5KVA

Crystal Structure of sorghum caffeoyl-CoA O-methyltransferase (CCoAOMT)

Summary for 5KVA

• Entry DOI: 10.2210/pdb5kva/pdb
• Descriptor: caffeoyl-CoA O-methyltransferase, S-ADENOSYLMETHIONINE, CALCIUM ION, ... (4 entities in total)
• Functional Keywords: caffeoyl-coa o-methyltransferase, sbccoaomt, ccoaomt, ccomt omt, sam o-methyltransferase, methyltransferase, coenzyme a, transferase
• Biological source: Sorghum bicolor (Sorghum)
• Total number of polymer chains: 2
• Total formula weight: 62979.41

Authors

Walker, A.M.,Sattler, S.A.,Regner, M.,Jones, J.P.,Ralph, J.,Vermerris, W.,Sattler, S.E.,Kang, C. (deposition date: 2016-07-14, release date: 2016-08-10, Last modification date: 2024-03-06)

Primary citation

Walker, A.M.,Sattler, S.A.,Regner, M.,Jones, J.P.,Ralph, J.,Vermerris, W.,Sattler, S.E.,Kang, C.
The Structure and Catalytic Mechanism of Sorghum bicolor Caffeoyl-CoA O-Methyltransferase.
Plant Physiol., 172:78-92, 2016

PubMed Abstract: 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 Ca(2+) in the active site, lowering the pKa 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.

PubMed: 27457122
DOI: 10.1104/pp.16.00845

Experimental method

X-RAY DIFFRACTION (1.827 Å)