Journal
PLANT PHYSIOLOGY
Volume 172, Issue 1, Pages 78-92Publisher
AMER SOC PLANT BIOLOGISTS
DOI: 10.1104/pp.16.00845
Keywords
-
Categories
Funding
- National Science Foundation [MCB 102114, CHE 118359]
- National Institutes of Health [1R01GM11125401]
- M.J. Murdock Charitable Trust
- Biomass Research and Development Initiative [2011-1006-30358]
- U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies Office [DE-PI0000031]
- Department of Energy Great Lakes Bioenergy Research Center [DE-FC02-07ER64494]
- U.S. Department of Agriculture (National Institute of Food and Agriculture AFRI grant) [2011-67009-30026]
- U.S. Department of Agriculture (CRIS project) [3042-21220-032-00D]
- ARS [ARS-0424223, 813387] Funding Source: Federal RePORTER
Ask authors/readers for more resources
Caffeoyl-coenzyme A 3-O-methyltransferase (CCoAOMT) is an S-adenosyl methionine (SAM)-dependent O-methyltransferase responsible for methylation of the meta-hydroxyl group of caffeoyl-coenzyme A (CoA) on the pathway to monolignols, with their ring methoxylation status characteristic of guaiacyl or syringyl units in lignin. In order to better understand the unique class of type 2 O-methyltransferases from monocots, we have characterized CCoAOMT from sorghum(Sorghum bicolor; SbCCoAOMT), including the SAM binary complex crystal structure and steady-state enzyme kinetics. Key amino acid residues were validated with site-directed mutagenesis. Isothermal titration calorimetry data indicated a sequential binding mechanism for SbCCoAOMT, wherein SAM binds prior to caffeoyl-CoA, and the enzyme showed allosteric behavior with respect to it. 5-Hydroxyferuloyl-CoA was not a substrate for SbCCoAOMT. We propose a catalytic mechanism in which lysine-180 acts as a catalytic base and deprotonates the reactive hydroxyl group of caffeoyl-CoA. This deprotonation is facilitated by the coordination of the reactive hydroxyl group by Ca2+ in the active site, lowering the pK(a) of the 3'-OH group. Collectively, these data give a new perspective on the catalytic mechanism of CCoAOMTs and provide a basis for the functional diversity exhibited by type 2 plant OMTs that contain a unique insertion loop (residues 208-231) conferring affinity for phenylpropanoid-CoA thioesters. The structural model of SbCCoAOMT can serve as the basis for protein engineering approaches to enhance the nutritional, agronomic, and industrially relevant properties of sorghum.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available