Unique Aggregation of Sterigmatocystin in Water Yields Strong and Specific Circular Dichroism Response Allowing Highly Sensitive and Selective Monitoring of Bio-Relevant Interactions.

Daniela Jakšić,Ivo Piantanida,Gennaro Pescitelli,Vilko Smrečki,Maja Šegvić Klarić,Nataša Šijaković Vujičić,Ivo Crnolatac,Marcin Górecki

doi:10.3390/md17110629

Abstract

We demonstrated the hitherto unknown property of the mycotoxin sterigmatocystin (STC) to provide homogeneous solutions in aqueous medium by forming a unique aggregate type (not formed by analogous aflatoxins), characterized by exceptionally strong circular dichroism (CD) bands in the 300–400 nm range. Results showed that these CD bands do not originate from intrinsic STC chirality but are a specific property of a peculiar aggregation process similar to psi-DNA CD response. Transmission electron microscopy (TEM) experiments revealed a fine fiber network resembling a supramolecular gel structure with helical fibers. Thermodynamic studies of aggregates by differential scanning calorimetry (DSC) revealed high reversibility of the dominant aggregation process. We demonstrated that the novel STC psi-CD band at 345 nm could be applied at biorelevant conditions (100 nanomolar concentration) and even in marine-salt content conditions for specific and quantitative monitoring of STC. Also, we showed that STC strongly non-covalently interacts with ds-DNA with likely toxic effects, thus contrary to the previous belief requiring prior enzyme epoxidation.

Highlights

IntroductionNon-charged aromatic molecules are commonly considered insoluble in water
Large, non-charged aromatic molecules are commonly considered insoluble in water
Motivated by uniquely strong circular dichroism (CD) response to STC aggregation, as well as the applicability of these results in sensitive and specific mycotoxin detection, we studied in detail the STC aggregation in biorelevant conditions

Summary

Introduction

Non-charged aromatic molecules are commonly considered insoluble in water. It is well-known that many of these systems are strongly hydrophobic and tend to form aggregates and crystals based on π-stacking and dispersive interactions. If a concentrated stock solution of a large aromatic molecule is prepared in an organic solvent miscible with water, and a small aliquot is added to large bulk water, instant precipitation does not happen. A more or less stable homogeneous equilibrium state is formed, like in colloids or micelle-like constructs. In biological systems some naturally occurring large aromatic molecules play an important role, for instance, the family of aflatoxin-related mycotoxins [1] consists of several condensed aromatic systems (Scheme 1). Being non-charged, most of them possess moieties (e.g., hydroxyl) with latent

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Conclusion