Structural insights into catalytic promiscuity of chalcone synthase from Glycine max (L.) Merr.: Coenzyme A-induced alteration of product specificity.

Catalytic promiscuity of enzymes plays a pivotal role in driving the evolution of plant specialized metabolism. Chalcone synthase (CHS) catalyzes the production of 2',4,4',6'-tetrahydroxychalcone (THC), a common precursor of plant flavonoids, from p-coumaroyl-coenzyme A (-CoA) and three malonyl-CoA molecules. CHS has promiscuous product specificity, producing a significant amount of p-coumaroyltriacetic lactone (CTAL) in vitro. However, mechanistic aspects of this CHS promiscuity remain to be clarified. Here, we show that the product specificity of soybean CHS (GmCHS1) is altered by CoA, a reaction product, which selectively inhibits THC production (IC50, 67 µM) and enhances CTAL production. We determined the structure of a ternary GmCHS1/CoA/naringenin complex, in which CoA is bound to the CoA-binding tunnel via interactions with Lys55, Arg58, and Lys268. Replacement of these residues by alanine resulted in an enhanced THC/CTAL production ratio, suggesting the role of these residues in the CoA-mediated alteration of product specificity. In the ternary complex, a mobile loop ("the K-loop"), which contains Lys268, was in a "closed conformation" placing over the CoA-binding tunnel, whereas in the apo and binary complex structures, the K-loop was in an "open conformation" and remote from the tunnel. We propose that the production of THC involves a transition of the K-loop conformation between the open and closed states, whereas synthesis of CTAL is independent of it. In the presence of CoA, an enzyme conformer with the closed K-loop conformation becomes increasingly dominant, hampering the transition of K-loop conformations to result in decreased THC production and increased CTAL production.

Varicella-zoster virus-associated meningitis, encephalitis, and myelitis with sporadic skin blisters: A case report.

BACKGROUND: Varicella-zoster virus (VZV) generally causes chickenpox at first infection in childhood and then establishes latent infection in the dorsal root ganglia of the spinal cord or other nerves. Virus reactivation owing to an impaired immune system causes inflammation along spinal nerves from the affected spinal segment, leading to skin manifestations (herpes zoster). Viremia and subsequent hematogenous transmission and nerve axonal transport of the virus may lead to meningitis, encephalitis, and myelitis. One such case is described in this study. CASE SUMMARY: A 64-year-old man presented with dysuria, pyrexia, and progressive disturbance in consciousness. He had signs of meningeal irritation, and cerebrospinal fluid (CSF) analysis revealed marked pleocytosis with mononuclear predominance and a CSF/serum glucose ratio of 0.64. Head magnetic resonance imaging revealed hyperintense areas in the frontal lobes. He had four isolated blisters with papules and halos on his right chest, right lumbar region, and left scapular region. Infected giant cells were detected using the Tzanck test. Degenerated epidermal cells with intranuclear inclusion bodies and ballooning degeneration were present on skin biopsy. Serum VZV antibody titers suggested previous infection, and the CSF tested positive for VZV-DNA. He developed paraplegia, decreased temperature perception in the legs, urinary retention, and fecal incontinence. The patient was diagnosed with meningitis, encephalitis, and myelitis and was treated with acyclovir for 23 days and prednisolone for 14 days. Despite gradual improvement, the urinary retention and gait disturbances persisted as sequelae. CONCLUSION: VZV reactivation should be considered in differential diagnoses of patients with sporadic blisters and unexplained central nervous system symptoms.

Crystal structure of chalcone synthase, a key enzyme for isoflavonoid biosynthesis in soybean.

Isoflavonoid is one of the groups of flavonoids that play pivotal roles in the survival of land plants. Chalcone synthase (CHS), the first enzyme of the isoflavonoid biosynthetic pathway, catalyzes the formation of a common isoflavonoid precursor. We have previously reported that an isozyme of soybean CHS (termed GmCHS1) is a key component of the isoflavonoid metabolon, a protein complex to enhance efficiency of isoflavonoid production. Here, we determined the crystal structure of GmCHS1 as a first step of understanding the metabolon structure, as well as to better understand the catalytic mechanism of GmCHS1.