The conversion of vitamin K epoxide to vitamin K quinone and vitamin K quinone to vitamin K hydroquinone uses the same active site cysteines

Vitamin K epoxide (or oxido) reductase (VKOR) is the target of warfarin and provides vitamin K hydroquinone for the carboxylation of select glutamic acid residues of the vitamin K-dependent proteins which are important for coagulation, signaling, and bone metabolism. It has been known for at least 20 years that cysteines are required for VKOR function. To investigate their importance, we mutated each of the seven cysteines in VKOR. In addition, we made VKOR with both C43 and C51 mutated to alanine (C43A/C51A), as well as a VKOR with residues C43-C51 deleted. Each mutated enzyme was purified and characterized. We report here that C132 and C135 of the CXXC motif are essential for both the conversion of vitamin K epoxide to vitamin K and the conversion of vitamin K to vitamin K hydroquinone. Surprisingly, conserved cysteines, 43 and 51, appear not to be important for either reaction. For the in vitro reaction driven by dithiothreitol, the 43-51 deletion mutation retained 85% and C43A/C51A 112% of the wild-type activity. The facile purification of the nine different mutations reported here illustrates the ease and reproducibility of VKOR purification by the method reported in our recent publication [Chu, P.-H., Huang, T.-Y., Williams, J., and Stafford, D. W. (2006) Proc. Natl. Acad. Sci. U S A. 103, 19308-19313].     

Brief communication: Extracellular enzymatic activities of dermatophytes

Eighty dermatophyte strains belonging to the genera Trichophyton, Microsporum, Epidermophyton and Chrysosporium were screened for their ability to produce extracellular enzymes using a semiquantitative method. The results obtained vary significantly when the studied genera are observed separately, though the enzyme -galactosidase was detected in none of the four studied genera.     

The effect of corticosteroids on serum fungistatic activity

The direct impairment of a serum fungistatic factor has been postulated as a mechanism to account for the greater severity of cutaneous fungal disease in patients treated with corticosteroids.Trichophyton mentagrophytes andTrichophyton rubrum were grown on Mycosel® agar containing increasing concentrations of normal human sera and sera from patients with Cushing's syndrome and from those receiving high doses of prednisone. Fungistatic activity, observed as a retardation of the normal growth pattern, was not significantly different in any of the sera tested.     

A hetero-dimer model for concerted action of vitamin K carboxylase and vitamin K reductase in vitamin K cycle

Vitamin K carboxylase (VKC) is believed to convert vitamin K, in the vitamin K cycle, to an alkoxide-epoxide form which then reacts with CO₂ and glutamate to generate γ-carboxyglutamic acid (Gla). Subsequently, vitamin K epoxide reductase (VKOR) is thought to convert the alkoxide-epoxide to a hydroquinone form. By recycling vitamin K, the two integral-membrane proteins, VKC and VKOR, maintain vitamin K levels and sustain the blood coagulation cascade. Unfortunately, NMR or X-ray crystal structures of the two proteins have not been characterized. Thus, our understanding of the vitamin K cycle is only partial at the molecular level. In this study, based on prior biochemical experiments on VKC and VKOR, we propose a hetero-dimeric form of VKC and VKOR that may explain the efficient oxidation and reduction of vitamin K during the vitamin K cycle.     

Biological activities of two fungistatic antibiotics produced by Bacillus cereus UW85.

Cultures and culture filtrates of Bacillus cereus UW85 suppress damping-off of alfalfa caused by Phytophthora medicaginis. We studied the role in disease suppression of two antibiotics from culture filtrates of UW85 that reversibly inhibited growth of P. medicaginis. We purified the two antibiotics by cation-exchange chromatography and high-voltage paper electrophoresis and showed that one of them, designated zwittermicin A, was an aminopolyol of 396 Da that was cationic at pH 7.0; the second, designated antibiotic B, appeared to be an aminoglycoside containing a disaccharide. Both antibiotics prevented disease of alfalfa seedlings caused by P. medicaginis. Purified zwittermicin A reversibly reduced elongation of germ tubes derived from cysts of P. medicaginis, and antibiotic B caused swelling of the germ tubes. Mutants generated with Tn917 or mitomycin C treatment were screened either for antibiotic accumulation in an agar plate diffusion assay or for the ability to suppress damping-off disease of alfalfa. Of 2,682 mutants screened for antibiotic accumulation, 5 mutants were substantially reduced in antibiotic accumulation and disease-suppressive activity. Of the 1,700 mutants screened for disease-suppressive activity, 3 mutants had reduced activity and they accumulated less of both antibiotics than did the parent strain. The amount of antibiotic accumulated by the mutants was significantly correlated with the level of disease suppression. Addition of either zwittermicin A or antibiotic B to alfalfa plants inoculated with a culture of a nonsuppressive mutant resulted in disease suppression. These results demonstrate that B. cereus UW85 produces two fungistatic antibiotics that contribute to suppression of damping-off disease of alfalfa.     

Microcolony imaging of Aspergillus fumigatus treated with echinocandins reveals both fungistatic and fungicidal activities

Background

The echinocandins are lipopeptides that can be employed as antifungal drugs that inhibit the synthesis of 1,3-β-glucans within the fungal cell wall. Anidulafungin and caspofungin are echinocandins used in the treatment of Candida infections and have activity against other fungi including Aspergillus fumigatus. The echinocandins are generally considered fungistatic against Aspergillus species.

Methods

Culture of A. fumigatus from conidia to microcolonies on a support of porous aluminium oxide (PAO), combined with fluorescence microscopy and scanning electron microscopy, was used to investigate the effects of anidulafungin and caspofungin. The PAO was an effective matrix for conidial germination and microcolony growth. Additionally, PAO supports could be moved between agar plates containing different concentrations of echinocandins to change dosage and to investigate the recovery of fungal microcolonies from these drugs. Culture on PAO combined with microscopy and image analysis permits quantitative studies on microcolony growth with the flexibility of adding or removing antifungal agents, dyes, fixatives or osmotic stresses during growth with minimal disturbance of fungal microcolonies.

Significance

Anidulafungin and caspofungin reduced but did not halt growth at the microcony level; additionally both drugs killed individual cells, particularly at concentrations around the MIC. Intact but not lysed cells showed rapid recovery when the drugs were removed. The classification of these drugs as either fungistatic or fungicidal is simplistic. Microcolony analysis on PAO appears to be a valuable tool to investigate the action of antifungal agents.     

Relationship of dithiothreitol-dependent microsomal vitamin K quinone and vitamin K epoxide reductases inhibition of epoxide reduction by vitamin K quinone

Vitamin K quinone was shown to be an effective inhibitor of vitamin K epoxide reduction by whole rat liver microsomes. Observation of inhibition was dependent upon the mode of addition of the substrate and inhibitor suggesting segregation of the compounds into different microsomal vesicles under certain conditions. The result is consistent with reduction of both vitamin K quinone and vitamin K epoxide by a single enzyme or a multisite enzyme complex.     

Lapachol inhibition of vitamin K epoxide reductase and vitamin K quinone reductase

Lapachol [2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphthoquinone] has been shown to be a potent inhibitor of both vitamin K epoxide reductase and the dithiothreitol-dependent vitamin K quinone reductase of rat liver microsomes in vitro. These observations explain the anticoagulant activity of lapachol previously observed in both rats and humans. Lapachol inhibition of the vitamin K epoxide and quinone reductases resembled coumarin anticoagulant inhibition, and was observed in normal strain but not in warfarin-resistant strain rat liver microsomes. This similarity of action suggests that the lactone functionality of the coumarins is not critical for their activity. The initial-velocity steady-state inhibition patterns for lapachol inhibition of the solubilized vitamin K epoxide reductase were consistent with tight binding of lapachol to the oxidized form of the enzyme, and somewhat lower affinity for the reduced form. It is proposed that lapachol assumes a 4-enol tautomeric structure similar to that of the 4-hydroxy coumarins. These structures are analogs of the postulated hydroxyvitamin K enolate intermediate bound to the oxidized form of the enzyme in the chemical reaction mechanism of vitamin K epoxide reductase, thus explaining their high affinity.     

6种抗真菌药物对皮肤癣菌体外抗真菌活性评价

目的评价6种抗真菌药物对皮肤癣菌体外抗真菌活性。方法采用CLSI推荐的M-38P方案对分离自足癣和体、股癣的皮肤癣菌进行联苯苄唑、硝酸舍他康唑、硝酸异康唑、盐酸布替萘芬、阿莫洛芬、利拉萘酯6种抗真菌药物敏感性测定。结果联苯苄唑MIC范围为0．03—4mg／L,MIC50为1mg／L,MIC90为2mg／L。硝酸舍他康唑分别为0．06—16mg／L、0．5mg／L和2mg／L。硝酸异康唑分别为0．03～2mg／L、0．25mg／L和0．5mg／L。盐酸布替萘芬分别为0．0025～0．04mg／L、0．01mg／L和0．02mg／L。阿莫罗芬分别为0．01～〉0．08mg／L、0．02mg／L和0．04mg／L。利拉萘酯分别为0．004—0．625mg／L、0．039mg／L和0．312mg／L。结论6种抗真菌药物对皮肤癣菌均有强的抗菌活性,由强到弱依次为布替萘芬、阿莫罗芬、利拉萘酯和咪唑类药物。     

The fungistatic activity of ethylenic and acetylenic compounds; the fungistatic activity of tetraiodoethylene and related compounds

The high fungistatic activity of tetraiodoethylene has been investigated. Diiodo-acetylene, which like tetraiodoethylene is an unsaturated substance containing only carbon and iodine, has also been found to have a high antifungal action. The effect of replacing the iodine atoms in these compounds by hydrogen, bromine, and carboxyl and nitro groups has been studied. The high fungistatic activity of some iodoethylenic and iodoacetylenic compounds appears to be associated with the presence in the molecule of positive iodine.