Purification and Characterization of 2-Deoxy-scyllo-inosose Synthase Derived from Bacillus circulans. A Crucial Carbocyclization Enzyme in the Biosynthesis of 2-Deoxystreptamine-containing Aminoglycoside Antibiotics.

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Abstract
The biosynthesis of 2-deoxystreptamine, the central aglycon of a major group of clinically important aminoglycoside antibiotics, commences with the initial carbocycle formation step from D-glucose-6-phosphate to 2-deoxy-15-cyllo-inosose. This crucial step is known to be catalyzed by 2-deoxy-scyllo-inosose synthase, which has not yet been characterized so far. Reported in this paper is the first purification of 2-deoxy-scyllo-inosose synthase from butirosin-producing. Bacillus circulans SANK 72073 to electrophoretic homogeneity. The enzyme was isolated as a heterodimeric protein comprising from a 23 kDa- and a 42 kDa polypeptide chains. The Km of the enzyme for D-glucose-6-phosphate was estimated to be 9.O × 10-4M and that for NAD+ 1.7 × 10-4M, kcat for D-glucose-6-phosphate being 7.3 × 10-2s-1. The presence of Co2+ was essential for the enzyme activity, but Zn2+ was totally inhibitory. While the reaction mechanisms are quite similar, 2-deoxy-scyllo-inosose synthase appears to be distinct from dehydroquinate synthase in the shikimate pathway, with respect to the quaternary structure, metal ion requirement, and the kinetic parameters.

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