Transporters of the amino acid, polyamine and organocation (APC) superfamily play essential roles in cell redox balance, cancer, and aminoacidurias. The bacterial L-arginine/agmatine antiporter, AdiC, is the main APC structural paradigm and shares the “5 + 5 inverted repeat” fold found in other families like the Na + -coupled neurotransmitter transporters. The available AdiC crystal structures capture two states of its transport cycle: the open-to-out apo and the outward-facing Arg + -bound occluded. However, the role of Arg + during the transition between these two states remains unknown. Here, we report the crystal structure at 3.0 Å resolution of an Arg + -bound AdiC mutant (N101A) in the open-to-out conformation, completing the picture of the major conformational states during the transport cycle of the 5 + 5 inverted repeat fold-transporters. The N101A structure is an intermediate state between the previous known AdiC conformations. The Arg + -guanidinium group in the current structure presents high mobility and delocalization, hampering substrate occlusion and resulting in a low translocation rate. Further analysis supports that proper coordination of this group with residues Asn101 and Trp293 is required to transit to the occluded state, providing the first clues on the molecular mechanism of substrate-induced fit in a 5 + 5 inverted repeat fold-transporter. The pseudosymmetry found between repeats in AdiC, and in all fold-related transporters, restraints the conformational changes, in particular the transmembrane helices rearrangements, which occur during the transport cycle. In AdiC these movements take place away from the dimer interface, explaining the independent functioning of each subunit.

Molecular chaperones HSP90 and HSP70 are essential regulators of the folding and activation of a disparate ensemble of client proteins. They function through ATP hydrolysis and the assembly of multiprotein complexes with cochaperones and clients. While their therapeutic relevance is recognized, important details underlying the links between ATP-dependent conformational dynamics and clients/cochaperones recruitment remain elusive. Allosteric modulators represent fundamental tools to obtain molecular insights into functional regulation. By selective perturbation of different aspects of HSP90/HSP70 activities, allosteric drugs can tune rather than completely inhibit signaling cascades, providing information on the relationships between structure-dynamics and function. Herein, we review advances in the design of HSP90 and HSP70 allosteric modulators. We consider inhibitors and activators in different biochemical and disease models. We discuss these compounds as probes to decipher the complexity of the chaperone machinery and that at the same time represent starting leads for the development of drugs against cancer and neurodegeneration.

Nine genetically inherited neurodegenerative diseases are linked to abnormal expansions of a polyglutamine (polyQ) encoding region. Over the years, several structural models for polyQ regions have been proposed and confuted. The cross-beta-spine steric zipper motif, identified recently for the GNNQQNY peptide, represents an attractive model for amyloid fibers formed by polyQ fragments. Here we report a detailed molecular dynamics investigation of polyQ models assembled by cross-beta-spine steric zipper motifs. Our simulations indicate clearly that these assemblies are very stable. Glutamine side chains contribute strongly to the overall stability of the models by fitting perfectly within the zipper. In contrast to GNNQQNY zipper motifs, hydrogen bonding interactions provide a significant contribution to the overall stability of polyQ models. Molecular dynamics simulations carried out on monomeric polyQ forms (composed by 40-60 residues) show clearly that they can also assume structures stabilized by steric zipper motifs. Based on these findings, we build monomeric polyQ models that can explain recent data on the toxicity exerted by these species. In a more general context, our data suggests that polyQ models with interdigitated side chains can provide a structural rationale to several literature experiments on polyQ formation, stability, and toxicity.

No abstract

Schistosomiasis is the most significant neglected tropical parasitic disease caused by helminths in terms of morbidity and mortality caused by helminths. In this work, we present the antischistosomal activity against Schistosoma mansoni of a rationally selected small set of thiazinoquinone derivatives, some of which were previously found to be active against Plasmodium falciparum and others synthesized ad hoc. The effects on larvae, juvenile, and adult parasite viability as well as on egg production and development were investigated, resulting in the identification of new multistage antischistosomal hit compounds. The most promising compounds 6, 8, 13, and 14 with a LC 50 value on schistosomula from ∼5 to ∼15 μM also induced complete death of juvenile (28 days old) and adult worm pairs (7 weeks old) and a detrimental effect on egg production and development in vitro. Structure−activity relationships (SARs) were analyzed by means of computational studies leading to the hypothesis of a redox-based mechanism of action with a one-electron reduction bioactivation step and the subsequent formation of a toxic semiquinone species, similarly to what was previously observed for the antiplasmodial activity. Our results also evidenced that the selective toxicity against mammalian cells or parasites as well as specific developmental stages of a parasite can be addressed by varying the nature of the introduced substituents.

No abstract

Sirt-1 is defined as a nuclear protein involved in the molecular mechanisms of inflammation and neurodegeneration through the de-acetylation of many different substrates even if experimental data in mouse suggest both its cytoplasmatic presence and nucleo-cytoplasmic shuttling upon oxidative stress. Since the experimental structure of human Sirt-1 has not yet been reported, we have modeled its 3D structure, highlighted that it is composed by four different structural regions: N-terminal region, allosteric site, catalytic core and C-terminal region, and underlined that the two terminal regions have high intrinsic disorder propensity and numerous putative phosphorylation sites. Many different papers report experimental studies related to its functional activators because Sirt-1 is implicated in various diseases and cancers. The aim of this article is (i) to present interactomic studies based human Sirt-1 to understand its most important functional relationships in the light of the gene–protein interactions that control major metabolic pathways and (ii) to show by docking studies how this protein binds some activator molecules in order to evidence structural determinants, physico-chemical features and those residues involved in the formation of complexes.

Veronesi, Marina et al. (2020) Chemical perturbation of oncogenic protein folding: from the prediction of locally unstable structures to the design of disruptors of Hsp90-Client interactions. Chemistry -A European Journal, 26 (43). pp. 9459-9465.