View source for 4pgg


==Caffeic acid O-methyltransferase from Sorghum bicolor==
<StructureSection load='4pgg' size='340' side='right'caption='[[4pgg]], [[Resolution|resolution]] 2.02&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[4pgg]] is a 2 chain structure with sequence from [https://en.wikipedia.org/wiki/Sorghum_bicolor Sorghum bicolor]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=4PGG OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=4PGG FirstGlance]. <br>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">X-ray diffraction, [[Resolution|Resolution]] 2.015&#8491;</td></tr>
<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=4pgg FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=4pgg OCA], [https://pdbe.org/4pgg PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=4pgg RCSB], [https://www.ebi.ac.uk/pdbsum/4pgg PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=4pgg ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/C5YH12_SORBI C5YH12_SORBI] 
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
Using S-adenosylmethionine as the methyl donor, caffeic acid O-methyltransferase from Sorghum bicolor (SbCOMT) methylates the 5-hydroxyl group of its preferred substrate, 5-hydroxyconiferaldehyde. In order to determine the mechanism of SbCOMT and understand the observed reduction in the lignin syringyl-to-guaiacyl ratio of three brown midrib12 (bmr12) mutants that carry COMT gene missense mutations, we determined the apo-form and S-adenosylmethionine-binary complex SbCOMT crystal structures, and established the ternary complex structure with 5-hydroxyconiferaldehyde by molecular modeling. These structures revealed many features shared with monocot ryegrass (Lolium perenne) and dicot alfalfa (Medicago sativa) COMTs. SbCOMT steady-state kinetic and calorimetric data suggest a random bi-bi mechanism. Based on our structural, kinetic and thermodynamic results, we propose that the observed reactivity hierarchy among 4,5-dihydroxy-3-methoxycinnamyl (and 3,4-dihydroxycinnamyl) aldehyde, alcohol and acid substrates arises from the ability of the aldehyde to stabilize the anionic intermediate that results from deprotonation of the 5-hydroxyl group by His267. Additionally, despite the presence of other phenylpropanoid substrates in vivo, sinapaldehyde is the preferential product, as demonstrated by its low Km for 5-hydroxyconiferaldehyde. Unlike its acid and alcohol substrates, the aldehydes exhibit product inhibition and we propose this is due to non-productive binding of the s-cis-form of the aldehydes inhibiting productive binding of the s-trans-form. The s-cis-aldehydes most likely act only as inhibitors because the high rotational energy barrier around the 2-propenyl bond prevents s-trans conversion, unlike alcohol substrates whose low 2-propenyl bond rotational energy barrier enables rapid s-cis/s-trans interconversion.

Determination of the structure and catalytic mechanism of Sorghum bicolor caffeic acid O-methyltransferase and the structural impact of three brown midrib12 mutations.,Green AR, Lewis KM, Barr JT, Jones JP, Lu F, Ralph J, Vermerris W, Sattler SE, Kang C Plant Physiol. 2014 Jun 19. pii: pp.114.241729. PMID:24948836<ref>PMID:24948836</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
</div>
<div class="pdbe-citations 4pgg" style="background-color:#fffaf0;"></div>
== References ==
<references/>
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</StructureSection>
[[Category: Large Structures]]
[[Category: Sorghum bicolor]]
[[Category: Green AR]]
[[Category: Kang C]]
[[Category: Lewis KM]]