Enzymatic Synthesis of Aminoglycoside Antibiotics: Novel Adenosylmethionine:2-Deoxystreptamine N -Methyltransferase Activities in Hygromycin B- and Spectinomycin-Producing Streptomyces spp. and Uses of the Methylated Products

ABSTRACT Aminocyclitols structurally related to streptamine, a 1,3-diaminocyclitol, are common components of the RNA-binding aminoglycoside antibiotics. The respective aminocyclitol cores of hygromycin B and spectinomycin are N 3 -methyl-2-deoxy- d -streptamine and N 1 , N 3 -dimethyl-2- epi -streptamine. Adenosyl[ methyl - 14 C]methionine:2-deoxystreptamine N -methyltransferase activities were detected in extracts of early-stationary-phase mycelia of the hygromycin B producer Streptomyces hygroscopicus subsp. hygroscopicus ATCC 27438 and the spectinomycin producer Streptomyces flavopersicus ATCC 19756. Extracts of both strains methylated the N 1 - and N 3 -amino groups of 2-deoxystreptamine, streptamine, and 2- epi -streptamine; the N 1 -amino group of N 3 -methyl-2-deoxy- d -streptamine, and the N 3 -amino group of N 1 -ethyl-2-deoxy- d -streptamine, the semisynthetic aminocyclitol of netilmicin. The mono[ 14 C]methyl derivatives of 2-deoxystreptamine, streptamine, and 2- epi -streptamine were excellent substrates for l -glutamine:aminocyclitol aminotransferase and thereby provided a sensitive assay for derepression of this key enzyme, a generic biosynthetic marker that we have shown to be the only enzyme common to the biosyntheses of all major aminoglycoside antibiotics. Other prospective uses for these methyl-labeled 2-deoxystreptamine analogs are also described.