Evidence that halogenated furanones from Delisea pulchra inhibit acylated homoserine lactone (AHL)-mediated gene expression by displacing the AHL signal from its receptor protein.
Acylated homoserine lactone (AHL)-mediated gene expression controls phenotypes involved in colonization, often specifically of higher organisms, in both marine and terrestrial environments. The marine red alga Delisea pulchra produces halogenated furanones which resemble AHLs structurally and show inhibitory activity at ecologically realistic concentrations in AHL bioassays. Evidence is presented that halogenated furanones displace tritiated OHHL [N-3-(oxohexanoyl)-L-homoserine lactone] from Escherichia coli cells overproducing LuxR with potencies corresponding to their respective inhibitory activities in an AHL-regulated bioluminescence assay, indicating that this is the mechanism by which furanones inhibit AHL-dependent phenotypes. Alternative mechanisms for this phenomenon are also addressed. General metabolic disruption was assessed with two-dimensional PAGE, revealing limited non-AHL-related effects. A direct chemical interaction between the algal compounds and AHLs, as monitored by 1H NMR spectroscopy, was shown not to occur in vitro. These results support the contention that furanones, at the concentrations produced by the alga, can control bacterial colonization of surfaces by specifically interfering with AHL-mediated gene expression at the level of the LuxR protein. (+info)
A group of alpha-1,4-glucan lyases and their genes from the red alga Gracilariopsis lemaneiformis: purification, cloning, and heterologous expression.
We present here the first report of a group of alpha-1,4-glucan lyases (EC 18.104.22.168) and their genes. The lyases produce 1, 5-anhydro-D-fructose from starch and related oligomers and polymers. The enzymes were isolated from the red alga Gracilariopsis lemaneiformis from the Pacific coasts of China and USA, and the Atlantic Coast of Venezuela. Three lyase isozymes (GLq1, GLq2 and GLq3) from the Chinese subspecies, two lyase isozymes (GLs1 and GLs2) from the USA subspecies and one lyase (GLa1) from the Venezuelan subspecies were identified and investigated. GLq1, GLq3, GLs1 and GLa1 were purified and partially sequenced. Based on the amino acid sequences obtained, three lyase genes or their cDNAs (GLq1, GLq2 and GLs1) were cloned and completely sequenced and two other genes (GLq3 and GLs2) were partially sequenced. The coding sequences of the lyase genes GLq1, GLq2 and GLs1 are 3267, 3276 and 3279 bp, encoding lyases of 1088, 1091 and 1092 amino acids, respectively. The deduced molecular masses of the mature lyases from the coding sequences are 117030, 117667 and 117790 Da, respectively, close to those determined by mass spectrometry using purified lyases. The amino acid sequence identity is more than 70% among the six algal lyase isozymes. The algal GLq1 gene was expressed in Pichia pastoris and Aspergillus niger, and the expression product was identical to the wild-type enzyme. (+info)
Crystal structure of C-phycocyanin from Cyanidium caldarium provides a new perspective on phycobilisome assembly.
The crystal structure of the light-harvesting protein phycocyanin from the cyanobacterium Cyanidium caldarium with novel crystal packing has been solved at 1.65-A resolution. The structure has been refined to an R value of 18.3% with excellent backbone and side-chain stereochemical parameters. In crystals of phycocyanin used in this study, the hexamers are offset rather than aligned as in other phycocyanins that have been crystallized to date. Analysis of this crystal's unique packing leads to a proposal for phycobilisome assembly in vivo and for a more prominent role for chromophore beta-155. This new role assigned to chromophore beta-155 in phycocyanin sheds light on the numerical relationships among and function of external chromophores found in phycoerythrins and phycoerythrocyanins. (+info)
Crystal structure of allophycocyanin from red algae Porphyra yezoensis at 2.2-A resolution.
The crystal structure of allophycocyanin from red algae Porphyra yezoensis (APC-PY) at 2.2-A resolution has been determined by the molecular replacement method. The crystal belongs to space group R32 with cell parameters a = b = 105.3 A, c = 189.4 A, alpha = beta = 90 degrees, gamma = 120 degrees. After several cycles of refinement using program X-PLOR and model building based on the electron density map, the crystallographic R-factor converged to 19.3% (R-free factor is 26.9%) in the range of 10.0 to 2.2 A. The r.m.s. deviations of bond length and angles are 0.015 A and 2.9 degrees, respectively. In the crystal, two APC-PY trimers associate face to face into a hexamer. The assembly of two trimers within the hexamer is similar to that of C-phycocyanin (C-PC) and R-phycoerythrin (R-PE) hexamers, but the assembly tightness of the two trimers to the hexamer is not so high as that in C-PC and R-PE hexamers. The chromophore-protein interactions and possible pathway of energy transfer were discussed. Phycocyanobilin 1alpha84 of APC-PY forms 5 hydrogen bonds with 3 residues in subunit 2beta of another monomer. In R-PE and C-PC, chromophore 1alpha84 only forms 1 hydrogen bond with 2beta77 residue in subunit 2beta. This result may support and explain great spectrum difference exists between APC trimer and monomer. (+info)
alpha-1,4-glucan lyases producing 1,5-anhydro-D-fructose from starch and glycogen have sequence similarity to alpha-glucosidases.
In the past few years a novel enzyme alpha-1,4-glucan lyase (EC 4.2. 2.13), which releases 1,5-anhydrofructose from starch and glycogen, has been cloned and characterized from red algae and fungi. Accumulated evidence indicates that the lytic degradation of starch and glycogen also occurs in other organisms. The present review focuses on the biochemical and molecular aspects of eight known alpha-1,4-glucan lyases and their genes from red algae and fungi. While the amino acid sequence identity is 75-80% among the alpha-1, 4-glucan lyases from each of the taxonomic groups, the identity between the algal and fungal alpha-1,4-glucan lyases is only 25-28%. Notably database searches disclosed that the alpha-1,4-glucan lyases have a clear identity of 23-28% with alpha-glucosidases of glycoside hydrolase family 31, thus for the first time linking enzymes from the class of hydrolases with that of lyases. The alignment of lyases and alpha-glucosidases revealed seven well-conserved regions, three of which have been reported to be involved in catalysis and substrate binding in alpha-glucosidases. The shared substrate and inhibitor specificity and sequence similarity of alpha-1,4-glucan lyases with alpha-glucosidases suggest that related structural elements are involved in the two different catalytic mechanisms. (+info)
Salicylhydroxamic acid inhibits delta6 desaturation in the microalga Porphyridium cruentum.
Treatment of the microalga Porphyridium cruentum with salicylhydroxamic acid (SHAM) inhibited growth and affected fatty acid composition. At a relatively low concentration (40 microM) SHAM predominantly inhibits Delta6 desaturation. The effect of the inhibitor was most intense in phosphatidylcholine (PC) and phosphatidylethanolamine, in which the proportions of the downstream products of the Delta6 desaturase were reduced, whereas that of the substrate, 18:2, increased. As a result of the availability of 18:2, 18:3omega3, which under normal conditions is not observed, appeared predominantly in chloroplastic lipids. Pulse labeling with linoleic acid has shown that SHAM inhibits Delta6 desaturation almost immediately, suggesting an apparent inhibition of the activity of the desaturase, rather than its synthesis or that of its cofactors. Furthermore, the addition of gamma-linolenic acid to SHAM-inhibited cultures relieved the inhibition. Following exposure to the inhibitor, 18:3omega3 appeared first in chloroplastic glycolipids and only later in PC, indicating that the former are the substrates for the first dedicated step of the proposed omega3 pathway in this alga. (+info)
Molecular structure, localization and function of biliproteins in the chlorophyll a/d containing oxygenic photosynthetic prokaryote Acaryochloris marina.
We investigated the localization, structure and function of the biliproteins of the oxygenic photosynthetic prokaryote Acaryochloris marina, the sole organism known to date that contains chlorophyll d as the predominant photosynthetic pigment. The biliproteins were isolated by means of sucrose gradient centrifugation, ion exchange and gel filtration chromatography. Up to six biliprotein subunits in a molecular mass range of 15.5-18.4 kDa were found that cross-reacted with antibodies raised against phycocyanin or allophycocyanin from a red alga. N-Terminal sequences of the alpha- and beta-subunits of phycocyanin showed high homogeneity to those of cyanobacteria and red algae, but not to those of cryptomonads. As shown by electron microscopy, the native biliprotein aggregates are organized as rod-shaped structures and located on the cytoplasmic side of the thylakoid membranes predominantly in unstacked thylakoid regions. Biochemical and spectroscopic analysis revealed that they consist of four hexameric units, some of which are composed of phycocyanin alone, others of phycocyanin together with allophycocyanin. Spectroscopic analysis of isolated photosynthetic reaction center complexes demonstrated that the biliproteins are physically attached to the photosystem II complexes, transferring light energy to the photosystem II reaction center chlorophyll d with high efficiency. (+info)
The secondary endosymbiont of the cryptomonad Guillardia theta contains alpha-, beta-, and gamma-tubulin genes.
Cryptomonads have acquired photosynthesis through secondary endosymbiosis: they have engulfed and retained a photosynthetic eukaryote. The remnants of this autotrophic symbiont are severely reduced, but a small volume of cytoplasm surrounding the plastid persists, along with a residual nucleus (the nucleomorph) that encodes only a few hundred genes. We characterized tubulin genes from the cryptomonad Guillardia theta. Despite the apparent absence of microtubules in the endosymbiont, we recovered genes encoding alpha-, beta-, and gamma-tubulins from the nucleomorph genome of G. theta. The presence of tubulin genes in the nucleomorph indicates that some component of the cytoskeleton is still present in the cryptomonad symbiont despite the fact that very little cytoplasm remains, no mitosis is known in the nucleomorph, and microtubules have never been observed anywhere in the symbiont. Phylogenetic analyses with nucleomorph alpha- and beta-tubulins support the origin of the cryptomonad nucleomorph from a red alga. We also characterized alpha and beta-tubulins from the host nucleus of G. theta and compared these with tubulins we isolated from two flagellates, Goniomonas truncata and Cyanophora paradoxa, previously proposed to be related to the cryptomonad host. Phylogenetic analyses support a relationship between the cryptomonad host and Goniomonas but do not support any relationship between cryptomonads and Cyanophora. (+info)