Semiempirical simulation of a theta‐class glutathione S‐transferase‐catalyzed glutathione attack to the allelochemical DIMBOA

Abstract

We evaluated by the semiempirical method PM3 possible mechanisms of a putative interaction between a cereal allelochemical, the cyclic hydroxamic acid 2,4dihydroxy-7-metoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA), and the tripeptide glutathione (GSH) inside the active site of a theta-class glutathione S-transferase. Based on a preliminary study of transition states from DIMBOA reactions with methanethiolate as a simple model of GSH, we investigated the roles of catalytic residues of the enzyme during nucleophilic additions of GSH to the carbonyl groups of DIMBOA and of its phenol/aldehyde isomer inside the active site model. Our results suggest that a tyrosine residue, Tyr113, makes the most important contributions for the catalytic mechanism. In the modeled reaction steps, Tyr113 behaves as a double hydrogen bond donor catalyst for nucleophilic additions of GSH to substrates: It initially helps stabilize the strongly nucleophilic reduced GSH with a hydrogen bond intermediated by a water molecule; during substrate approach, small conformational changes enable the residue to make a direct hydrogen bond to the substrate group that develop negative charge after addition of reduced GSH.

The Innate Immunity of Maize and the Dynamic Chemical Strategies Regulating Two-Component Signal Transduction in Agrobacterium tumefaciens

“…The decomposition of HDMBOA was followed from pH 3.5 to 13 in water and in methanol by 1 H NMR and UV spectroscopy. Under all conditions, the major decomposition product was MBOA , but the yield and the relative rate varied markedly (Figure . At pH 7.0, no HDMBOA was present by NMR after 15 min, being quantitatively converted to MBOA after 2.5 h (Figure ).…”

“…In a simple model for this mode of action, DIMBOA was shown to form imine adducts with the ɛ-NH 2 group of N-acetyllysine . DIMBOA was also shown to inhibit chymotrypsin activity by addition of the aldehyde to the active site serine , and a quantum mechanical model suggested that DIMBOA inhibits a glutathione S-transferase through reaction of the aldehyde with the thiol of reduced glutathione . Additionally, the cyclic hydroxamic acid of DIMBOA may also function as a thiol oxidant, generating a lactam (2-hydroxy-7-methoxy-benzoxazin-3-one, HMBOA, 3) as the reduction product .…”

“…These results suggest the rather intriguing possibility that the physical instability of the benzoxazinone antibiotics may not only create a steady-state local defense, but also enable a "pro-drug" strategy directed against bacterial environmental sensing. the active site serine (5 ), and a quantum mechanical model suggested that DIMBOA inhibits a glutathione Stransferase through reaction of the aldehyde with the thiol of reduced glutathione (6 ). Additionally, the cyclic hydroxamic acid of DIMBOA may also function as a thiol oxidant, generating a lactam (2hydroxy7 methoxybenzoxazin3one, HMBOA, 3) as the reduc tion product (7,8 ).…”

Secondary metabolites in plant innate immunity: conserved function of divergent chemicals

“…) can act as an electrophile in reactions with amino and thiol groups present in proteins and glutathione (Perez & Niemeyer, ; Dixon et al ., ). In line with this property, BX aglycones were shown to directly affect the activities of a wide range of enzymes, including papain (Perez & Niemeyer, ), α‐chymotrypsin (Cuevas et al ., ), glutathione S ‐transferase (Sant'anna et al ., ), and the plasma membrane‐resident H + ‐ATPase (Friebe et al ., ). For instance, in accordance with the proposed mechanism of action, the inhibition of α‐chymotrypsin results from the addition of aldehyde to catalytic serine (Cuevas et al ., ).…”