Developing a compound-specific receptor for bisphenol a by directed evolution of human estrogen receptor α

Rewiring Estrogen Receptor α into Bisphenol Selective Receptors Using Darwin Assembly-Based Directed Evolution (DADE) in Saccharomyces cerevisiae

Bisphenols are widely used in manufacturing plastics and resins, but their environmental persistence raises concerns to human health and ecosystems. Accurate measurements for bisphenols are crucial for effective monitoring and regulation. Analytical methods detect only preselected bisphenols, while bioassays assessing estrogen receptor α activation suffer from poor sensitivity and strong background signals due to estrogenic contaminations. To develop a bioassay in Saccharomyces cerevisiae with increased sensitivity and specificity for bisphenols, we performed multi-site directed mutagenesis and directed evolution of more than 108 stably integrated estrogen receptor variants. By mutating the estrogen receptor α towards recognition of bisphenol A in yeast, we determined the preBASE variant (M421G_V422G_V533D_L536G_Y537S) with elevated bisphenol A sensitivity (EC50:329 nM) and lost estrogen responsiveness (EC50:0,17 mM). Further engineering yielded an off-target mutant, identified as the Bisphenol-Affinity and Specificity-Enhanced (BASE) variant (M421G_V422G_V533D_L536G_Y537S_L544I) that uses bisphenols as its primary agonist (EC50:32 mM) and impaired estrogen sensitivity (EC50:85M). The rewiring into a bisphenol receptor was confirmed in ligand binding assays to purified ligand binding domains. Taken together, the identified variants form stepping stones for further protein engineering to generate bisphenol specific high-throughput yeast-based bioassays.

Shining light on molecular communication

Molecules and combinations of molecules are the natural communication currency of microbes; microbes have evolved and been engineered to sense a variety of compounds, often with exquisite sensitivity. The availability of microbial biosensors, combined with the ability to genetically engineer biological circuits to process information, make microbes attractive bionanomachines for propagating information through molecular communication (MC) networks. However, MC networks built entirely of biological components suffer a number of limitations. They are extremely slow due to processing and propagation delays and must employ simple algorithms due to the still limited computational capabilities of biological circuits. In this work, we propose a hybrid bio-electronic framework which utilizes biological components for sensing but offloads processing and computation to traditional electronic systems and communication infrastructure. This is achieved by using tools from the burgeoning field of optogenetics to trigger biosensing through an optoelectronic interface, alleviating the need for computation and communication in the biological domain.

Yeast-Based Biosensors: Current Applications and New Developments

Biosensors are regarded as a powerful tool to detect and monitor environmental contaminants, toxins, and, more generally, organic or chemical markers of potential threats to human health. They are basically composed of a sensor part made up of either live cells or biological active molecules coupled to a transducer/reporter technological element. Whole-cells biosensors may be based on animal tissues, bacteria, or eukaryotic microorganisms such as yeasts and microalgae. Although very resistant to adverse environmental conditions, yeasts can sense and respond to a wide variety of stimuli. As eukaryotes, they also constitute excellent cellular models to detect chemicals and organic contaminants that are harmful to animals. For these reasons, combined with their ease of culture and genetic modification, yeasts have been commonly used as biological elements of biosensors since the 1970s. This review aims first at giving a survey on the different types of yeast-based biosensors developed for the environmental and medical domains. We then present the technological developments currently undertaken by academic and corporate scientists to further drive yeasts biosensors into a new era where the biological element is optimized in a tailor-made fashion by in silico design and where the output signals can be recorded or followed on a smartphone.

Drinking water contaminants from epoxy resin-coated pipes: A field study

Rehabilitation of aged drinking water pipes is an extensive renovation and increasingly topical in many European cities. Spray-on-lining of drinking water pipes is an alternative cost-effective rehabilitation technology in which the insides of pipes are relined with organic polymer. A commonly used polymer is epoxy resin consisting of monomer bisphenol A (BPA). Leaching of BPA from epoxy lining to drinking water has been a concern among public and authorities. Currently epoxy lining is not recommended in some countries. BPA leaching has been demonstrated in laboratory studies but the behavior and ageing process of epoxy lining in situ is not well known. In this study 6 locations with different age epoxy linings of drinking water pipes done using two distinct technologies were studied. While bisphenol F, 4-n-nonylphenol, and 4-t-octylphenol were rarely found and in trace concentrations, BPA was detected in majority of samples. Pipes lined with the older technology (LSE) leached more BPA than those with more recent technology (DonPro): maxima in cold water were 0.25 μg/L and 10 ng/L, respectively. Incubation of water in pipes 8-10 h prior to sampling increased BPA concentration in cold water 1.1-43-fold. Hot water temperature caused even more BPA leaching - at maximum 23.5 μg/L. The influence of ageing of epoxy lining on BPA leaching on could be shown in case of LSE technology: locations with 8-9 years old lining leached 4-20-fold more BPA compared to a location with 2-year-old lining. Analysis of metals showed that epoxy lining can reduce especially iron concentration in water. No significant burden to water could be shown by the analyzed 72 volatile organic compounds, including epichlorhydrin, precursor used in epoxy resin. Estrogenicity was detected in water samples with the highest BPA loads. Comparable responses of two yeast bioreporters (estrogen receptor α and BPA-targeted) indicated that bisphenol-like compounds were the main cause of estrogenicity. Compared to the estimated average daily BPA exposure, additional BPA load via cold drinking water in the studied locations was low, maximum 8.7%. However, hot water should also be considered as exposure source due to higher BPA concentrations. Epoxy lined locations should be monitored in future in order to evaluate ageing process and control increasing leaching of potentially harmful chemicals.