Insights into Methyltransferase Specificity and Bioactivity of Derivatives of the Antibiotic Plantazolicin

Abstract

Peptide antibiotics represent a class of conformationally-constrained natural products of growing pharmaceutical interest. Plantazolicin (PZN) is a linear, polyheterocyclic natural product with highly selective and potent activity against the anthrax-causing bacterium, Bacillus anthracis. The bioactivity of PZN is contingent on dimethylation of its N-terminal Arg residue by an S-adenosylmethionine-dependent methyltransferase. Here, we explore the substrate tolerances of two homologous PZN methyltransferases by carrying out kinetic analyses of the enzymes against a synthetic panel of truncated PZN analogs containing the N-terminal Arg residue. X-ray cocrystal structures of the PZN methyltransferases with each of these heterocycle-containing substrates provide a rationale for understanding the strict substrate specificity of these enzymes. Kinetic studies of structure-guided, site-specific variants allowed for the assignment of residues governing catalysis and substrate scope. Microbiological testing further revealed that upon dimethylation of the N-terminal Arg, a pentaheterocyclized PZN analog retained potent anti-B. anthracis activity, nearly equal to that of full-length PZN. These studies may be useful in the biosynthetic engineering of natural product analogs with different bioactivity profiles, as demonstrated by our identification of a truncated plantazolicin derivative that is active against methicillin-resistant Staphylococcus aureus (MRSA).

Recent advances in methyltransferase biocatalysis

“…[ 31,32] The crystal structures of two MTase enzymes involved in benzylisoquinoline alkaloid biosynthesis have also recently been elucidated, the pavine-N-methyltransferase (PNMT) and norcoclaurine-6-O-methyltransferase (6OMT) ( Figure 2B). [33,34] The characterization of MTases from these pathways could be useful in developing biocatalytic approaches for production of alkaloid derivatives, which have been widely used as pharmaceuticals.…”

“…[38] The improved structural understanding of both O-MTase and N-MTase active sites can now be used to expand the substrate range of these enzymes, increasing their value as biocatalysts with non-native substrates ( Figure 2B). [1,12,16,32,34,36] The mammalian catechol O-methyltransferase (COMT) is involved in catabolism of catecholamines such as dopamine. The active site of COMT is close to the enzyme surface, enabling a variety of non-native catechol substrates to be methylated (16).…”

Complete genome of mangrove-derived anti-MRSA streptomycete, Streptomyces pluripotens MUSC 135T

“…Among these gene clusters, one of them was found to be responsible for production of linear azol(in)e-containing peptides (LAPs). The members of LAPs family, such as goadsporin and plantazolicin have previously been detected from microbes have shown potent antibacterial activities against pathogens including Bacillus anthracis and MRSA [26][27][28] . In conclusion, we report the complete A sequence of S. pluripotens MUSC 135 T .…”

Targeted treatment for bacterial infections: prospects for pathogen-specific antibiotics coupled with rapid diagnostics

“…129,130 Plantazolicin has selective activity against Bacillus anthracis but the biological target has not yet been reported. 131,132 The semisynthetic lanthipeptide NVB302 (from the natural product deoxyactagardine B) is another example of a ribosomal peptide-derived, pathogen-specific antibiotic (Fig. 4); 133 it has recently completed a phase I clinical trial for the selective treatment of C. difficile .…”