Carrier Protein Interaction with Competing Adenylation and Epimerization Domains in a Nonribosomal Peptide Synthetase Analyzed by FRET

In multi-domain nonribosomal peptide synthetases (NRPSs) the order of domains and their catalytic specificities dictate the structure of the peptide product. Peptidyl-carrier proteins (PCPs) bind activated amino acids and channel elongating peptidyl intermediates along the protein template. To this end, fine-tuned interactions with the catalytic domains and large-scale PCP translocations are necessary. Despite crystal structure snapshots of several PCP-domain interactions, the conformational dynamics under catalytic conditions in solution remain poorly understood. We report a FRET reporter of gramicidin S synthetase 1 (GrsA; with A-PCP-E domains) to study for the first time the interaction between PCP and adenylation (A) domain in the presence of an epimerization (E) domain, a competing downstream partner for the PCP. Bulk FRET measurements showed that upon PCP aminoacylation a conformational shift towards PCP binding to the A domain occurs, indicating the E domain acts on its PCP substrate out of a disfavored conformational equilibrium. Furthermore, the A domain was found to preferably bind the D-Phe-S-Ppant-PCP stereoisomer, suggesting it helps in establishing the stereoisomeric mixture in favor of the D-aminoacyl moiety. These observations surprisingly show that the conformational logic can deviate from the order of domains and thus reveal new principles in the multi-domain interplay of NRPSs.

A dissected non-ribosomal peptide synthetase maintains activity

Non-ribosomal peptide synthetases (NRPSs) generate chemically complex compounds and their modular architecture suggests that changing their domain organization can predictably alter their products. Ebony, a small three-domain NRPS, catalyzes the formation of β-alanine containing amides from biogenic amines. To examine the necessity of interdomain interactions, we modeled and docked domains of Ebony to reveal potential interfaces between them. Testing the same domain combinations in vitro showed that 8 % of activity was preserved after Ebony was dissected into a di-domain and a detached C-terminal domain, suggesting that sufficient interaction was maintained after dissection. Our work creates a model to identify domain interfaces necessary for catalysis, an important step toward utilizing Ebony as a combinatorial engineering platform for novel amides.

Molecular diversity and function of jasmintides from Jasminum sambac

BACKGROUND

Jasmintides jS1 and jS2 from Jasminum sambac were previously identified as a novel family of cysteine-rich peptides (CRPs) with an unusual disulfide connectivity. However, very little else is known about jasmintides, particularly their molecular diversity and functions. Here, we report the discovery and characterization of a novel suite of jasmintides from J. sambac using transcriptomic, peptidomic, structural and functional tools.

RESULTS

Transcriptomic analysis of leaves, flowers and roots revealed 14 unique jasmintide precursors, all of which possess a three-domain architecture comprising a signal peptide, a pro-domain and a mature jasmintide domain. Peptidomic analysis, using fractionated mixtures of jasmintides and chemical derivatization of cysteine to pseudolysine, trypsin digestion and MS/MS sequencing, revealed an additional 86 jasmintides, some of which were post-translationally modified. NMR analysis showed that jasmintide jS3 has three anti-parallel β-strands with a three-disulfide connectivity of CysI-CysV, CysII-CysIV and CysIII-CysVI, which is similar to jasmintide jS1. Jasmintide jS3 was able to withstand thermal, acidic and enzymatic degradation and, importantly, exhibited antifeedant activity against mealworm Tenebrio molitor.

CONCLUSION

Together, this study expands the existing library of jasmintides and furthers our understanding of the molecular diversity and cystine framework of CRPs as scaffolds and tools for engineering peptides targeting pests.