Structural highlights
Publication Abstract from PubMedFor the field of virology, perhaps one of the most paradigm-shifting events so far in the 21(st) century was the identification of the giant double-stranded DNA virus that infects amoebae. Remarkably, this virus, known as Mimivirus, has a genome that encodes for nearly 1000 proteins, some of which are involved in the biosynthesis of unusual sugars. Indeed, the virus is coated by a layer of glycosylated fibers that contain d-glucose, N-acetyl-d-glucosamine, l-rhamnose, and 4-amino-4,6-dideoxy-d-glucose. Here we describe a combined structural and enzymological investigation of the protein encoded by the open-reading frame L780, which corresponds to an l-rhamnose synthase. The structure of the L780/NADP(+) /UDP-l-rhamnose ternary complex was determined to 1.45 A resolution and refined to an overall R-factor of 19.9 %. Each subunit of the dimeric protein adopts a bilobal-shaped appearance with the N-terminal domain harboring the dinucleotide binding site and the C-terminal domain positioning the UDP-sugar into the active site. The overall molecular architecture of L780 places it into the short chain dehydrogenase/reductase superfamily. Kinetic analyses indicate that the enzyme can function on either UDP- and dTDP-sugars but displays a higher catalytic efficiency with the UDP-linked substrate. Site-directed mutagenesis experiments suggest that both Cys 108 and Lys 175 play key roles in catalysis. This structure represents the first model of a viral UDP-l-rhamnose synthase and provides new details into these fascinating enzymes. This article is protected by copyright. All rights reserved. The High-Resolution Structure of a UDP-l-Rhamnose Synthase from Acanthamoeba polyphaga Mimivirus.,Bockhaus NJ, Ferek JD, Thoden JB, Holden HM Protein Sci. 2020 Aug 14. doi: 10.1002/pro.3928. PMID:32797646[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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