Calmodulin‐mediated suppression of 2‐ketoisovalerate reductase in Beauveria bassiana beauvericin biosynthetic pathway

Abstract

Ketoisovalerate reductase (KIVR, E.C. 1.2.7.7) mediates the specific reduction of 2-ketoisovalerate (2-Kiv) to d-hydroxyisovalerate (d-Hiv), a precursor for beauvericin biosynthesis. Beauvericin, a famous mycotoxin produced by many fungi, is a cyclooligomer depsipeptide, which has insecticidal, antimicrobial, antiviral, and cytotoxic activities. In this report, we demonstrated that Beauveria bassiana 2-ketoisovalerate reductase (BbKIVR) acts as a typical KIVR enzyme in the entomopathogenic fungus B. bassiana. In addition, we found that BbKIVR interacts with calmodulin (CaM) in vitro and in vivo. The functional role of CaM-binding to BbKIVR was to negatively regulate the BbKIVR activity in B. bassiana. Environmental stimuli such as light and salt stress suppressed BbKIVR activity in B. bassiana. Interestingly, this negative effect of BbKIVR activity by light and salt stress was recovered by CaM inhibitors, suggesting that the inhibitory mechanism is mediated through stimulation of CaM activity. Therefore, this work suggests that BbKIVR plays an important role in the beauvericin biosynthetic pathway mediated by environmental stimuli such as light and salt stress via the CaM signaling pathway.

Suppression of a methionine synthase by calmodulin under environmental stress in the entomopathogenic fungus Beauveria bassiana

“…2, His-BbMetE showed significant CaM-dependent inhibition on in vitro assay of MetE activity, indicating that CaM negatively regulates His-BbMetE activity. Many CaM-binding enzymes are negatively regulated by CaM in eukaryotes (Cyert, 2001;O'Day, 2003;Reddy et al, 2011) Recently, we reported two CaM-binding enzymes (BbPAL and BbKIVR) which are highly regulated by CaM in a negative manner (Kim et al, 2015;2016b). Basically, CaM can have the ability to induce a conformational change in BbMetE structure through direct interaction, and this alteration can directly affect the enzymatic activity of B. bassiana.…”

Integration of Untargeted Metabolomics with Transcriptomics Provides Insights into Beauvericin Biosynthesis in Cordyceps chanhua under H2O2-Induced Oxidative Stress

“…The result was consistent with the HPLC measurement of BEA. A previous report showed BbKIVR activity was suppressed under light and salt stress but not affected by oxidative stress in B. bassiana mycelia via the calmodulin (CaM) signaling pathway [ 62 ]. We found that oxidative stress promotes KIVR activity in C. chanhua mycelia.…”

Fusarium Cyclodepsipeptide Mycotoxins: Chemistry, Biosynthesis, and Occurrence

“…The depsipeptides, including BEAs, have a common 2-hydroxycarboxylic acid ingredient-D-2 -hydroxyisovalerate (D-Hiv) that is formed from 2-ketoisovalerate (2-Kiv) by a highly specific chiral reduction reaction catalyzed by 2-ketoisovalerate reductase (KIVR) enzyme [50,52,[67][68][69][70]. KIVR has a significant role in the biosynthesis of BEAs as was clearly understood when BEA production was inhibited in a KIVR knock-out B. bassiana mutant [67].…”

“…Kiv is formed from pyruvate during the biosynthesis of valine and it is the key intermediate in several metabolic pathways, including pantothenate biosynthesis in fungi, bacteria, and plants. It is also involved in producing phosphopantetheinyl prosthetic groups of acyl or peptidyl carrier proteins and co-enzyme A ( Figure 5) [50,52,67,69,70].…”