Engineering Bifunctional Enzymes Capable of Adenylating and Selectively Methylating the Side Chain or Core of Amino Acids

Nonribosomal peptides (NRPs) are known sources of therapeutics. Some nonribosomal peptide synthetase assembly lines contain unique functional interrupted adenylation (A) domains, where nature has combined two different functional domains into one bifunctional enzyme. Most often these interrupted A domains contain a part of a methylation (M) domain embedded in their sequence. Herein, we aimed to emulate nature and create fully functional interrupted A domains by inserting two different noncognate M domains, KtzH(M_H) and TioS(M_3S), into a naturally occurring uninterrupted A domain, Ecm6(A₁T₁). We evaluated the engineered enzymes, Ecm6(A_1aM_HA_1bT₁) and Ecm6(A_1aM_3SA_1bT₁), by a series of radiometric assays and found that not only do they maintain A domain activity, but also they gain the site-specific methylation patterns observed in the parent M domain donors. These findings provide an exciting proof-of-concept for generating interrupted A domains as future tools to modify NRPs and increase the diversity and activity of potential therapeutics.

Expanding Substrate Promiscuity by Engineering a Novel Adenylating-Methylating NRPS Bifunctional Enzyme

Nonribosomal peptides synthetases (NRPSs), which are multifunctional mega-enzymes producing many biologically active metabolites, are ideal targets for enzyme engineering. NRPS adenylation domains play a critical role in selecting/activating the amino acids to be transferred to downstream NRPS domains in the biosynthesis of natural products. Both monofunctional and bifunctional A domains interrupted with an auxiliary domain are found in nature. Here, we show that a bifunctional interrupted A domain can be uninterrupted by deleting its methyltransferase auxiliary domain portion to make an active monofunctional enzyme. We also demonstrate that a portion of an auxiliary domain with almost no sequence identity to the original auxiliary domain can be insert into naturally interrupted A domain to develop a new active bifunctional A domain with increased substrate profile. This work shows promise for the creation of new interrupted A domains in engineered NRPS enzymes.

Thiocoraline alters neuroendocrine phenotype and activates the Notch pathway in MTC-TT cell line

Medullary thyroid cancer (MTC) is an aggressive neuroendocrine tumor (NET). Previous research has shown that activation of Notch signaling has a tumor suppressor role in NETs. The potential therapeutic effect of thiocoraline on the activation of the Notch pathway in an MTC cell line (TT) was investigated. Thiocoraline was isolated from a marine bacterium Verrucosispora sp. MTT assay (3-[4, 5-dimethylthiazole-2-yl]-2, 5-diphenyltetrazolium bromide) was used to determine the IC₅₀ value and to measure cell proliferation. Western blot revealed the expression of Notch isoforms, NET, and cell cycle markers. Cell cycle progression was validated by flow cytometry. The mRNA expression of Notch isoforms and downstream targets were measured using real-time PCR. The IC₅₀ value for thiocoraline treatment in TT cells was determined to be 7.6 nmol/L. Thiocoraline treatment decreased cell proliferation in a dose- and time-dependent manner. The mechanism of growth inhibition was found to be cell cycle arrest in G1 phase. Thiocoraline activated the Notch pathway as demonstrated by the dose-dependent increase in mRNA and protein expression of Notch isoforms. Furthermore, treatment with thiocoraline resulted in changes in the expression of downstream targets of the Notch pathway (HES1, HES2, HES6, HEY1, and HEY2) and reduced expression of NET markers, CgA, and ASCL1. Thiocoraline is a potent Notch pathway activator and an inhibitor of MTC-TT cell proliferation at low nanomolar concentrations. These results provide exciting evidence for the use of thiocoraline as a potential treatment for intractable MTC.

Thiocoraline is a potent Notch pathway activator and an inhibitor of medullary thyroid cancer cell line (MTC-TT) cell proliferation at low nanomolar concentrations. These results provide evidence for the use of thiocoraline as a potential treatment for intractable MTC.

Mode of action of thiocoraline, a natural marine compound with anti-tumour activity

Thiocoraline, a new anticancer agent derived from the marine actinomycete Micromonospora marina, was found to induce profound perturbations of the cell cycle. On both LoVo and SW620 human colon cancer cell lines, thiocoraline caused an arrest in G1 phase of the cell cycle and a decrease in the rate of S phase progression towards G2/M phases, as assessed by using bromodeoxyuridine/DNA biparametric flow cytometric analysis. Thiocoraline does not inhibit DNA-topoisomerase II enzymes in vitro, nor does it induce DNA breakage in cells exposed to effective drug concentrations. The cell cycle effects observed after exposure to thiocoraline appear related to the inhibition of DNA replication. By using a primer extension assay it was found that thiocoraline inhibited DNA elongation by DNA polymerase alpha at concentrations that inhibited cell cycle progression and clonogenicity. These studies indicate that the new anticancer drug thiocoraline probably acts by inhibiting DNA polymerase alpha activity.