Expression, Purification, and Characterization of TylB, an Aminotransferase Involved in the Biosynthesis of Mycaminose

• Published in: Journal of the American Chemical Society Vol. 121; no. 30; pp. 7166 - 7167
• Main Authors: Chen, Huawei, Yeung, Siu-Man, Que, Nanette L. S, Müller, Thomas, Schmidt, Richard R, Liu, Hung-wen
• Format: Journal Article
• Language: English
• Published: American Chemical Society 04.08.1999
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja991213v

Amino sugars are ubiquitously found in nature as constituents of glycoproteins, glycolipids, and a great variety of secondary metabolites. They have been shown to contribute to the physiological functions of many glycoconjugates, and play pivotal roles in determining the efficacy and specificity of numerous clinically relevant natural products. For example, several of the lipopolysaccharide-based amino sugars are known to define the immunogenic characteristics of a specific bacterial strain. In addition, the common hydroxy/amino motif of the amino sugars in various aminoglycoside antibiotics has been demonstrated to be the key element responsible for the interaction between the antibiotics and their DNA/RNA targets. Biosynthetically, the amino sugars have been proposed to be derived from the corresponding keto sugars via a pyridoxal 5'-phosphate (PLP)-dependent transamination reaction. Recent genetic as well as phenotypic complementation studies of the biosynthesis of O-antigens and many sugar-containing secondary metabolites have accumulated a vast amount of information pertaining to unusual sugar formation. On the basis of the modest residue homology of the amino sugar biosynthetic genes to other available PLP-dependent enzymes, a number of these genes have been speculated to encode the aminotransferases for making amino sugars. In particular, studies of the biosynthesis of tylosin (1), a macrolide antibiotic that contains the 3,6-dideoxy-3-dimethyl-amino sugar mycaminose (2), has led to the assignment of tylB as the likely candidate encoding the requisite C-3 aminotransferase. The tentative assignment, of tylB along with other genes in the tylLM and tylIBA regions has allowed the postulation of a possible route for mycaminose biosynthesis as shown in Scheme 1. However, like most sugar biosynthetic genes, the corresponding gene products have never been isolated and characterized, and hence, the assignment of the actual catalytic role of tylB and other postulated aminotransferase genes awaits more concrete validation.