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Query: UMLS:C1832526 (PCC)
 5,967 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

High-resolution structures of the ligand binding core of GluR0, a glutamate receptor ion channel from Synechocystis PCC 6803, have been solved by X-ray diffraction. The GluR0 structures reveal homology with bacterial periplasmic binding proteins and the rat GluR2 AMPA subtype neurotransmitter receptor. The ligand binding site is formed by a cleft between two globular alpha/beta domains. L-Glutamate binds in an extended conformation, similar to that observed for glutamine binding protein (GlnBP). However, the L-glutamate gamma-carboxyl group interacts exclusively with Asn51 in domain 1, different from the interactions of ligand with domain 2 residues observed for GluR2 and GlnBP. To address how neutral amino acids activate GluR0 gating we solved the structure of the binding site complex with L-serine. This revealed solvent molecules acting as surrogate ligand atoms, such that the serine OH group makes solvent-mediated hydrogen bonds with Asn51. The structure of a ligand-free, closed-cleft conformation revealed an extensive hydrogen bond network mediated by solvent molecules. Equilibrium centrifugation analysis revealed dimerization of the GluR0 ligand binding core with a dissociation constant of 0.8 microM. In the crystal, a symmetrical dimer involving residues in domain 1 occurs along a crystallographic 2-fold axis and suggests that tetrameric glutamate receptor ion channels are assembled from dimers of dimers. We propose that ligand-induced conformational changes cause the ion channel to open as a result of an increase in domain 2 separation relative to the dimer interface.
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PMID:Mechanisms for ligand binding to GluR0 ion channels: crystal structures of the glutamate and serine complexes and a closed apo state. 1151 33

Two new depsipeptides have been isolated from a Symploca sp. collected in Palau. The gross structures of tasipeptins A (1) and B (2) were determined by standard spectroscopic techniques, and the absolute configuration of the amino acid units was determined by chiral HPLC. The relative stereochemistry of the 3-amino-6-hydroxy-2-piperidone (Ahp) moiety in both structures was determined by analysis of (2,3)J(H,H) values. Oxidation with PCC and acid hydrolysis unmasked this latent glutamic acid moiety, allowing for elucidation of the total configuration of 1 and 2. Tasipeptins A (1) and B (2) were cytotoxic toward KB cells with IC(50) values of 0.93 and 0.82 microM, respectively.
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PMID:Tasipeptins A and B: new cytotoxic depsipeptides from the marine cyanobacterium Symploca sp. 1276 94

The reversible red and far-red light-induced transitions of cyanobacterial phytochrome Cph1 from Synechocystis PCC 6803 were investigated by Fourier transform infrared (FTIR) difference spectroscopy. High-quality light-induced Pfr-Pr difference FTIR spectra were recorded for the 58 kDa N-terminal domain of Cph1 by repetitive photochemical cycling and signal averaging. The Pfr-Pr difference spectra in H(2)O and D(2)O were very similar to those previously reported for full-length 85 kDa Cph1.(1) Published assignments were extended by analysis of the effects of (13)C and (15)N isotope substitutions at selected sites in the phycocyanobilin chromophore and by (15)N global labeling of the protein. The Pfr-Pr difference spectra were dominated by an amide I peak/trough at 1653 cm(-1)(+)/1631 cm(-1)(-) and a smaller amide II band at 1554 cm(-1). Labeling effects allowed specific chromophore assignments for the C(1)=O (1736 cm(-1)(-)/1724 cm(-1)(+)) and C(19)=O (1704 cm(-1)(-)) carbonyl vibrations, C=C vibrations at 1589 cm(-1)(+), and bands at 1537(-), 1512(+), 1491(-), 1163(+), 1151(-), 1134(+), 1109(-), and 1072(-) cm(-1) that must involve chromophore C-N bonds. A variety of additional changes were insensitive to isotope labeling of the chromophore. Effects of (15)N labeling of the protein were used to tentatively assign some of these to specific amino acid changes. Those insensitive to (15)N labeling included a protonated aspartic or glutamic acid at 1734 cm(-1)(-)/1722 cm(-1)(+) and a cysteine at 2575 cm(-1)(+)/2557 cm(-1)(-). Bands sensitive to (15)N protein labeling at 1487 cm(-1)(+)/1502 cm(-1)(-) might arise from trytophan and bands at 1261 cm(-1)(+)/1244 cm(-1)(-) and 1107 cm(-1)(-)/1095 cm(-1)(+) might arise from a histidine environment or protonation change. These assignments are discussed in light of the 15Z-E photoisomerization model of phototransformation and the associated protein conformational changes.
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PMID:Assignments of the Pfr-Pr FTIR difference spectrum of cyanobacterial phytochrome Cph1 using 15N and 13C isotopically labeled phycocyanobilin chromophore. 1685 66

We constructed a mutant (CP43-Glu354Gln) of the cyanobacterium Synechocystis sp. PCC 6803 in which the glutamic acid at position 354 of the 43 kDa chlorophyll protein (CP43) was replaced with glutamine. To determine the effect of this mutation on the reaction processes of the Mn cluster in the oxygen-evolving complex, we mainly analyzed the spectroscopic properties, including Fourier transform infrared (FTIR) spectroscopy, of photosystem II core complexes. Mutant cells exhibited a lower oxygen-evolving activity than wild-type cells, and an altered pattern of flash-dependent delayed luminescence. This phenotype differed somewhat from an earlier report of the same mutant [Strickler, M. A., et al. (2008) Philos. Trans. R. Soc. London, Ser. B 363, 1179-1187]. FTIR difference spectroscopy revealed that CP43-Glu354 functions as a ligand to the Mn cluster, most likely with bridging bidentate coordination to two Mn ions in the S(1) state and chelating bidentate coordination to a single Mn ion in the S(2) state. A single water molecule was bound to the same Mn atom to which CP43-Glu354 was ligated, and this Mn atom was oxidized in the S(1)-to-S(2) transition. This is the first report on a binding site of a water molecule relevant to a specific amino acid ligand. We found that the Mn ion or ligand that is oxidized in the S(2)-to-S(3) transition was not directly coupled to CP43-Glu354. While the definitive assignment of ligation to the Mn atoms is still under debate, our identification of a novel water binding site will lead to new insights into the oxygen evolution mechanism.
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PMID:Effect of a single-amino acid substitution of the 43 kDa chlorophyll protein on the oxygen-evolving reaction of the cyanobacterium Synechocystis sp. PCC 6803: analysis of the Glu354Gln mutation. 1946 96

The initial steps of oxygenic photosynthetic electron transfer occur within photosystem II, an intricate pigment/protein transmembrane complex. Light-driven electron transfer occurs within a multistep pathway that is efficiently insulated from competing electron transfer pathways. The heart of the electron transfer system, composed of six linearly coupled redox active cofactors that enable electron transfer from water to the secondary quinone acceptor Q(B), is mainly embedded within two proteins called D1 and D2. We have identified a site in silico, poised in the vicinity of the Q(A) intermediate quinone acceptor, which could serve as a potential binding site for redox active proteins. Here we show that modification of Lysine 238 of the D1 protein to glutamic acid (Glu) in the cyanobacterium Synechocystis sp. PCC 6803, results in a strain that grows photautotrophically. The Glu thylakoid membranes are able to perform light-dependent reduction of exogenous cytochrome c with water as the electron donor. Cytochrome c photoreduction by the Glu mutant was also shown to significantly protect the D1 protein from photodamage when isolated thylakoid membranes were illuminated. We have therefore engineered a novel electron transfer pathway from water to a soluble protein electron carrier without harming the normal function of photosystem II.
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PMID:Engineering of an alternative electron transfer path in photosystem II. 2045 33

Taurine, the most abundant free amino acid in mammals, with many critical roles such as neuronal development, had so far only been reported to be synthetized in eukaryotes. Taurine is the major product of cysteine metabolism in mammals, and its biosynthetic pathway consists of cysteine dioxygenase and cysteine sulfinic acid decarboxylase (hCSAD). Sequence, structural, and mutational analyses of the structurally and sequentially related hCSAD and human glutamic acid decarboxylase (hGAD) enzymes revealed a three residue substrate recognition motif (X1aa19X2aaX3), within the active site that is responsible for coordinating their respective preferred amino acid substrates. Introduction of the cysteine sulfinic acid (CSA) motif into hGAD (hGAD-S192F/N212S/F214Y) resulted in an enzyme with a >700 fold switch in selectivity toward the decarboxylation of CSA over its preferred substrate, l-glutamic acid. Surprisingly, we found this CSA recognition motif in the genome sequences of several marine bacteria, prompting us to evaluate the catalytic properties of bacterial amino acid decarboxylases that were predicted by sequence motif to decarboxylate CSA but had been annotated as GAD enzymes. We show that CSAD from Synechococcus sp. PCC 7335 specifically decarboxylated CSA and that the bacteria accumulated intracellular taurine. The fact that CSAD homologues exist in certain bacteria and are frequently found in operons containing the recently discovered bacterial cysteine dioxygenases that oxidize l-cysteine to CSA supports the idea that a bona fide bacterial taurine biosynthetic pathway exists in prokaryotes.
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PMID:Discovery of a substrate selectivity motif in amino acid decarboxylases unveils a taurine biosynthesis pathway in prokaryotes. 2397 67

The conversion of solar energy (SEC) to storable chemical energy by photosynthesis has been performed by photosynthetic organisms, including oxygenic cyanobacteria for over 3 billion years. We have previously shown that crude thylakoid membranes from the cyanobacterium Synechocytis sp. PCC 6803 can reduce the electron transfer (ET) protein cytochrome c even in the presence of the PSII inhibitor DCMU. Mutation of lysine 238 of the Photosystem II D1 protein to glutamic acid increased the cytochrome reduction rates, indicating the possible position of this unknown ET pathway. In this contribution, we show that D1-K238E is rather unique, as other mutations to K238, or to other residues in the same vicinity, are not as successful in cytochrome c reduction. This observation indicates the sensitivity of ET reactions to minor changes. As the next step in obtaining useful SEC from biological material, we describe the use of crude Synechocystis membranes in a bio-photovoltaic cell containing an N-acetyl cysteine-modified gold electrode. We show the production of significant current for prolonged time durations, in the presence of DCMU. Surprisingly, the presence of cytochrome c was not found to be necessary for ET to the bio-voltaic cell.
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PMID:The Photosystem II D1-K238E mutation enhances electrical current production using cyanobacterial thylakoid membranes in a bio-photoelectrochemical cell. 2558 57


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