Chemistry of α-mangostin. Studies on the semisynthesis of minor xanthones from <i>Garcinia mangostana</i>

<div><p>α-Mangostin is the major prenylated xanthone from <i>Garcinia mangostana</i> and it has been used also in recent times as starting material for the semisynthetic preparation of various biologically active derivatives. Its structure is characterised by the presence of few functional groups amenable to chemical manipulations, but present in the molecule in multiple instances (three phenolic hydroxyl groups, two prenyl chains and two unsubstituted aromatic carbons). This study represents a first approach to the systematic investigation of the reactivity of α-mangostin and describes the semisynthesis of some minor xanthones isolated from <i>G. mangostana</i>.</p></div

γ-PGA Hydrolases of Phage Origin in <i>Bacillus subtilis</i> and Other Microbial Genomes

<div><p>Poly-γ-glutamate (γ-PGA) is an industrially interesting polymer secreted mainly by members of the class <i>Bacilli</i> which forms a shield able to protect bacteria from phagocytosis and phages. Few enzymes are known to degrade γ-PGA; among them is a phage-encoded γ-PGA hydrolase, PghP. The supposed role of PghP in phages is to ensure access to the surface of bacterial cells by dismantling the γ-PGA barrier. We identified four unannotated <i>B</i>. <i>subtilis</i> genes through similarity of their encoded products to PghP; in fact these genes reside in prophage elements of <i>B</i>. <i>subtilis</i> genome. The recombinant products of two of them demonstrate efficient polymer degradation, confirming that sequence similarity reflects functional homology. Genes encoding similar γ-PGA hydrolases were identified in phages specific for the order Bacillales and in numerous microbial genomes, not only belonging to that order. The distribution of the γ-PGA biosynthesis operon was also investigated with a bioinformatics approach; it was found that the list of organisms endowed with γ-PGA biosynthetic functions is larger than expected and includes several pathogenic species. Moreover in non-Bacillales bacteria the predicted γ-PGA hydrolase genes are preferentially found in species that do not have the genetic asset for polymer production. Our findings suggest that γ-PGA hydrolase genes might have spread across microbial genomes via horizontal exchanges rather than via phage infection. We hypothesize that, in natural habitats rich in γ-PGA supplied by producer organisms, the availability of hydrolases that release glutamate oligomers from γ-PGA might be a beneficial trait under positive selection.</p></div

Relative distribution of <i>pghP</i> in bacteria and archaea genomes with respect to <i>pgsB</i>.

<p>In the Venn diagram green circles represent species that contain at least one <i>pghP</i>-like gene; violet circles represent species that contain <i>pgsB</i>. Numbers inside circles refer to the number of species containing either <i>pghP</i> or <i>pgsB</i>. Species that contain both genes are represented by the overlapping region in black (number inside). For each group (namely Archaea, total Bacteria, Bacillales, non-Bacillales) the size of circles and their overlapping region is drawn to scale. The raw data are available in the worksheet “Table of PghP and PgsB” contained in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130810#pone.0130810.s003" target="_blank">S1 Table</a>.</p

Degradation of <i>B</i>. <i>subtilis</i> γ-DL-PGA by YndL and YoqZ.

<p>A. <i>B</i>. <i>subtilis</i> γ-DL-PGA incubated with 0.045 μg YndL (lanes 2–5) or 0.009 μg YoqZ (lanes 7–10) at 37°C before separation on an agarose gel. Reactions were stopped after 1’ (lanes 2 and 7), 5’ (lanes 3 and 8), 10’ (lanes 4 and 9) and 20’ (lanes 5 and 10) by heating at 95°C for 3 min. Control reactions in lanes 1 and 6 were incubated for 20’ in the same conditions without enzyme. <b>B</b>. <i>B</i>. <i>subtilis</i> γ-DL-PGA was incubated at 37°C for 60’ with 0.5 μg YndL (lanes 2–5) or 0.5 μg YoqZ (lanes 6–9) with the addition of 10 mM (lanes 2 and 6), 50 mM (lanes 3 and 7), 100 mM (lanes 4 and 8) and 200 mM (lanes 5 and 9) EDTA. No enzyme was added in the control reaction in lane 1.</p

Purification of YndL and YoqZ.

<p>His-tagged YndL and YoqZ were purified from the insoluble <i>E</i>. <i>coli</i> lysate fraction using Ni-NTA agarose beads under denaturing conditions as described in Material and Methods. Lanes 1 and 6: 12 μL flow-through fractions; lanes 2 and 5: 1 μL beads; lanes 3 and 4: 6 μL eluted proteins. Lanes 1–3 refer to YndL purification; lanes 4–6 refer to YoqZ purification. Molecular weight markers are indicated on the left.</p

Clustal alignment of <i>B</i>. <i>subtilis</i> gene products showing similarity to <i>Bacillus</i> phage ΦNIT1 PghP.

<p>Black triangles below the sequences point to residues involved in Zn coordination according to the PghP structure [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130810#pone.0130810.ref031" target="_blank">31</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130810#pone.0130810.ref032" target="_blank">32</a>]. The valine residues enclosed in a rectangle in YoqZ and YndL sequences were transformed in the initial methionine in the recombinant proteins. An * (asterisk) in the clustal consensus line indicates positions which have a single, fully conserved residue. A: (colon) indicates conservation between groups of amino acids with strongly similar properties. A. (period) indicates conservation between groups of amino acids with weakly similar properties.</p

New ACE-Inhibitory Peptides from Hemp Seed (<i>Cannabis sativa</i> L.) Proteins

A hemp seed protein isolate, prepared from defatted hemp seed meals by alkaline solubilization/acid precipitation, was subjected to extensive chemical hydrolysis under acid conditions (6 M HCl). The resulting hydrolysate was fractionated by semipreparative RP-HPLC, and the purified fractions were tested as inhibitors of angiotensin converting enzyme (ACE). Mono- and bidimensional NMR experiments and LC-MS analyses led to the identification of four potentially bioactive peptides, i.e. GVLY, IEE, LGV, and RVR. They were prepared by solid-phase synthesis, and tested for ACE-inhibitory activity. The IC₅₀ values were GVLY 16 ± 1.5 μM, LGV 145 ± 13 μM, and RVR 526 ± 33 μM, confirming that hemp seed may be a valuable source of hypotensive peptides

<i>B. anthracis</i> γ-D-PGA is not a substrate for YndL and YoqZ.

<p><i>B</i>. <i>subtilis</i> γ-DL-PGA (2 μL in lanes 1–3), <i>B</i>. <i>anthracis</i> γ-D-PGA (2.5 μL lanes 4–6) or a mixture of both (2+2.5 μL in lanes 7–9) were incubated at 37°C for 60’ in the absence (lanes 1, 4, 7) or in the presence of 0.5 μg YndL (lanes 2, 5, 8) or 0.5 μg YoqZ (lanes 3, 6, 9). Enzymatic activity was stopped by heating at 95°C for 3 min before gel separation.</p