Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C1832526 (PCC)
 5,967 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A response regulator, NblR, of the cyanobacterium Synechococcus elongatus PCC 7942 is known to induce expression of the nblA gene, a key factor in phycobilisome degradation (bleaching) under nutrient-deprivation conditions. In this study, we observed phosphorylation-independent regulation of NblR activity. We constructed a mutant strain expressing NblR (D57A), in which a putative phospho-accepting Asp-57 was replaced with Ala residue. Under nitrogen deprivation, this strain exhibited the typical bleaching phenotype observed in wild-type cells. Moreover, in the mutant, the nblA transcript accumulated at a level similar to that of the wild type. Our results indicate that activation of NblR is independent of phosphorylation, if any, by a cognate histidine kinase. Screening of proteins interacting with NblR by yeast two-hybrid analysis revealed two candidates, MreC and NarB, suggesting a novel mechanism that activates NblR, or other functions of the response regulator.
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PMID:NblR is a novel one-component response regulator in the cyanobacterium Synechococcus elongatus PCC 7942. 1839 40

Cyanobacteria respond to environmental stress conditions by adjusting their photosynthesis machinery. In Synechococcus sp. PCC 7942, phycobilisome degradation and other acclimation responses after nutrient or high-light stress require activation by the orphan response regulator NblR, a member of the OmpR/PhoB family. Although NblR contains a putative phosphorylatable residue (Asp57), it lacks other conserved residues required to chelate the Mg(2+) necessary for aspartic acid phosphorylation or to transduce the phosphorylation signal. In close agreement with these features, NblR was not phosphorylated in vitro by the low-molecular-mass phosphate donor acetyl phosphate and mutation of Asp57 to Ala had no impact on previously characterized NblR functions in Synechococcus. On the other hand, in vitro and in vivo assays show that the default state of NblR is monomeric, suggesting that, despite input differences, NblR activation could involve the same general mechanism of activation by dimerization present in known members of the OmpR/PhoB family. Structural and functional data indicate that the receiver domain of NblR shares similarities with other phosphorylation-independent response regulators such as FrzS and HP1043. To acknowledge the peculiarities of these atypical 'two-component' regulators with phosphorylation-independent signal transduction mechanisms, we propose the term PIARR, standing for phosphorylation-independent activation of response regulator.
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PMID:Phosphorylation-independent activation of the atypical response regulator NblR. 1883 6

The PsbL protein is one of three low-molecular-weight subunits identified at the monomer-monomer interface of photosystem II (PSII) [Ferreira et al. (2004) Science 303:1831-1838; Loll et al. (2005) Nature 438:1040-1044]. We have employed site-directed mutagenesis to investigate the role of PsbL in Synechocystis sp. PCC 6803 cells. Truncation of the C-terminus by deleting the last four residues (Tyr-Phe-Phe-Asn) prevented association of PsbL with the CP43-less monomeric sub-complex and therefore blocked PSII assembly resulting in an obligate photoheterotrophic strain. Replacement of these residues with Ala created four photoautotrophic mutants. Compared to wild type, the F37A, F38A, and N39A strains had reduced levels of assembled PSII centers and F37A and F38A cells were readily photodamaged. In contrast, Y36A and Y36F mutants were similar to wild type. However, each of these strains had elevated levels of the CP43-less inactive monomeric complex. Mutations targeting a putative hydrogen bond between Arg-16 and sulfoquinovosyldiacylglycerol resulted in mutants that were also highly susceptible to photodamage. Similarly mutations targeting a conserved Tyr residue (Tyr-20) also destabilized PSII under high light and suggest that Tyr-20-lipid interactions or interactions of Tyr-20 with PsbT influence the ability of PSII to recover from photodamage.
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PMID:Directed mutagenesis of the transmembrane domain of the PsbL subunit of photosystem II in Synechocystis sp. PCC 6803. 1895 69

Synechocystis sp. PCC 6803 hemoglobin is a cyanobacterial Group I truncated hemoglobin. In the absence of an exogenous ligand, its single heme group is coordinated by His46 (E10, distal) and His70 (F8, proximal). The protein can undergo a post-translational modification by which His117 (H16, in the C-terminal helix) reacts with the heme 2-vinyl group to form a Markownikoff adduct. The new C-N bond prevents heme loss, alters the dynamics of the protein, and influences ligand binding to the heme group. To explore the factors conditioning the formation of the cross-link, variants of the protein that contained an alanine or a leucine at position 46 (E10) were prepared. A double replacement (His46Leu and Tyr22 (B10) to Phe) was also performed to perturb the network of interactions stabilizing bound exogenous ligand. The single and double replacements affected the optical and NMR properties of the globin, each in a different fashion. Heme-protein cross-linking, as promoted by sodium dithionite, was retarded by the replacement of His46, but reactivity was recovered when imidazole or cyanide was used as exogenous ligand. In addition, a significant amount of a second product was systematically obtained when dithionite treatment was performed on the cyanide-bound proteins. This species was identified by NMR spectroscopy to be an adduct to the 4-vinyl group. It was concluded that the specificity and rate of the cross-linking reaction depended critically on the nature of the sixth ligand to the heme iron.
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PMID:The role of the heme distal ligand in the post-translational modification of Synechocystis hemoglobin. 1899 44

Pex, a clock-related protein involved in the input pathway of the cyanobacterial circadian clock system, suppresses the expression of clock gene kaiA and lengthens the circadian period. Here, we determined the crystal structure of Anabaena Pex (AnaPex; Anabaena sp. strain PCC 7120) and Synechococcus Pex (SynPex; Synechococcus sp. strain PCC 7942). Pex is a homodimer that forms a winged-helix structure. Using the DNase I protection and electrophoresis mobility shift assays on a Synechococcus kaiA upstream region, we identified a minimal 25-bp sequence that contained an imperfectly inverted repeat sequence as the Pex-binding sequence. Based on crystal structure, we predicted the amino acid residues essential for Pex's DNA-binding activity and examined the effects of various Ala-substitutions in the alpha3 helix and wing region of Pex on in vitro DNA-binding activity and in vivo rhythm functions. Mutant AnaPex proteins carrying a substitution in the wing region displayed no specific DNA-binding activity, whereas those carrying a substitution in the alpha3 helix did display specific binding activity. But the latter were less thermostable than wild-type AnaPex and their in vitro functions were defective. We concluded that Pex binds a kaiA upstream DNA sequence via its wing region and that its alpha3 helix is probably important to its stability.
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PMID:Functionally important structural elements of the cyanobacterial clock-related protein Pex. 1903 44

In Synechocystis sp. PCC 6803 the histidine kinase SphS (sll0337) is involved in transcriptional activation of the phosphate (Pi)-acquisition system which includes alkaline phosphatase (AP). The N-terminal region of SphS contains both a hydrophobic region and a Per-Arnt-Sim (PAS) domain. The C-terminal region has a highly conserved transmitter domain. Immunological localization studies on heterologously expressed SphS in Escherichia coli indicate that the hydrophobic region is important for membrane localization. In order to evaluate the function of the N-terminal region of SphS, deletion mutants under the control of the native promoter were analysed for in vivo AP activity. Deletion of the N-terminal hydrophobic region resulted in loss of AP activity under both Pi-deficient and Pi-sufficient conditions. Substitution of the hydrophobic region of SphS with that from the Ni2+-sensing histidine kinase, NrsS, resulted in the same induction characteristics as SphS. Deletion of the PAS domain resulted in the constitutive induction of AP activity regardless of Pi availability. To characterize the PAS domain in more in detail, four amino acid residues conserved in the PAS domain were substituted with Ala. Among the mutants R121A constitutively expressed AP activity, suggesting that R121 is important for the function of the PAS domain. Our observations indicated that the presence of a transmembrane helix in the N-terminal region of SphS is critical for activity and that the PAS domain is involved in perception of Pi availability.
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PMID:Function of the N-terminal region of the phosphate-sensing histidine kinase, SphS, in Synechocystis sp. PCC 6803. 1938 60

The structure of the reduced form of cytochrome c(6) from the mesophilic cyanobacterium Synechococcus sp. PCC 7002 has been determined at 1.2 A and refined to an R-factor of 0.107. This protein is unique among all known cytochromes c(6), owing to the presence of an unusual seven-residue insertion, KDGSKSL(44-50), which differs from the insertion found in the recently discovered plant cytochromes c(6A). Furthermore, the present protein is unusual because of its very high content (36%) of the smallest residues (glycine and alanine). The structure reveals that the overall fold of the protein is similar to that of other class I c-type cytochromes, despite the presence of the specific insertion. The insertion is located within the most variable region of the cytochrome c(6) sequence, i.e. between helices II and III. The first six residues [KDGSKS(44-49)] form a loop, whereas the last residue, Leu50, extends the N-terminal beginning of helix III. Several specific noncovalent interactions are found inside the insertion, as well as between the insertion and the rest of the protein. The crystal structure contains three copies of the cytochrome c(6) molecule per asymmetric unit, and is characterized by an unusually high packing density, with solvent occupying barely 17.58% of the crystal volume.
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PMID:Atomic-resolution structure of reduced cyanobacterial cytochrome c6 with an unusual sequence insertion. 1967 39

Ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) is a globally significant biocatalyst that facilitates the removal and sequestration of CO2 from the biosphere. Rubisco-catalyzed CO2 reduction thus provides virtually all of the organic carbon utilized by living organisms. Despite catalyzing the rate-limiting step of photosynthetic and chemoautotrophic CO2 assimilation, Rubisco is markedly inefficient as the competition between O2 and CO2 for the same substrate limits the ability of aerobic organisms to obtain maximum amounts of organic carbon for CO2-dependent growth. Random and site-directed mutagenesis procedures were coupled with genetic selection to identify an "oxygen-insensitive" mutant cyanobacterial (Synechococcus sp. strain PCC 6301) Rubisco that allowed for CO2-dependent growth of a host bacterium at an oxygen concentration that inhibited growth of the host containing wild-type Synechococcus Rubisco. The mutant substitution, A375V, was identified as an intragenic suppressor of D103V, a negative mutant enzyme incapable of supporting autotrophic growth. Ala-375 (Ala-378 of spinach Rubisco) is a conserved residue in all form I (plant-like) Rubiscos. Structure-function analyses indicate that the A375V substitution decreased the enzyme's oxygen sensitivity (and not CO2/O2 specificity), possibly by rearranging a network of interactions in a fairly conserved hydrophobic pocket near the active site. These studies point to the potential of engineering plants and other significant aerobic organisms to fix CO2 unfettered by the presence of O2.
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PMID:A Rubisco mutant that confers growth under a normally "inhibitory" oxygen concentration. 1970 20

Stopped-flow absorption and isotope effect experiments have been used to dissect the mechanism of formation of the enzyme cysteinyl persulfide intermediate in the reaction of a cysteine desulfurase (CD), CD0387 from Synechocystis sp. strain PCC 6803. Seven accumulating intermediates have been identified and tentatively mapped onto the CD chemical mechanism originally proposed by Dean, White, and co-workers [Zheng, L., White, R. H., Cash, V. L., and Dean, D. R. (1994) Biochemistry 33, 4714-4720]. The first intermediate with lambda(max) approximately 350 nm is assigned as either a gem-diamine complex or a thiol adduct formed by nucleophilic attack of either the amine group or the sulfhydryl group of the substrate on the internal aldimine form of the pyridoxal 5'-phosphate (PLP) cofactor. The second intermediate, with absorption features at approximately 417 and approximately 340 nm, is assigned as Cys aldimine and Cys ketimine forms in rapid equilibrium. In agreement with this assignment, a significant substrate alpha-deuterium equilibrium isotope effect ((2)H-EIE) favoring the aldimine form (417 nm) is observed in the second state produced in either wild-type CD0387 or the inactive C326A variant protein, which lacks the nucleophilic cysteine residue and is thus unable to proceed beyond this state unless "rescued" by a high concentration of an exogenous thiol. The third intermediate has an additional approximately 506 nm feature, characteristic of a quinonoid form, along with the features of the previous state. Its assignment as Ala aldimine, quinonoid, and ketimine forms in rapid equilibrium, which associates its formation with C-S bond cleavage and persulfide formation, is supported by its failure to develop in the C326A variant and the normal kinetic isotope effect ((2)H-KIE) on its formation, which is similar in magnitude to the (2)H-EIE disfavoring Cys-ketimine (from which the third state forms) in the second state. Decay of the Ala quinonoid absorption is tentatively attributed to a conformational change by the enzyme that disfavors this form in its equilibrium with Ala aldimine and Ala ketimine. Subsequent decay of the ketimine absorption ( approximately 340 nm) is attributed to release of Ala from the cofactor with an observed rate constant of 10 s(-1), the slowest step in the persulfide-forming half-reaction. The enzyme-persulfide.Ala complex dissociates rapidly with a K(d) of 98 mM. The final state with lambda(max) approximately 350 nm is assigned as a dead-end complex between the enzyme-persulfide and a second l-cysteine, which adds to the cofactor via its sulfhydryl group, possibly forming a cyclic thiazolidine species.
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PMID:Kinetic analysis of cysteine desulfurase CD0387 from Synechocystis sp. PCC 6803: formation of the persulfide intermediate. 1988 76

Antiferromagnetically coupled Mn(III)Mn(IV) dimers have been commonly used to study biological systems that exhibit complex exchange interactions. Such is the case for the oxygen evolving complex (OEC) in photosystem II (PSII), where we have studied whether the C-terminal carboxylate of D1-Ala344 is directly bound to the Mn cluster. To probe these protein-derived carboxylate hyperfine interactions, which give direct bonding information, Q-band (34 GHz) Mims ENDOR was performed on a Mn(III)Mn(IV) dimer ([Mn(III)Mn(IV)(mu-O)(2)mu-OAc(TACN)(2)](BPh(4))(2)) (1) that was labeled with (13)C (I = (1)/(2)) at the carboxylate position of the acetate bridge. A(dip) is computed based on atomic coordinates from available X-ray crystal structures to be [-2.4, -0.8, 3.2] MHz. The value for A(iso) was determined based on simulation of the experimental ENDOR data, for complex 1 A(iso) = -1 MHz. Similar studies were then performed on PSII from Synechocystis sp. PCC 6803, in which all alanine-derived C=O groups are labeled with (13)C including the C-terminal alpha-COO(-) group of D1 (Ala344), as well as PSII proteins uniformly labeled with (13)C. Using recent X-ray crystallography data from T. elongatus the values for A(dip) were calculated and simulations of the experimental data led to A(iso) values of 1.2, 1, and 2 MHz, respectively. We infer from complex 1 that an A(iso) significantly larger than 1.2 MHz for a Mn-coordinating carboxylate moiety is unlikely. Therefore, we support the closer arrangement of Ala344 suggested by the Loll and Guskov structures and conclude that the C-terminal carboxylate of D1 polypeptide is directly bound to the Mn cluster.
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PMID:13C ENDOR reveals that the D1 polypeptide C-terminus is directly bound to Mn in the photosystem II oxygen evolving complex. 2003 96


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