Evaluation and validation of an RT-PCR assay for specific detection of monkeypox virus (MPXV)

Monkeypox virus (MPXV) is a zoonotic orthopoxvirus within the Poxviridae family. MPXV is endemic to Central and West Africa. However, the world is currently witnessing an international outbreak with no clear epidemiological links to travel or animal exposure and with ever-increasing numbers of reported cases worldwide. Here, we evaluated and validated a new, sensitive, and specific real-time PCR-assay for MPXV diagnosis in humans and compare the performance of this novel assay against a Food & Drug Administration-cleared pan-Orthopox RT-PCR assay. We determined specificity, sensitivity, and analytic performance of the PKamp™ Monkeypox Virus RT-PCR assay targeting the viral F3L-gene. In addition, we further evaluated MPXV-PCR-positive specimens by viral culture, electron microscopy, and viral inactivation assays. The limit of detection was established at 7.2 genome copies/reaction, and MPXV was successfully identified in 20 clinical specimens with 100% correlation against the reference method with 100% sensitivity and specificity. Our results demonstrated the validity of this rapid, robust, and reliable RT-PCR assay for specific and accurate diagnosis of MPXV infection in human specimens collected both as dry swabs and in viral transport media. This assay has been approved by NYS Department of Health for clinical use.

Pre-steady-state study of recombinant sesquiterpene cyclases

An Escherichia coli expression system was used to generate hexahistidyl-tagged plant sesquiterpene cyclases, which were readily purified by a single affinity chromatographic step. Genes for Hyoscyamus muticus vetispiradiene synthase (HVS), a chimeric 5-epi-aristolochene synthase (CH3), and a chimeric sesquiterpene cyclase possessing multifunctional epi-aristolochene and vetispiradiene activity (CH4) were expressed in bacterial cells, which resulted in the sesquiterpene cyclases accumulating to 50% of the total protein and 35% of the soluble protein. From initial velocity experiments, the Michaelis constant for HVS was 3.5 microM, while CH3 and CH4 exhibited smaller values of 0.7 and 0.4 microM, respectively. Steady-state catalytic constants were from 0.02 to 0.04 s-1. A combination of pre-steady-state rapid quench experiments, isotope trapping experiments, and experiments to measure the burst rate constant as a function of substrate concentration revealed that turnover in all three cyclases is limited by a step after the initial chemical step involving rupture of the carbon-oxygen bond in farnesyl diphosphate (FPP). Rate constants for the limiting step were 10-70-fold smaller than for the initial chemical step. Dissociation constants for the enzyme-substrate complex (20-70 microM) were determined from the pre-steady-state experiments and were significantly larger than the observed Michaelis constants. A mechanism that involves an initial, rapid equilibration of enzyme with substrate to form an enzyme-substrate complex, followed by a slower conversion of FPP to an enzyme-bound hydrocarbon and a subsequent rate-limiting step, is proposed for the three enzymes. Interestingly, the multifunctional chimeric enzyme CH4 exhibited both a tighter binding of FPP and a faster conversion of FPP to products than either of its wild-type parents.