Identification and characterization of the point mutation which affects the transcription level of the chromosomal 3-N-acetyltransferase gene of Streptomyces griseus SS-1198

Basic and applied research on multiple aminoglycoside antibiotic resistance of actinomycetes: an old-timer's recollection

A list of our research achievements on multiple aminoglycoside antibiotic (AG) resistance in AG-producing actinomycetes is outlined. In 1979, the author discovered a novel AG (istamycin)-producing Streptomyces tenjimariensis SS-939 by screening actinomycetes with kanamycin (KM)-resistance and plasmid profiles. This discovery directed our biochemical and genetic approaches to multiple AG resistance (AGR) of AG producers. In this article, the following discoveries will be outlined: (1) AGR profiles correlating with the productivity of AGs in AG-producers, (2) Wide distribution of multiple AG resistance in AG-nonproducing actinomycetes, (3) Involvement of ribosomal resistance and AG-acetylating enzymes as underlying AGR factors, (4) Activation by single nucleotide substitution of a silent gene coding for aminoglycoside 3-N-acetyltransferase, AAC(3), in S. griseus, (5) Discovery of a novel antibiotic indolizomycin through protoplast fusion treatment between S. tenjimariensis and S. griseus strains with different AGR phenotypes, and (6) Double stage-acting activity of arbekacin (ABK; an anti-MRSA semisynthetic AG) discovered by acetylation of ABK with cloned AACs; that is both ABK and its acetylated derivatives showed remarkable antibiotic activities.

Small-Molecule Acetylation by GCN5-Related N-Acetyltransferases in Bacteria

Acetylation is a conserved modification used to regulate a variety of cellular pathways, such as gene expression, protein synthesis, detoxification, and virulence. Acetyltransferase enzymes transfer an acetyl moiety, usually from acetyl coenzyme A (AcCoA), onto a target substrate, thereby modulating activity or stability. Members of the GCN5- N -acetyltransferase (GNAT) protein superfamily are found in all domains of life and are characterized by a core structural domain architecture. These enzymes can modify primary amines of small molecules or of lysyl residues of proteins. From the initial discovery of antibiotic acetylation, GNATs have been shown to modify a myriad of small-molecule substrates, including tRNAs, polyamines, cell wall components, and other toxins. This review focuses on the literature on small-molecule substrates of GNATs in bacteria, including structural examples, to understand ligand binding and catalysis. Understanding the plethora and versatility of substrates helps frame the role of acetylation within the larger context of bacterial cellular physiology.

Aminoglycoside modifying enzymes

Aminoglycosides have been an essential component of the armamentarium in the treatment of life-threatening infections. Unfortunately, their efficacy has been reduced by the surge and dissemination of resistance. In some cases the levels of resistance reached the point that rendered them virtually useless. Among many known mechanisms of resistance to aminoglycosides, enzymatic modification is the most prevalent in the clinical setting. Aminoglycoside modifying enzymes catalyze the modification at different -OH or -NH₂ groups of the 2-deoxystreptamine nucleus or the sugar moieties and can be nucleotidyltransferases, phosphotransferases, or acetyltransferases. The number of aminoglycoside modifying enzymes identified to date as well as the genetic environments where the coding genes are located is impressive and there is virtually no bacteria that is unable to support enzymatic resistance to aminoglycosides. Aside from the development of new aminoglycosides refractory to as many as possible modifying enzymes there are currently two main strategies being pursued to overcome the action of aminoglycoside modifying enzymes. Their successful development would extend the useful life of existing antibiotics that have proven effective in the treatment of infections. These strategies consist of the development of inhibitors of the enzymatic action or of the expression of the modifying enzymes.