Biosynthesis of a 3,6-dideoxyhexose: crystallization and X-ray diffraction of CDP-6-deoxy-l- threo-d-­ glycero-4-hexulose-3-dehydrase (E1) for ascarylose biosynthesis.

CDP-6-deoxy-l- threo-d- glycero-4-hexulose-3-dehydrase (E1), along with its reductase (E3), catalyzes the unusual C-3 deoxygenation of CDP-6-deoxy-l-­ threo-d- glycero-4-hexulose to form CDP-3,6-dideoxy-l- threo-d- glycero-4-­hexulose in CDP-ascarylose biosynthesis [Chen et al. (1996), Biochemistry, 35, 16412–16420]. This dimeric [2Fe–2S] protein, cloned from the bacteria Yersinia pseudotuberculosis, is currently the only known example of an enzyme that uses a vitamin B6-derived pyridoxamine 5′-phosphate (PMP) cofactor to carry out one-electron chemistry [Agnihotri & Liu (2001), Bioorg. Chem. 29, 234–257]. It also exhibits a [2Fe–2S] cluster-binding motif (C- X57-C- X1-C- X7-C) which has not been observed previously [Agnihotri et al. (2004), Biochemistry, 43, 14265–14274] The recombinant 97.7 kDa dimer was crystallized in the trigonal space group P32, with unit-cell parameters a =  b = 97.37, c = 142.2 Å, α = β = 90, γ = 120°. A data set has been collected to 1.9 Å resolution. A full MAD data set was also collected at the iron absorption edge that diffracted to 2.0 Å. [ABSTRACT FROM AUTHOR]