Abstract
Cells have evolved sophisticated molecular control systems to maximize the efficiency of the folding process. However, any subtle alteration of the environment or the protein can lead to misfolding or affect the conformational plasticity of the native states. It has been widely demonstrated that misfolding and/or conformational instability are the underlying mechanisms of several rare disorders caused by enzymatic deficits. In fact, disease-causing mutations often lead to the substitution of amino acids that are crucial for the achievement of a folded conformation, or play a role on the equilibrium between native-state conformers. One of the promising approaches to treat conformational disorders is the use of pharmacological chaperones (PCs), small molecules that specifically bind a target protein and stabilize a functional fold, thus increasing the amount of functionally active enzyme. Molecules acting as PCs are usually coenzymes, substrate analogues behaving as competitive inhibitors, or allosteric modulators. In this review, the general features of PCs are described, along with three examples of diseases (Gaucher disease, Phenylketonuria, and Primary Hyperoxaluria) in which this approach is currently under study at preclinical and/or clinical level.
Highlights
Most studies on the folding pathway of globular proteins have been guided by two paradigms: (1) the polypeptide chain follows its route in a folding funnel leading to a unique native structure, which represents the most stable conformation under physiological conditions. (2) the major driving force for folding is the “hydrophobic burst”, i.e., the interaction between residues showing hydrophobic side chains
The global picture of the protein folding process should consider that the events occurring in a cell may differ from those occurring in vitro in many respects including: (i) the vectorial protein synthesis, which allows cotranslational folding to occur. (ii) the presence of a crowded environment, which can promote aggregation. (iii) the influence of subcellular import, which can occur on the unfolded or the folded state depending on the organelle, and of binding partners, that can promote correct folding. (iv) the action of various classes of molecular chaperones, proteins that use the free energy of ATP hydrolysis to help the folding process by inhibiting or reverting aggregation, promoting the achievement of the native conformation, and/or allowing the degradation of misfolded intermediates [31,32,33,34,35]
We focused this review on three examples of rare diseases due to enzymatic deficits for which a therapy with molecules acting as pharmacological chaperone (PC) has been investigated
Summary
The global processes of synthesis, recycling, modification, or degradation of the proteome of a cell are governed by molecular complexes that are involved into protein homeostasis regulation (proteostasis) [36]. The loss-of-function is caused by the absence of an adequate amount of an otherwise catalytically-active variant, due to a conformational defect that can promote intracellular aggregation, increased degradation, aberrant subcellular localization, or an aberrant regulation hampering the conversion into active states [34, 45] Upon this discovery, many efforts have been dedicated to the identification of strategies able to rescue for the effects of destabilizing mutations leading to misfolding. In proteins showing significant structural plasticity in the native state, PCs can influence the equilibrium among the different possible conformers, e.g., stabilizing the more active and/or stable one under physiological conditions, possibly through a mechanism of conformational selection as proposed in the case of molecular chaperones [67] Their action is protein and mutationspecific, different studies demonstrate that they can be efficacious for more than 50% of missense mutations [68]. Primary Hyperoxaluria Type I is a disease in which both coenzymatic forms and substrate analogues have been tested for their chaperone activity
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