The morphology of non-functionalized gold nanostars determines the surface protein structure and their interaction with the endolysosomal compartment in cells.

Here we investigated the effect of electrostatic interactions and of protein tyrosine nitration of mammalian cytochrome c on the dynamics of the so-called alkaline transition, a pH-and redoxtriggered conformational change that implies replacement of the axial ligand Met80 by a Lys residue. Using a combination of electrochemical, time-resolved SERR spectroelectrochemical experiments and molecular dynamics simulations we showed that in all cases the reaction can be described in terms of a two steps minimal reaction mechanism consisting of deprotonation of a triggering group followed by ligand exchange. The pK a alk values of the transition are strongly modulated by these perturbations, with a drastic downshift upon nitration and an important upshift upon establishing electrostatic interactions with a negatively charged model surface. The value of pK a alk is determined by the interplay between the acidity of a triggering group and the kinetic constants for the forward and backward ligand exchange processes. Nitration of Tyr74 results in a change of the triggering group from Lys73 in WT Cyt to Tyr74 in the nitrated protein, which dominates the pK a alk downshift towards physiological values. Electrostatic interactions, on the other hand, result in strong acceleration of the backward ligand exchange reaction, which dominates the pK a alk upshift. The different physicochemical conditions found here to influence pK a alk are expected to vary depending on cellular conditions and subcellular localization of the protein, thus determining the existence of alternative conformations of Cyt in vivo.

Understanding the formation of the intracellular protein corona of nanoparticles is essential for a wide range of bio- and nanomedical applications. The innermost layer of the protein corona, the hard...

Synthetic cytocompatible CeO 2 nanoparticles embedded in transparent silica hydrogels are useful for creating inorganic supports favoring the long-term entrapment of living Chlorella vulgaris cells. The key protective role of nanoparticles is twofold: (1) They efficiently absorb harmful UV radiation without scattering the useful visible one. (2) They limit oxidative stress damage, such as that induced by H 2 O 2 , thanks to the surface redox Ce 3þ -Ce 4þ reactivity of nanoparticles.

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International audienceAs an alternative approach to the well known Ca(II)-alginate encapsulation process within silica hydrogels, proton-driven alginate gelation was investigated in order to establish its capacity as a culture carrier, both isolated and embedded in an inorganic matrix. Control over the velocity of the proton-gelation front allows the formation of a hydrogel shell while the core remains liquid, allowing bacteria and microalgae to survive the strongly acidic encapsulation process. Once inside the inorganic host, synthesized by a sol-gel process, the capsules spontaneously redissolve without the aid of external complexing agents. The entrapped cells survive the two-step process to a significant extent; culture's growth restores the initial cell count in less than two weeks. Biosynthesis of Au nanoparticles mediated by the entrapped microalgae illustrates the preservation of the biosynthetic abilities supported by this platform