Isolation of -L-glutaminyl 4-hydroxybenzene and -L-glutaminyl 3,4-benzoquinone: a natural sulfhydryl reagent, from sporulating gill tissue of the mushroom Agaricus bisporus

Chemical Structures, Biological Activities, and Biosynthetic Analysis of Secondary Metabolites from Agaricus Mushrooms: A Review

Agaricus mushrooms are an important genus in the Agaricaceae family, belonging to the order Agaricales of the class Basidiomycota. Among them, Agaricus bisporus is a common mushroom for mass consumption, which is not only nutritious but also possesses significant medicinal properties such as anticancer, antibacterial, antioxidant, and immunomodulatory properties. The rare edible mushroom, Agaricus blazei, contains unique agaricol compounds with significant anticancer activity against liver cancer. Agaricus blazei is believed to expel wind and cold, i.e., the pathogenic factors of wind and cold from the body, and is an important formula in traditional Chinese medicine. Despite its nutritional richness and outstanding medicinal value, Agaricus mushrooms have not been systematically compiled and summarized. Therefore, the present review compiles and classifies 70 natural products extracted from Agaricus mushrooms over the past six decades. These compounds exhibit diverse biological and pharmacological activities, with particular emphasis on antitumor and antioxidant properties. While A. blazei and A. bisporus are the primary producers of these compounds, studies on secondary metabolites from other Agaricus species remain limited. Further research is needed to explore and understand the anticancer and nutritional properties of Agaricus mushrooms. This review contributes to the understanding of the structure, bioactivity, and biosynthetic pathways of Agaricus compounds and provides insights for the development of functional foods using these mushrooms.

Mushroom Tyrosinase: Six Isoenzymes Catalyzing Distinct Reactions

"Mushroom tyrosinase" from the common button mushroom is the most frequently used source of tyrosinase activity, both for basic and applied research. Here, the complete tyrosinase family from Agaricus bisporus var. bisporus (abPPO1-6) was cloned from mRNA and expressed heterologously using a single protocol. All six isoenzymes accept a wide range of phenolic and catecholic substrates, but display pronounced differences in their specificity and enzymatic reaction rate. AbPPO3 ignores γ-l-glutaminyl-4-hydroxybenzene (GHB), a natural phenol present in mM concentrations in A. bisporus, while AbPPO4 processes 100 μM GHB at 4-times the rate of the catechol l-DOPA. All six AbPPOs are biochemically distinct enzymes fit for different roles in the fungal life cycle, which challenges the traditional concept of isoenzymes as catalyzing the same physiological reaction and varying only in secondary properties. Transferring this approach to other enzymes and organisms will greatly stimulate both the study of the in vivo function(s) of enzymes and the application of these highly efficient catalysts.

The pro-enzyme C-terminal processing domain of Pholiota nameko tyrosinase is responsible for folding of the N-terminal catalytic domain

Pholiota nameko (Pholiota microspore) tyrosinase is expressed as a latent 67-kDa pro-tyrosinase, comprising a 42-kDa N-terminal catalytic domain with a binuclear copper centre and a 25-kDa C-terminal domain and is activated by proteolytic digestion of the C-terminal domain. To investigate the role of the C-terminal processing domain of pro-tyrosinase, we constructed a recombinant tyrosinase lacking the C-terminal domain and four recombinant pro-tyrosinase mutants (F515G, H539N, L540G and Y543G) carrying substituted amino acid residues on the C-terminal domain. The recombinant tyrosinase lacking the C-terminal domain had no catalytic activity; whereas the mutant L540G was copper depleted, the other mutants had copper contents similar to that of the wild-type pro-tyrosinase. Proteolytic digestion activated the mutants H539N and Y543G following release of the C-terminal domain, and the resulting tyrosinases had higher K m values for t-butyl catechol than the wild-type pro-tyrosinase. The mutants F515G and L540G were degraded by proteolytic digestion and yielded smaller proteins with no activity. These data suggest that the C-terminal processing domain of P. nameko pro-tyrosinase is essential for correct folding of the N-terminal catalytic domain and acts as an intramolecular chaperone during assembly of the active-site conformation.

Uridine-based inhibitors as new leads for antibiotics targeting Escherichia coli LpxC

The UDP-3-O-(R-3-hydroxyacyl)-N-acetylglucosamine deacetylase LpxC catalyzes the committed reaction of lipid A (endotoxin) biosynthesis in Gram-negative bacteria and is a validated antibiotic target. Although several previously described compounds bind to the unique acyl chain binding passage of LpxC with high affinity, strategies to target the enzyme's UDP-binding site have not been reported. Here the identification of a series of uridine-based LpxC inhibitors is presented. The most potent examined, 1-68A, is a pH-dependent, two-step, covalent inhibitor of Escherichia coli LpxC that competes with UDP to bind the enzyme in the first step of inhibition. Compound 1-68A exhibits a K(I) of 54 muM and a maximal rate of inactivation (k(inact)) of 1.7 min(-1) at pH 7.4. Dithiothreitol, glutathione and the C207A mutant of E. coli LpxC prevent the formation of a covalent complex by 1-68A, suggesting a role for Cys-207 in inhibition. The inhibitory activity of 1-68A and a panel of synthetic analogues identified moieties necessary for inhibition. 1-68A and a 2-dehydroxy analogue, 1-68Aa, inhibit several purified LpxC orthologues. These compounds may provide new scaffolds for extension of existing LpxC-inhibiting antibiotics to target the UDP binding pocket.

The laccase gene family in Coprinopsis cinerea (Coprinus cinereus)

In this study, we isolated and sequenced eight non-allelic laccase genes from Coprinopsis cinerea ( Coprinus cinereus) homokaryon AmutBmut. These eight genes represent the largest laccase gene family identified so far in a single haploid fungal genome. We analyzed the phylogenetic relationships between these genes by intron positions, amino acid sequence conservation and similarities in promoter sequences. All deduced protein products have the laccase signature sequences L1-L4, the typical conserved cysteine and the ten histidine residues which are ligands in the two laccase copper-binding centers, T1 and T2/T3. Proteins Lcc2 and Lcc3 of Coprinopsis cinerea are most similar to the acidic, membrane-associated laccase CLAC2 from Coprinellus congregatus implicated in neutralization of acidic medium. All other laccases from the saprophyte Coprinopsis cinerea, including the well described enzyme Lcc1, form a cluster separate from these three enzymes and from various laccases of wood-rotting and plant-pathogenic basidiomycetes.

Inhibition of enzymatic browning and protection of sulfhydryl enzymes by thiol compounds

In a reaction between (-)-epicatechin (EC) and 2-mercaptoethanol (2ME), catalyzed by partially purified polyphenol oxidase (PPO) extracted from the style of Rhododendron mucronatum, 2'-(2-hydroxyethylthio)-(-)-epicatechin (2'-HETEC), 5'-(2-hydroxyethylthio)-(-)-epicatechin (5'-HETEC), and 2',5'-bis(2-hydroxyethylthio)-(-)-epicatechin (2',5'-HETEC) were formed. The rate of formation of 2',5'-HETEC from 5'-HETEC was faster than that from 2'-HETEC. In the absence of 2ME, the concentration of EC decreased rapidly and the reaction mixture turned brown; 2'-, 5'-, and 2',5'-HETEC, especially 2'-substituted HETECs. reacted more slowly. These data indicate that 2ME acts both as an inhibitor of the polymerization of O-quinone, presumably by binding to it and as a reductant involved in the conversion of O-quinone to O-dihydroxyphenol, Inhibition of enzymatic browning by other thiol compounds such as cysteine and dithiothreitol was also investigated.

Concerning the role of mitochondria in cryptobiosis

The metabolic characteristics of the mitochondria of Agaricus bisporus are altered in the zygote by specific inhibitors that permit them to retain structural integrity in the dormant spore and enable them to initiate energy production, with apparent protein synthesis and replication during the initial phase of germination. The insensitivity of the earliest events of germination to selective cytoplasmic and nuclear inhibitors characterizes this as a transient period of unusual mitochondrial autonomy. To define the intrinsic metabolic potentials of the organelle and its role in cryptobiosis, mitochondria were fractionated aseptically from presporulating zygotes and were placed in dialysis chambers surrounded by nutrient media at 15 C. For periods through 48 hours, the isolated mitochondria manifested the capacity to incorporate labeled amino acids linearly into proteins and retained stable electrophoretic protein profiles for more than 5 days. They maintained fine structural integrity for at least 10 days, some developed septational membranes, and they increased numerically. These metabolic activities were dependent upon a nutrient substrate.

Cytostatic, cytocidal and potential antitumor properties of a class of quinoid compounds, initiators of the dormant state in the spores of Agaricus bisporus

Evidence indicates that dormancy is initiated in the spores of Agaricus bisporus by two quinoid compounds that appear in the zygote during the prodromal period of sporulation. Both are derivatives of a phenol, gamma-L-glutaminyl-4-hydroxybenzene. When purified, these quinoids specifically inhibit mitochondrial respiratory enzymes and protein synthesis in the mushroom and have comparable effects with rat liver mitochondria and ribosomes, with intact bacteria, and with bacterial ribosomes and RNA polymerase in vitro. Five species of mouse ascites tumor cells showed prompt and marked inhibitions of nucleic acid and protein synthesis when millimolar concentrations of these quinoids were added to the tissue culture medium of the tumor cells. Only a small percentage of the cells was killed immediately, as judged by trypan blue uptake. When large numbers of exposed BP8 sarcoma and EL4 leukemic cells were reinjected intraperitoneally into histocompatible mice, the survival times of these animals were notably prolonged beyond those of animals injected with tumor cells that had not been exposed to these inhibitors. In a dose-dependent manner, increasing concentrations of inhibitors produced proportionate increments in survival time, while higher concentrations totally abolished tumor cell growth. The findings indicate that these simple quinoid compounds, which initiate the dormant state in spores, produce a cytostatic state in mammalian tumor cells and thus potentially have strong antitumor properties (Am J Pathol 78:33-48, 1975).

Study of phenoloxidase activity during the reproductive cycle in Schizophyllum commune

A study of the temporal relationship between the appearance of phenoloxidase activity and the formation of fruiting bodies in Schizophyllum commune was undertaken. The results indicate that phenoloxidase activity increases in colonies subsequent to the formation of aggregate masses of hyphae, continues to increase until mature, sporulating fruiting structures are produced, and then declines significantly.