Substrate recognition and modification by the nosiheptide resistance methyltransferase

Thiopeptides: antibiotics with unique chemical structures and diverse biological activities

Thiopeptides are a class of natural product antibiotics with diverse structures and functions. Their complex structures and biosynthesis have intrigued researchers since their discovery in 1948, but not a single thiopeptide has been approved for human use. This is mainly due to their poor solubility, challenging synthesis, and low bioavailability. This review summarizes the current research on the biosynthesis and biological activity of thiopeptide antibiotics since 2015. The focus of research since 2015 has been on uncovering biosynthetic routes, developing methods for total synthesis, and understanding the biological activity of thiopeptides. Overall, there is still much to learn about this family of molecules.

YcaO-Dependent Posttranslational Amide Activation: Biosynthesis, Structure, and Function

With advances in sequencing technology, uncharacterized proteins and domains of unknown function (DUFs) are rapidly accumulating in sequence databases and offer an opportunity to discover new protein chemistry and reaction mechanisms. The focus of this review, the formerly enigmatic YcaO superfamily (DUF181), has been found to catalyze a unique phosphorylation of a ribosomal peptide backbone amide upon attack by different nucleophiles. Established nucleophiles are the side chains of Cys, Ser, and Thr which gives rise to azoline/azole biosynthesis in ribosomally synthesized and posttranslationally modified peptide (RiPP) natural products. However, much remains unknown about the potential for YcaO proteins to collaborate with other nucleophiles. Recent work suggests potential in forming thioamides, macroamidines, and possibly additional post-translational modifications. This review covers all knowledge through mid-2016 regarding the biosynthetic gene clusters (BGCs), natural products, functions, mechanisms, and applications of YcaO proteins and outlines likely future research directions for this protein superfamily.

Functional roles in S-adenosyl-L-methionine binding and catalysis for active site residues of the thiostrepton resistance methyltransferase

Resistance to the antibiotic thiostrepton, in producing Streptomycetes, is conferred by the S-adenosyl-L-methionine (SAM)-dependent SPOUT methyltransferase Tsr. For this and related enzymes, the roles of active site amino acids have been inadequately described. Herein, we have probed SAM interactions in the Tsr active site by investigating the catalytic activity and the thermodynamics of SAM binding by site-directed Tsr mutants. Two arginine residues were demonstrated to be critical for binding, one of which appears to participate in the catalytic reaction. Additionally, evidence consistent with the involvement of an asparagine in the structural organization of the SAM binding site is presented.