Catechol-O-methyltransferase (COMT, EC 2.1.1.6) catalyzes the O-methylation of a wide array of catechol-containing substrates using s-adenosyl-L-methionine as the methyl donor. In the present study, we have cloned and expressed the human soluble and membrane-bound COMTs (S-COMT and MB-COMT, respectively) in Escherichia coli and have studied their biochemical characteristics for the O-methylation of representative classes of endogenous catechol substrates (catecholamines and catechol estrogens) as well as exogenous catechol substrates (bioflavonoids and tea catechins). Enzyme kinetic analyses showed that these two recombinant human COMTs are functionally active, with catalytic and kinetic properties nearly identical to those of crude or purified enzymes prepared from human tissues or cells. Kinetic parameters for the O-methylation of various substrates were characterized. In addition, computational modeling studies were conducted to better understand the molecular mechanisms for the different catalytic behaviors of human S- and MB-COMTs with respect to s-adenosyl-L-methionine, various substrates, and also the regioselectivity for the formation of mono-methyl ether products. Our modeling data showed that the binding energy values (Delta G) calculated for most substrates agreed well with the measured kinetic parameters. Also, our modeling data precisely predicted the regioselectivity for the O-methylation of these substrates at different hydroxyl groups, the predicted values matched nearly perfectly with the experimental data.

The impacts of climate change on agricultural production are a global concern and have already begun to occur (1, 2), with major drivers including warmer temperatures and the occurrence of extreme weather events (3-8). An important dimension of the climate change-crop yield relationship that has often been overlooked in the empirical literature is the influence that warming temperatures can have on plant damage arriving through biotic channels, such as pest infestation or fungal infection (5). Aflatoxins are carcinogenic chemicals produced by the fungi Aspergillus flavus and A. parasiticus, which commonly infect food crops. Currently, in the United States, aflatoxin is a perennial contaminant in corn grown in the South, but rare in the Corn Belt and northern states. Climate change may expand aflatoxin’s geographical prevalence, however; because hot, dry summers promote aflatoxin accumulation. Here we model aflatoxin risk as a function of corn plant growth stages and weather to predict US regions with high aflatoxin risk in 2031-2040, based on sixteen climate change models. Our results suggest that over 89.5% of corn-growing counties in fifteen states, including the Corn Belt, will experience increased aflatoxin contamination in 2031-2040 compared to 2011-2020. Interestingly, the results are spatially heterogeneous and include several Southern counties expected to have lower aflatoxin risk, because the causative fungi become inactivated at very high temperatures.