Acyl Donor Stringency and Dehydroaminoacyl Intermediates in β-Lactam Formation by a Non-ribosomal Peptide Synthetase

High-throughput reprogramming of an NRPS condensation domain

Engineered biosynthetic assembly lines could revolutionize the sustainable production of bioactive natural product analogs. Although yeast display is a proven, powerful tool for altering the substrate specificity of gatekeeper adenylation domains in nonribosomal peptide synthetases (NRPSs), comparable strategies for other components of these megaenzymes have not been described. Here we report a high-throughput approach for engineering condensation (C) domains responsible for peptide elongation. We show that a 120-kDa NRPS module, displayed in functional form on yeast, can productively interact with an upstream module, provided in solution, to produce amide products tethered to the yeast surface. Using this system to screen a large C-domain library, we reprogrammed a surfactin synthetase module to accept a fatty acid donor, increasing catalytic efficiency for this noncanonical substrate >40-fold. Because C domains can function as selectivity filters in NRPSs, this methodology should facilitate the precision engineering of these molecular assembly lines.

The dabABC operon is a marker of C4-alkylated monobactam biosynthesis and responsible for (2S,3R)-diaminobutyrate production

Non-ribosomal peptide synthetases (NRPSs) assemble metabolites of medicinal and commercial value. Both serine and threonine figure prominently in these processes and separately can be converted to the additional NRPS building blocks 2,3-diaminopropionate (Dap) and 2,3-diaminobutyrate (Dab). Here we bring extensive bioinformatics, in vivo and in vitro experimentation to compose a unified view of the biosynthesis of these widely distributed non-canonical amino acids that both derive by pyridoxal-mediated β-elimination of the activated O-phosphorylated substrates followed by β-addition of an amine donor. By examining monobactam biosynthesis in Pseudomonas and in Burkholderia species where it is silent, we show that (2S,3R)-Dab synthesis depends on an l-threonine kinase (DabA), a β-replacement reaction with l-aspartate (DabB) and an argininosuccinate lyase-like protein (DabC). The growing clinical importance of monobactams to both withstand Ambler Class B metallo-β-lactamases and retain their antibiotic activity make reprogrammed precursor and NRPS synthesis of modified monobactams a feasible and attractive goal.

Labelling studies in the biosynthesis of polyketides and non-ribosomal peptides

Covering: 2015 to 2022In this review, we discuss the recent advances in the use of isotopically labelled compounds to investigate the biosynthesis of polyketides, non-ribosomally synthesised peptides, and their hybrids. Also, we highlight the use of isotopes in the elucidation of their structures and investigation of enzyme mechanisms. The biosynthetic pathways of selected examples are presented in detail to reveal the principles of the discussed labelling experiments. The presented examples demonstrate that the application of isotopically labelled compounds is still the state of the art and can provide valuable information for the biosynthesis of natural products.

Structural Studies of Modular Nonribosomal Peptide Synthetases

The non-ribosomal peptide synthetases (NRPSs) are a family of modular enzymes involved in the production of peptide natural products. Not restricted by the constraints of ribosomal peptide and protein production, the NRPSs are able to incorporate unusual amino acids and other suitable building blocks into the final product. The NRPSs operate with an assembly line strategy in which peptide intermediates are covalently tethered to a peptidyl carrier protein and transported to different catalytic domains for the multiple steps in the biosynthesis. Often the carrier and catalytic domains are joined into a single large multidomain protein. This chapter serves to introduce the NRPS enzymes, using the nocardicin NRPS system as an example that highlights many common features to NRPS biochemistry. We then describe recent advances in the structural biology of NRPSs focusing on large multidomain structures that have been determined.

Structure and Function of a Dehydrating Condensation Domain in Nonribosomal Peptide Biosynthesis

Dehydroamino acids are important structural motifs and biosynthetic intermediates for natural products. Many bioactive natural products of nonribosomal origin contain dehydroamino acids; however, the biosynthesis of dehydroamino acids in most nonribosomal peptides is not well understood. Here, we provide biochemical and bioinformatic evidence in support of the role of a unique class of condensation domains in dehydration (C_modAA). We also obtain the crystal structure of a C_modAA domain, which is part of the nonribosomal peptide synthetase AmbE in the biosynthesis of the antibiotic methoxyvinylglycine. Biochemical analysis reveals that AmbE-C_modAA modifies a peptide substrate that is attached to the donor carrier protein. Mutational studies of AmbE-C_modAA identify several key residues for activity, including four residues that are mostly conserved in the C_modAA subfamily. Alanine mutation of these conserved residues either significantly increases or decreases AmbE activity. AmbE exhibits a dimeric conformation, which is uncommon and could enable transfer of an intermediate between different protomers. Our discovery highlights a central dehydrating function for C_modAA domains that unifies dehydroamino acid biosynthesis in diverse nonribosomal peptide pathways. Our work also begins to shed light on the mechanism of C_modAA domains. Understanding C_modAA domain function may facilitate identification of new natural products that contain dehydroamino acids and enable engineering of dehydroamino acids into nonribosomal peptides.

CAN: A new program to streamline preparation of molecular coordinate files for molecular dynamics simulations

Preparing molecular coordinate files for molecular dynamics (MD) simulations can be a very time-consuming process. Herein we present the development of a user-friendly program that drastically reduces the time required to prepare these molecular coordinate files for MD software packages such as AmberTools. Our program, known as charge atomtype naming (CAN), creates and uses a library of structures such as amino acid monomers to update the charge, atom type, and name of atoms in any molecular structure (mol2) file. We demonstrate the utility of this new program by rapidly preparing structural files for MD simulations for polypeptides ranging from small molecules to large protein structures. Both native and non-native amino acid residues are easily handled by this new program.