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1.
Discovery of alkenones with variable methylene‐interrupted double bonds: implications for the biosynthetic pathway
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Alkenones (C37–C40) are highly specific biomarkers produced by certain haptophyte algae in ocean and lacustrine environments and have been widely used for paleoclimate studies. Unusual shorter‐chain alkenones (SCA; e.g., C35 and C36) have been found in environmental and culture samples, but the origin and structure of these compounds are much less understood. The marine alkenone producer, Emiliania huxleyi CCMP2758 strain, was reported with abundant C35:2Me (?12, 19) alkenones when cultured at 15°C (Prahl et al. 2006). Here we show, when this strain is cultured at 4°C–10°C, that CCMP2758 produces abundant C35:3Me, C36:3Me, and small amounts of C36:3Et alkenones with unusual double‐bond positions of ?7, 12, 19. We determine the double‐bond positions of the C35:3Me and C36:3Me alkenones by GC‐MS analysis of the dimethyl disulfide and cyclobutylamine derivatives, and we provide the first temperature calibrations based on the unsaturation ratios of the C35 and C36 alkenones. Previous studies have found C35:2Me (?14, 19) and C36:2Et (?14, 19) alkenones with three‐methylene interruption in the Black Sea sediments, but this is the first reported instance of alkenones with a mixed three‐ and five‐methylene interruption configuration in the double‐bond positions. The discovery of these alkenones allows us to propose a novel biosynthetic scheme, termed the SCA biosynthesis pathway, that simultaneously rationalizes the formation of both the C35:3Me (?7, 12, 19) alkenone in our culture and the ?14, 19 Black Sea type alkenones without invoking new desaturases for the unusual double‐bond positions. 相似文献
2.
A route of synthesis for the preparation of unsaturated pheromones is presented. It permits the synthesis of monounsaturated and diunsaturated compounds, with varying position and configuration of double bonds, by stereoselective carbonyl olefination. The choice of appropriate ω-functional aldehydes and phosphoranes makes possible the synthesis of (Z)-alkenols and alkenyl acetates with the double bond in any position desired. Bifunctional synthones are used in stereoselective Wittig reactions for the preparation of diunsaturated sex attractants. 相似文献
3.
《Bioscience, biotechnology, and biochemistry》2013,77(12):3174-3179
Δ12 and ω3 fatty acid desaturases are key enzymes in the synthesis of polyunsaturated fatty acids (PUFAs), which are important constituents of membrane glycerolipids and also precursors to signaling molecules in many organisms. In this study, we determined the substrate specificity and regioselectivity of the Δ12 and ω3 fatty acid desaturases from Saccharomyces kluyveri (Sk-FAD2 and Sk-FAD3). Based on heterologous expression in Saccharomyces cerevisiae, it was found that Sk-FAD2 converted C16–20 monounsaturated fatty acids to diunsaturated fatty acids by the introduction of a second double bond at the ν+3 position, while Sk-FAD3 recognized the ω3 position of C18 and C20. Furthermore, fatty acid analysis of major phospholipids suggested that Sk-FAD2 and Sk-FAD3 have no strong substrate specificity toward the lipid polar head group or the sn-positions of fatty acyl groups in phospholipids. 相似文献
4.
A thioesterase bypasses the requirement for exogenous fatty acids in the plsX deletion of Streptococcus pneumoniae
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Joshua B. Parsons Matthew W. Frank Marc J. Eleveld Joost Schalkwijk Tyler C. Broussard Marien I. de Jonge Charles O. Rock 《Molecular microbiology》2015,96(1):28-41
PlsX is an acyl‐acyl carrier protein (ACP):phosphate transacylase that interconverts the two acyl donors in Gram‐positive bacterial phospholipid synthesis. The deletion of plsX in Staphylococcus aureus results in a requirement for both exogenous fatty acids and de novo type II fatty acid biosynthesis. Deletion of plsX (SP0037) in Streptococcus pneumoniae did not result in an auxotrophic phenotype. The ΔplsX S. pneumoniae strain was refractory to myristic acid‐dependent growth arrest, and unlike the wild‐type strain, was susceptible to fatty acid synthesis inhibitors in the presence of exogenous oleate. The ΔplsX strain contained longer chain saturated fatty acids imparting a distinctly altered phospholipid molecular species profile. An elevated pool of 18‐ and 20‐carbon saturated fatty acids was detected in the ΔplsX strain. A S. pneumoniae thioesterase (TesS, SP1408) hydrolyzed acyl‐ACP in vitro, and the ΔtesS ΔplsX double knockout strain was a fatty acid auxotroph. Thus, the TesS thioesterase hydrolyzed the accumulating acyl‐ACP in the ΔplsX strain to liberate fatty acids that were activated by fatty acid kinase to bypass a requirement for extracellular fatty acid. This work identifies tesS as the gene responsible for the difference in exogenous fatty acid growth requirement of the ΔplsX strains of S. aureus and S. pneumoniae. 相似文献
5.
A ten gene‐containing genomic island determines flagellin glycosylation: implication for its regulatory role in motility and virulence of Xanthomonas oryzae pv. oryzae
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Chao Yu Huamin Chen Fang Tian Fenghuan Yang Xiaochen Yuan Ching‐Hong Yang Chenyang He 《Molecular Plant Pathology》2018,19(3):579-592
6.
ω‐Turn: A novel β‐turn mimic in globular proteins stabilized by main‐chain to side‐chain CH···O interaction
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Jesmita Dhar Pinak Chakrabarti Harpreet Saini Gajendra Pal Singh Raghava Raghuvansh Kishore 《Proteins》2015,83(2):203-214
Mimicry of structural motifs is a common feature in proteins. The 10‐membered hydrogen‐bonded ring involving the main‐chain C?O in a β‐turn can be formed using a side‐chain carbonyl group leading to Asx‐turn. We show that the N? H component of hydrogen bond can be replaced by a Cγ‐H group in the side chain, culminating in a nonconventional C? H···O interaction. Because of its shape this β‐turn mimic is designated as ω‐turn, which is found to occur ~three times per 100 residues. Three residues (i to i + 2) constitute the turn with the C? H···O interaction occurring between the terminal residues, constraining the torsion angles ?i + 1, ψi + 1, ?i + 2 and χ′1(i + 2) (using the interacting Cγ atom). Based on these angles there are two types of ω‐turns, each of which can be further divided into two groups. Cβ‐branched side‐chains, and Met and Gln have high propensities to occur at i + 2; for the last two residues the carbonyl oxygen may participate in an additional interaction involving the S and amino group, respectively. With Cys occupying the i + 1 position, such turns are found in the metal‐binding sites. N‐linked glycosylation occurs at the consensus pattern Asn‐Xaa‐Ser/Thr; with Thr at i + 2, the sequence can adopt the secondary structure of a ω‐turn, which may be the recognition site for protein modification. Location between two β‐strands is the most common occurrence in protein tertiary structure, and being generally exposed ω‐turn may constitute the antigenic determinant site. It is a stable scaffold and may be used in protein engineering and peptide design. Proteins 2015; 83:203–214. © 2014 Wiley Periodicals, Inc. 相似文献
7.
《Biochimica et Biophysica Acta (BBA)/Molecular and Cell Biology of Lipids》2019,1864(8):1134-1144
The interest in understanding the capacity of aquatic invertebrates to biosynthesise omega-3 (ω3) long-chain (≥C20) polyunsaturated fatty acids (LC-PUFA) has increased in recent years. Using the common octopus Octopus vulgaris as a model species, we previously characterised a ∆5 desaturase and two elongases (i.e. Elovl2/5 and Elovl4) involved in the biosynthesis of LC-PUFA in molluscs. The aim of this study was to characterise both molecularly and functionally, two methyl-end (or ωx) desaturases that have been long regarded to be absent in most animals. O. vulgaris possess two ωx desaturase genes encoding enzymes with ∆12 and ω3 regioselectivities enabling the de novo biosynthesis of the C18 PUFA 18:2ω6 (LA, linoleic acid) and 18:3ω3 (ALA, α-linolenic acid), generally regarded as dietary essential for animals. The O. vulgaris ∆12 desaturase (“ωx2”) mediates the conversion of 18:1ω9 (oleic acid) into LA, and subsequently, the ω3 desaturase (“ωx1”) catalyses the ∆15 desaturation from LA to ALA. Additionally, the O. vulgaris ω3 desaturase has ∆17 capacity towards a variety of C20 ω6 PUFA that are converted to their ω3 PUFA products. Particularly relevant was the affinity of the ω3 desaturase towards 20:4ω6 (ARA, arachidonic acid) to produce 20:5ω3 (EPA, eicosapentaenoic acid), as supported by yeast heterologous expression, and enzymatic activity exhibited in vivo when paralarvae were incubated in the presence of [1-14C]20:4ω6. These results confirmed that several routes enabling EPA biosynthesis are operative in O. vulgaris whereas ARA and docosahexaenoic acid (DHA, 22:6ω3) should be considered essential fatty acids since endogenous production appears to be limited. 相似文献
8.
Anacystis nidulans Richt., a unicellular cyanobacterium, can incorporate exogenously supplied fatty acids, including odd-numbered carbon fatty acid (OFAs), into the acylglycerols of cell membranes. Data are presented for the uptake of undecanoic acid (11:0) into cells of A. nidulans, the subsequent elongation up to C17, and incorporation of OFA into the four major membrane acylglycerols. The incorporation of OFAs was followed by desaturation of part of the saturated fatty acid to monoenoic fatty acid. Positional analyses of the double bonds of these manoenoic fatty acids suggest that there is one desaturase that inserts a Δ9 bond in both odd- and even-numbered fatty acids of varying chain length. Our data also suggest that there is no positional specificity for chain length on the glycerol backbone by the acyltransferases. 相似文献
9.
Nora Richter William M. Longo Sarabeth George Anna Shipunova Yongsong Huang Linda Amaral‐Zettler 《Geobiology》2019,17(3):272-280
Members of the order Isochrysidales are unique among haptophyte lineages in being the exclusive producers of alkenones, long‐chain ketones that are commonly used for paleotemperature reconstructions. Alkenone‐producing haptophytes are divided into three major groups based largely on molecular ecological data: Group I is found in freshwater lakes, Group II commonly occurs in brackish and coastal marine environments, and Group III consists of open ocean species. Each group has distinct alkenone distributions; however, only Groups II and III Isochrysidales currently have cultured representatives. The uncultured Group I Isochrysidales are distinguished geochemically by the presence of tri‐unsaturated alkenone isomers (C37:3b Me, C38:3b Et, C38:3b Me, C39:3b Et) present in water column and sediment samples, yet their genetic diversity, morphology, and environmental controls are largely unknown. Using small‐subunit (SSU) ribosomal RNA (rRNA) marker gene amplicon high‐throughput sequencing of environmental water column and sediment samples, we show that Group I is monophyletic with high phylogenetic diversity and contains a well‐supported clade separating the previously described “EV” clade from the “Greenland” clade. We infer the first partial large‐subunit (LSU) rRNA gene Group I sequence phylogeny, which uncovered additional well‐supported clades embedded within Group I. Relative to Group II, Group I revealed higher levels of genetic diversity despite conservation of alkenone signatures and a closer evolutionary relationship with Group III. In Group I, the presence of the tri‐unsaturated alkenone isomers appears to be conserved, which is not the case for Group II. This suggests differing environmental influences on Group I and II and perhaps uncovers evolutionary constraints on alkenone biosynthesis. 相似文献
10.
The desaturation of long-chain fatty acids is a ubiquitous biotransformation which plays a critical role in the biosynthesis of plant lipids. Species-specific variations lead to unusual fatty acid signatures. Of particular interest is the unique ability of desaturases to oxidize unactivated hydrocarbon chains in such a chemo-, regio- and stereoselective manner. As part of ongoing research into the structure/activity relationships of this large class of enzymes, useful mechanistic tools have been developed to probe the active site. Recently a combination of stereo- and regiospecific deuterium, sulfur and fluorine labelling has been used to study the mechanism of a soluble plant Δ9 desaturase. The study of several membrane-bound desaturases has led to the conclusion that the dehydrogenation (desaturation) process is initiated by a kinetically important hydrogen activation step at the carbon of the incipient double bond which is closest to the acyl terminus of the fatty acid chain. A detailed analysis of a related 1,4-desaturation process has also been carried out. 相似文献
11.
Mass spectral data of a phytosterolin and its tetraacetate from Trianthema pentandra show that sitosterol-d(+)-glucoside reported earlier1 was a mixture of sitosteroI-d(+)-glucoside and stigmasterol-d(+)-glucoside. The structure of a ketone has been suggested as nonacos-1-en-4-one, on the basis of physicochemical data. The positions of the double bond and the carbonyl group have been established by MS and NMR data. This is the first report in plants of a C29 ketone with a terminal double bond and carbonyl group at position 4. 相似文献
12.
The photosynthetic efficiency of the CO2‐concentrating mechanism in two forms of single‐cell C4 photosynthesis in the family Chenopodiaceae was characterized. The Bienertioid‐type single‐cell C4 uses peripheral and central cytoplasmic compartments (Bienertia sinuspersici), while the Borszczowioid single‐cell C4 uses distal and proximal compartments of the cell (Suaeda aralocaspica). C4 photosynthesis within a single‐cell raises questions about the efficiency of this type of CO2‐concentrating mechanism compared with the Kranz‐type. We used measurements of leaf CO2 isotope exchange (Δ13C) to compare the efficiency of the single‐cell and Kranz‐type forms of C4 photosynthesis under various temperature and light conditions. Comparisons were made between the single‐cell C4 and a sister Kranz form, S. eltonica[NAD malic enzyme (NAD ME) type], and with Flaveria bidentis[NADP malic enzyme (NADP‐ME) type with Kranz Atriplicoid anatomy]. There were similar levels of Δ13C discrimination and CO2 leakiness (?) in the single‐cell species compared with the Kranz‐type. Increasing leaf temperature (25 to 30 °C) and light intensity caused a decrease in Δ13C and ? across all C4 types. Notably, B. sinuspersici had higher Δ13C and ? than S. aralocaspica under lower light. These results demonstrate that rates of photosynthesis and efficiency of the CO2‐concentrating mechanisms in single‐cell C4 plants are similar to those in Kranz‐type. 相似文献
13.
A “crude plastid” preparation from young pea leaves converts linoleate [1-14C] or [U-14C] (ammonium salt or free acid) into a C12 dibasic acid with a double bond at Δ9. 相似文献
14.
A new pimarane diterpenoid, named botryopimarene A ( 1 ), was discovered from the fungus Botryotinia fuckeliana MCCC 3 A00494 isolated from the deep‐sea water, together with ten known compounds. The planar structure of 1 was established based on the extensive spectroscopic analyses. The absolute configurations of tricyclic system in 1 were resolved by the theoretical ECD calculation, while the 15,16‐diol moiety in the side chain was resolved by the Mo2(OAc)4‐induced ECD spectrum. Compound 1 , featuring a Δ9(11) double bond, was rarely discovered in pimarane family. Compounds 1 – 11 were tested for their cytotoxic activities using six human cancer cell lines by the MTT method. However, none of the compounds exhibited detectable cytotoxicities (IC50 >20 μm ). 相似文献
15.
Many macromolecular interactions, including protein‐nucleic acid interactions, are accompanied by a substantial negative heat capacity change, the molecular origins of which have generated substantial interest. We have shown previously that temperature‐dependent unstacking of the bases within oligo(dA) upon binding to the Escherichia coli SSB tetramer dominates the binding enthalpy, ΔHobs, and accounts for as much as a half of the observed heat capacity change, ΔCp. However, there is still a substantial ΔCp associated with SSB binding to ssDNA, such as oligo(dT), that does not undergo substantial base stacking. In an attempt to determine the origins of this heat capacity change, we have examined by isothermal titration calorimetry (ITC) the equilibrium binding of dT(pT)34 to SSB over a broad pH range (pH 5.0–10.0) at 0.02 M, 0.2 M NaCl and 1 M NaCl (25°C), and as a function of temperature at pH 8.1. A net protonation of the SSB protein occurs upon dT(pT)34 binding over this entire pH range, with contributions from at least three sets of protonation sites (pKa1 = 5.9–6.6, pKa2 = 8.2–8.4, and pKa3 = 10.2–10.3) and these protonation equilibria contribute substantially to the observed ΔH and ΔCp for the SSB‐dT(pT)34 interaction. The contribution of this coupled protonation (∼ −260 to −320 cal mol−1 K−1) accounts for as much as half of the total ΔCp. The values of the “intrinsic” ΔCp,0 range from −210 ± 33 cal mol−1 °K−1 to −237 ± 36 cal mol−1K−1, independent of [NaCl]. These results indicate that the coupling of a temperature‐dependent protonation equilibria to a macromolecular interaction can result in a large negative ΔCp, and this finding needs to be considered in interpretations of the molecular origins of heat capacity changes associated with ligand‐macromolecular interactions, as well as protein folding. Proteins 2000;Suppl 4:8–22. © 2000 Wiley‐Liss, Inc. 相似文献
16.
Lauren Davey Alejandro Cohen Jason LeBlanc Scott A. Halperin Song F. Lee 《Molecular microbiology》2016,99(2):236-253
Recently, we identified a novel disulfide oxidoreductase, SdbA, in the oral bacterium Streptococcus gordonii. Disulfide oxidoreductases form disulfide bonds in nascent proteins using a CXXC catalytic motif. Typically, the N‐terminal cysteine interacts with substrates, whereas the C‐terminal cysteine is buried and only reacts with the first cysteine of the motif. In this study, we investigated the SdbA C86P87D88C89 catalytic motif. In vitro, SdbA single cysteine variants at the N or C‐terminal position (SdbAC86P and SdbAC89A) were active but displayed different susceptibility to oxidation, and N‐terminal cysteine was prone to sulfenylation. In S. gordonii, mutants with a single N‐terminal cysteine were inactive and formed unstable disulfide adducts with other proteins. Activity was partially restored by inactivation of pyruvate oxidase, a hydrogen peroxide generator. Presence of the C‐terminal cysteine alone (in the SdbAC86P variant) could complement the ΔsdbA mutant and restore disulfide bond formation in recombinant and natural protein substrates. These results provide evidence that certain disulfide oxidoreductases can catalyze disulfide bond formation using a single cysteine of the CXXC motif, including the buried C‐terminal cysteine. 相似文献
17.
Biljana R. Deki Milenko N. Risti Marko Z. Mladenovi Vidoslav S. Deki Novica R. Risti Vladimir Ranelovi Niko S. Radulovi 《化学与生物多样性》2019,16(7)
Some carnation species (Dianthus spp., Caryophyllaceae) exhibit a strong resistance to drought stress that is connected with the increased surface wax formation. Wax composition is unknown for the majority of Dianthus spp. Herein, mass spectral and gas chromatographic data, in combination with synthesis and chemical transformations (transesterification and synthesis of dimethyl disulfide adducts), enabled the identification of 151 constituents of diethyl‐ether washings of fresh flowers of Dianthus cruentus Griseb . from Serbia. The flower wax contained, along with the dominant ubiquitous long‐chain n‐alkanes, homologous series of n‐ and branched (iso‐ and anteiso‐) long‐chain hexyl alkanoates/alkenoates and alkyl/alkenyl benzoates. The branching position in the mentioned hexyl esters was probed by synthesis of esters of three isomeric hexanols that were spectrally characterized (1H‐ and 13C‐NMR, IR, MS). The washings also contained long‐chain (Z)‐ and (E)‐alkenes (C23?C35) with several different double bond regiochemistries. Fifty‐five of these constituents (eight hexyl esters, two benzoates, and forty‐five alkenes) were detected for the first time in Plantae, while ten of these represent completely new compounds. The rare occurrence of these wax constituents makes them possible chemotaxonomic markers of this particular Dianthus sp. 相似文献
18.
William J. Pestle Mark Hubbe Erin K. Smith Joseph M. Stevenson 《American journal of physical anthropology》2015,157(4):694-703
Objective : Development of a model for the prediction of δ13Cprotein from δ13Ccollagen and Δ13Cap‐co. Model‐generated values could, in turn, serve as “consumer” inputs for multisource mixture modeling of paleodiet. Methods : Linear regression analysis of previously published controlled diet data facilitated the development of a mathematical model for predicting δ13Cprotein (and an experimentally generated error term) from isotopic data routinely generated during the analysis of osseous remains (δ13Cco and Δ13Cap‐co). Results : Regression analysis resulted in a two‐term linear model (δ13Cprotein (%) = (0.78 × δ13Cco) ? (0.58× Δ13Cap‐co) ? 4.7), possessing a high R‐value of 0.93 (r2 = 0.86, P < 0.01), and experimentally generated error terms of ±1.9% for any predicted individual value of δ13Cprotein. This model was tested using isotopic data from Formative Period individuals from northern Chile's Atacama Desert. Conclusions : The model presented here appears to hold significant potential for the prediction of the carbon isotope signature of dietary protein using only such data as is routinely generated in the course of stable isotope analysis of human osseous remains. These predicted values are ideal for use in multisource mixture modeling of dietary protein source contribution. Am J Phys Anthropol 157:694–703, 2015. © 2015 Wiley Periodicals, Inc. 相似文献
19.
20.
James R. Petrie Anne M. Mackenzie Pushkar Shrestha Qing Liu Dion F. Frampton Stan S. Robert Surinder P. Singh 《Journal of phycology》2010,46(5):917-925
The transgenic aerobic synthesis of long‐chain polyunsaturated fatty acids (LC‐PUFA) will in most land plants commence with either a Δ6‐desaturation or a Δ9‐elongation. Numerous Δ6‐desaturases have been characterized, but only one Δ9‐elongase has been reported in peer‐reviewed literature. In the present study, we describe the isolation of three additional Δ9‐elongases from the class Haptophyceae and demonstrate that the Δ9‐elongase group contains highly conserved regions, which differentiate them from other ELO‐type elongases. One such important difference is the presence of an LQxFHH motif instead of the usual LHxYHH motif, a feature that should simplify further gene discovery efforts in this group of enzymes. Moreover, the identification of the Pavlova salina (N. Carter) J. C. Green Δ9‐elongase completes the isolation of the entire P. salina docosahexaenoic acid (DHA) pathway, and we describe the assembly of this pathway in Nicotiana benthamiana. Finally, we comment on possible explanations for the widespread presence of the Δ6‐desaturated fatty acid stearidonic acid (SDA, 18:4Δ6,9,12,15) in the plastidial lipids of organisms using the Δ9‐elongase pathway. 相似文献