Christopher A. Kauffman

The genetic architecture of atrial fibrillation (AF) encompasses low impact, common genetic variants and high impact, rare variants. Here, we characterize a high impact AF-susceptibility allele, KCNQ1 R231H, and describe its transcontinental geographic distribution and history. Induced pluripotent stem cell-derived cardiomyocytes procured from risk allele carriers exhibit abbreviated action potential duration, consistent with a gain-of-function effect. Using identity-by-descent (IBD) networks, we estimate the broad- and fine-scale population ancestry of risk allele carriers and their relatives. Analysis of ancestral migration routes reveals ancestors who inhabited Denmark in the 1700s, migrated to the Northeastern United States in the early 1800s, and traveled across the Midwest to arrive in Utah in the late 1800s. IBD/coalescent-based allele dating analysis reveals a relatively recent origin of the AF risk allele (~5000 years). Thus, our approach broadens the scope of study for disease susceptibility alleles to the context of human migration and ancestral origins.

Analysis of the full genome of an environmentally-unique, halotolerant Streptomyces sp. strain GSL-6C, isolated from the Great Salt Lake, revealed a gene cluster encoding the biosynthesis of the salinipeptins, D-amino acid containing members of the rare linaridin subfamily of ribosomally synthesized and post-translationally modified peptides (RiPPs). The sequence organization of the unmodified amino acid residues in salinipeptins A–D (1–4) were suggested by genome annotation, and subsequently their sequence and post-translational modifications were defined using a range of spectroscopic techniques and chemical derivatization approaches. The salinipeptins are unprecedented linaridins bearing nine D-amino acids, which are uncommon in RiPP natural products and are the first reported in the linaridin subfamily. Whole genome mining of GSL-6C did not reveal any homologs of the reported genes responsible for amino acid epimerization in RiPPs, inferring new epimerases may be involved in the conversion of L- to D-amino acids. In addition, the N-oxide and dimethylimidazolidin-4-one moieties in salinipeptins B and C, which are modified from N,N-dimethylalanine, are unknown in bacterial peptides. The three-dimensional structure of salinipeptin A, possessing four loops generated by significant hydrogen bonding, was established based on observed nuclear Overhauser effect (NOE) correlations. This study demonstrates that integration of genomic information early in chemical analysis significantly facilitates the discovery and structure characterization of novel microbial secondary metabolites.

Chemical investigation of a marine actinomycete within the family Streptomycetaceae (our strain CNQ-149) has led to the isolation of the unprecedented alkaloids, actinobenzoquinoline (1) and actinophenanthrolines A–C (2–4). The chemical structures of 1–4 were assigned by interpretation of NMR spectroscopic data, and their absolute configurations were assigned by X-ray analysis. Actinobenzoquinoline possesses a 5-methyloxazolidin-4-one moiety and a dihydrobenzo[h]quinoline core structure, while actinophenanthrolines A–C are composed of hydroxypropanamide-substituted 1,7-phenanthroline core skeletons.

The microbial production, isolation, and structure elucidation of four new napyradiomycin congeners (1–4) is reported. The structures of these compounds, which are new additions to the marine-derived meroterpenoids, were defined by comprehensive spectroscopic analysis and by X-ray crystallography. Using fluorescence-activated cell sorting (FACS) analysis, napyradiomycins 1–4 were observed to induce apoptosis in the colon adenocarcinoma cell line HCT-116, indicating the possibility of a specific biochemical target for this class of cytotoxins.

The isolation and structure elucidation of a new meroterpenoid, actinoranone (1), produced by a marine bacterium closely related to the genus Streptomyces is reported. Actinoranone is composed of an unprecedented dihydronaphthalenone polyketide linked to a bicyclic diterpenoid. The stereochemistry of 1 was defined by application of the advanced Mosher’s method and by interpretation of spectroscopic data. Actinoranone (1) is significantly cytotoxic to HCT-116 human colon cancer cells with an LD₅₀ = 2.0 μg/mL.

Licensed to kill: A new antibiotic, anthracimycin (see scheme), produced by a marine‐derived actinomycete in saline culture, shows significant activity toward Bacillus anthracis, the bacterial pathogen responsible for anthrax infections. Chlorination of anthracimycin gives a dichloro derivative that retains activity against Gram‐positive bacteria, such as anthrax, but also shows activity against selected Gram‐negative bacteria.

Cyanosporasides are marine bacterial natural products containing a chlorinated cyclopenta[a]indene core of suspected enediyne polyketide biosynthetic origin. Herein, we report the isolation and characterization of novel cyanosporasides C–F (3–6) from the marine actinomycetes Salinispora pacifica CNS-143 and Streptomyces sp. CNT-179, highlighted by the unprecedented C-2′ N-acetylcysteamine functionalized hexose group of 6. Cloning, sequencing, and mutagenesis of homologous ∼50 kb cyanosporaside biosynthetic gene clusters from both bacteria afforded the first genetic evidence supporting cyanosporaside’s enediyne, and thereby p-benzyne biradical, biosynthetic origin and revealed the molecular basis for nitrile and glycosyl functionalization. This study provides new opportunities for bioengineering of enediyne derivatives and expands the structural diversity afforded by enediyne gene clusters.