765 amino acid residues total) of HtrII show strong homology to the signaling and methylation domain of eubacterial transducer Tsr. The hydropathy plot of the primary structure of SRII indicates seven membrane-spanning alpha-helical segments, a characteristic feature of retinylidene proteins ("rhodopsins") from a widespread family of photoactive pigments. SRII shows high identity with SRI (42%), bacteriorhodopsin (BR) (32%), and halorhodopsin (24%). The crucial positions for retinal binding sites in these proteins are nearly identical, with the exception of Met-118 (numbering according to the mature BR sequence), which is replaced by Val in SRII. In BR, residues Asp-85 and Asp-96 are crucial in proton pumping. In SRII, the position corresponding to Asp-85 in BR is conserved, but the corresponding position of Asp-96 is replaced by an aromatic Tyr. Coexpression of the htrII and sopII genes restores SRII phototaxis to a mutant (Pho81) that contains a deletion in the htrI/sopI and insertion in htrII/sopII regions. This paper describes the first example that both HtrI and HtrII exist in the same halobacterial cell, confirming that different sensory rhodopsins SRI and SRII in the same organism have their own distinct transducers.

Dataset Information

The primary structure of sensory rhodopsin II: a member of an additional retinal protein subgroup is coexpressed with its transducer, the halobacterial transducer of rhodopsin II.

Publications

The primary structure of sensory rhodopsin II: a member of an additional retinal protein subgroup is coexpressed with its transducer, the halobacterial transducer of rhodopsin II.

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