Category Archives: Emma Rackham

Diversity in natural product families is governed by more than enzyme promiscuity alone : establishing control of the pacidamycin portfolio

Sabine Grüschow ; Emma J. Rackham ; Rebecca J. M. Goss

Chem Sci 2011, 2 2182-2186

As with many other antibiotics, pacidamycins are produced as a suite of related compounds. Unlike most other secondary metabolites, however, this diversity is not solely the result of the substrate promiscuity of the biosynthetic enzymes but also arises from a gene duplication event (Pac21, Pac21h) and control of the precursor pool (PhhA). We are demonstrating the ability to harness these three levels of control in order to direct the selective production of specific members of this family of metabolites in a “dial-a-molecule” fashion. Furthermore, PhhA is shown to be a phenylalanine 3-hydroxylase, the first of the iron- and tetrahydropterin-dependentaromatic amino acid hydroxylases to be characterised with this regioselectivity.

Graphical abstract: Diversity in natural product families is governed by more than enzyme promiscuity alone: establishing control of the pacidamycin portfolio

Pacidamycin Biosynthesis : Identification and Heterologous Expression of the First Uridyl Peptide Antibiotic Gene Cluster

Emma J. Rackham ; Sabine Grüschow ; Amany E. Ragab ; Shilo Dickens ; Rebecca J. M. Goss

ChemBioChem 2010, 11 (12) 1700-1709

The pacidamycins are antimicrobial nucleoside antibiotics produced by Streptomyces coeruleorubidus that inhibit translocase I, an essential bacterial enzyme yet to be clinically targeted. The novel pacidamycin scaffold is composed of a pseudopeptide backbone linked by a unique exocyclic enamide to an atypical 3′-deoxyuridine nucleoside. In addition, the peptidyl chain undergoes a double inversion caused by the incorporation of a diamino acid residue and a rare internal ureido moiety. The pacidamycin gene cluster was identified and sequenced, thereby providing the first example of a biosynthetic cluster for a member of the uridyl peptide family of antibiotics. Analysis of the 22 ORFs provided an insight into the biosynthesis of the unique structural features of the pacidamycins. Heterologous expression in Streptomyces lividans resulted in the production of pacidamycin D and the newly identified pacidamycin S, thus confirming the identity of the pacidamycin biosynthetic gene cluster. Identification of this cluster will enable the generation of new uridyl peptide antibiotics through combinatorial biosynthesis. The concise cluster will provide a useful model system through which to gain a fundamental understanding of the way in which nonribosomal peptide synthetases interact.

New pacidamycins biosynthetically: probing N- and C-terminal substrate specificity

Amany E. Ragab ; Sabine Grüschow ; Emma J. Rackham ; Rebecca J. M. Goss

Org Biomol Chem 2010, 8 3128-3129

Feeding phenylalanine analogues to Streptomyces coeruleorubidus reveals the remarkable steric and electronic flexibility of this biosynthetic pathway and leads to the generation of a series of new halopacidamycins.

Graphical abstract: New pacidamycins biosynthetically: probing N- and C-terminal substrate specificity

New Pacidamycin Antibiotics Through Precursor-Directed Biosynthesis

Sabine Gruschow ; Emma J. Rackham ; Benjamin Elkins ; Philip L. A. Newilll ; Lionel M. Hill ; Rebecca J. M. Goss

ChemBioChem 2009, 10 (2) 355-360

Pacidamycins, mureidomycins and napsamycins are structurally related uridyl peptide antibiotics that inhibit translocase I, an as yet clinically unexploited target. This potentially important bioactivity coupled to the biosynthetically intriguing structure of pacidamycin make this natural product a fascinating subject for study. A precursor-directed biosynthesis approach was employed in order to access new pacidamycin derivatives. Strikingly, the biosynthetic machinery exhibited highly relaxed substrate specificity with the majority of the tryptophan analogues that were administered; this resulted in the production of new pacidamycin derivatives. Remarkably, 2-methyl-, 7-methyl-, 7-chloro- and 7-bromotryptophans produced their corresponding pacidamycin analogues in larger amounts than the natural pacidamycin. Low levels or no incorporation was observed for tryptophans substituted at positions 4, 5 and 6. The ability to generate bromo- and chloropacidamycins opens up the possibility of further functionalising these compounds through chemical cross-coupling in order to access a much larger family of derivatives.