The production of nanoparticles (NPs) is increasing rapidly for applications in electronics, chemistry, and biology. This interest is due to the very small size of NPs which provides them with many interesting properties such as rapid diffusion, high specific surface areas, reactivity in liquid or gas phase, and a size close to biomacromolecules. In turn, these extreme abilities might be a problem when considering a potentially uncontrolled exposure to the environment. For instance, nanoparticles might be highly mobile and rapidly transported in the environment or inside the body through a water or air pathway. Accordingly, the very fast development of these new synthetic nanomaterials raises questions about their impact on the environment and human health. We have studied the impact of a model water dispersion of nanoparticles (7 nm CeO2 oxide) on a Gram-negative bacteria (Escherichia coli). The nanoparticles are positively charged at neutral pH and thus display a strong electrostatic attraction toward bacterial outer membranes. The counting of colony forming units (CFU) after direct contact with CeO2 NPs allows for the defining of the conditions for which the contact is lethal to Escherichia coli. Furthermore, a set of experiments including sorption isotherms, TEM microscopy, and X-ray absorption spectroscopy (XAS) at cerium L3 edge is linked to propose a scenario for the observed toxic contact.

Glutaredoxins (GRX) are redox proteins which use glutathione as a cofactor and are divided into two classes, monothiol and dithiol. In each class, several GRX have been shown to form [Fe2S2] cluster coordinating homodimers. The dithiol GRX homodimer is proposed to serve as a sequestration form and its iron-sulfur cluster as an oxidative stress sensor. In contrast, the monothiol GRX homodimer has been suggested to act as a scaffold for [Fe2S2] cluster delivery. We present here the structure of a monothiol GRX homodimer (Escherichia coli GRX4) coordinating a [Fe2S2] cluster that reveals the structural basis of intact iron-sulfur cluster delivery.