Biosynthesis Pathways for Deoxysugars in Antibiotic-Producing Actinomycetes: Isolation, Characterization and Generation of Novel Glycosylated Derivatives

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Abstract
Many bioactive natural products synthesized by actinomycetes are glycosylated compounds in which the appended sugars contribute to specific interactions with their biological target. Most of these sugars are 6-deoxyhexoses, of which more than 70 different forms have been identified, and an increasing number of gene clusters involved in 6-deoxyhexoses biosynthesis are being characterized from antibiotic-producing actinomycetes. Novel glycosylated compounds have been generated by modifying natural deoxysugar biosynthesis pathways in the producer organisms, and/or the simultaneous expression in these strains of selected deoxysugar biosynthesis genes from other strains. Non-producing strains endowed with the capacity to synthesize novel deoxysugars through the expression of engineered deoxysugar biosynthesis clusters can also be used as alternative hosts. Transfer of these deoxysugars to a multiplicity of aglycones relies upon the existence of glycosyltransferases with an inherent degree of 'relaxed substrate specificity'. In this review, we analyze how the knowledge coming out from isolation and characterization of deoxysugar biosynthesis pathways from actinomycetes is being used to produce novel glycosylated derivatives of natural products.