Structural and functional characterization of the glutathione peroxidase-like thioredoxin peroxidase from the fungus Trichoderma reesei.

Glutathione peroxidases (GPx) are a family of enzymes with the ability to reduce organic and inorganic hydroperoxides to the corresponding alcohols using glutathione or thioredoxin as an electron donor. Here, we report the functional and structural characterization of a GPx identified in Trichoderma reesei (TrGPx). TrGPx was recombinantly expressed in a bacterial host and purified using affinity. Using a thioredoxin coupled assay, TrGPx exhibited activity of 28 U and 12.5 U in the presence of the substrates H2O2 and t-BOOH, respectively, and no activity was observed when glutathione was used. These results indicated that TrGPx is a thioredoxin peroxidase and hydrolyses H2O2 better than t-BOOH. TrGPx kinetic parameters using a pyrogallol assay resulted at Kmapp = 11.7 mM, Vmaxapp = 10.9 IU/µg TrGPx, kcat = 19 s-1 and a catalytic efficiency of 1.6 mM-1 s-1 to H2O2 as substrate. Besides that, TrGPx demonstrated an optimum pH ranging from 9.0-12.0 and a half-life of 36 min at 80 °C. TrGPx 3D-structure was obtained in a reduced state and non-catalytic conformation. The overall fold is similar to the other phospholipid-hydroperoxide glutathione peroxidases. These data contribute to understand the antioxidant mechanism in fungi and provide information for using antioxidant enzymes in biotechnological applications.

Structural and functional characterization of the glutathione peroxidase-like thioredoxin peroxidase from the fungus Trichoderma reesei

Glutathione peroxidases (GPx) are a family of enzymes with the ability to reduce organic and inorganic hydroperoxides to the corresponding alcohols using glutathione or thioredoxin as an electron donor. Here, we report the functional and structural characterization of a GPx identified in Trichoderma reesei (TrGPx). TrGPx was recombinantly expressed in a bacterial host and purified using affinity. Using a thioredoxin coupled assay, TrGPx exhibited activity of 28 U and 12.5 U in the presence of the substrates H2O2 and t-BOOH, respectively, and no activity was observed when glutathione was used. These results indicated that TrGPx is a thioredoxin peroxidase and hydrolyses H2O2 better than t-BOOH. TrGPx kinetic parameters using a pyrogallol assay resulted at Kmapp = 11.7 mM, Vmaxapp = 10.9 IU/μg TrGPx, kcat = 19 s−1 and a catalytic efficiency of 1.6 mM−1 s−1 to H2O2 as substrate. Besides that, TrGPx demonstrated an optimum pH ranging from 9.0–12.0 and a half-life of 36 min at 80 °C. TrGPx 3D-structure was obtained in a reduced state and non-catalytic conformation. The overall fold is similar to the other phospholipid-hydroperoxide glutathione peroxidases. These data contribute to understand the antioxidant mechanism in fungi and provide information for using antioxidant enzymes in biotechnological applications.

The crystal structure of AjiA1 reveals a novel structural motion mechanism in the adenylate-forming enzyme family.

Adenylate-forming enzymes (AFEs) are a mechanistic superfamily of proteins that are involved in many cellular roles. In the biosynthesis of benzoxazole antibiotics, an AFE has been reported to play a key role in the condensation of cyclic molecules. In the biosynthetic gene cluster for the benzoxazole AJI9561, AjiA1 catalyzes the condensation of two 3-hydroxyanthranilic acid (3-HAA) molecules using ATP as a co-substrate. Here, the enzymatic activity of AjiA1 is reported together with a structural analysis of its apo form. The structure of AjiA1 was solved at 2.0 Šresolution and shows a conserved fold with other AFE family members. AjiA1 exhibits activity in the presence of 3-HAA (Km = 77.86 ± 28.36, kcat = 0.04 ± 0.004) and also with the alternative substrate 3-hydroxybenzoic acid (3-HBA; Km = 22.12 ± 31.35, kcat = 0.08 ± 0.005). The structure of AjiA1 in the apo form also reveals crucial conformational changes that occur during the catalytic cycle of this enzyme which have not been described for any other AFE member. Consequently, the results shown here provide insights into this protein family and a new subgroup is proposed for enzymes that are involved in benzoxazole-ring formation.

Identification, In Vitro Testing and Molecular Docking Studies of Microginins' Mechanism of Angiotensin-Converting Enzyme Inhibition.

Cyanobacteria are able to produce a wide range of secondary metabolites, including toxins and protease inhibitors, with diverse biological activities. Microginins are small linear peptides biosynthesized by cyanobacteria species that act against proteases. The aim of this study was to isolate and identify microginins produced by the LTPNA08 strain of Microcystis aeruginosa, as well as to verify their potential to inhibit angiotensin-converting enzyme (ACE; EC. 3.4.15.1) using in vitro and in silico methods. The fractionation of cyanobacterial extracts was performed by liquid chromatography and the presence of microginins was monitored by both LC-MS and an ACE inhibition assay. Enzyme inhibition was assayed by ACE with hippuryl-histidyl-leucine as the substrate; monitoring of hippuric acid was performed by HPLC-DAD. Isolated microginins were confirmed by mass spectrometry and were used to carry out the enzymatic assay. Molecular docking was used to evaluate microginin 770 (MG 770) and captopril (positive control), in order to predict similar binding interactions and determine the inhibitory action of ACE. The enzyme assay confirmed that MG 770 can efficiently inhibit ACE, with an IC50 equivalent to other microginins. MG 770 presented with comparable interactions with ACE, having features in common with commercial inhibitors such as captopril and enalaprilate, which are frequently used in the treatment of hypertension in humans.