Exploiting Peptidomimetics to Synthesize Compounds That Activate Ryanodine Receptor Calcium Release Channels

A Water Soluble Pd2 L4 Cage for Selective Binding of Neu5Ac

The sialic acid N-acetylneuraminic acid (Neu5Ac) and its derivatives are involved in many biological processes including cell-cell recognition and infection by influenza. Molecules that can recognize Neu5Ac might thus be exploited to intervene in or monitor such events. A key obstacle in this development is the sparse availability of easily prepared molecules that bind to this carbohydrate in its natural solvent; water. Here, we report that the carbohydrate binding pocket of an organic soluble [Pd2 L4 ]4+ cage could be equipped with guanidinium-terminating dendrons to give the water soluble [Pd2 L4 ][NO3 ]16 cage 7. It was shown by means of NMR spectroscopy that 7 binds selectively to anionic monosaccharides and strongest to Neu5Ac with Ka =24 M-1 . The cage had low to no affinity for the thirteen neutral saccharides studied. Aided by molecular modeling, the selectivity for anionic carbohydrates such as Neu5Ac could be rationalized by the presence of charge assisted hydrogen bonds and/or the presence of a salt bridge with a guanidinium solubilizing arm of 7. Establishing that a simple coordination cage such as 7 can already selectively bind to Neu5Ac in water paves the way to improve the stability, affinity and/or selectivity properties of M2 L4 cages for carbohydrates and other small molecules.

A Synthetic Galectin Mimic

Galectins are a galactoside specific subclass of carbohydrate binding proteins (lectins) involved in various cellular activities, certain cancers, infections, inflammations, and many other biological processes. The molecular basis for the selectivity of galectins is well-documented and revolves around appropriate interaction complementarity: an aromatic residue for C-H⋅⋅⋅π interactions and polar residues for (charge assisted) hydrogen bonds with the axial hydroxyl group of a galactoside. However, no synthetic mimics are currently available. We now report on the design and synthesis of the first galectin mimic (6), and show that it has a higher than 65-fold preference for n-octyl-β-galactoside (8) over n-octyl-β-glucoside (7) in CD2 Cl2 containing 5 % [D6 ]DMSO (with Ka ≥4500 M-1 for 6:8). Molecular modeling informed by nOe studies reveal a high degree of interaction complementarity between 6 and galactoside 8, which is very similar to the interaction complementarity found in natural galectins.

Peptide mimetic compounds can activate or inhibit cardiac and skeletal ryanodine receptors

AIMS

Our aim was to characterise the actions of novel BIT compounds with structures based on peptides and toxins that bind to significant regulatory sites on ryanodine receptor (RyR) Ca²⁺ release channels. RyRs, located in sarcoplasmic reticulum (SR) Ca²⁺ store membranes of striated muscle, are essential for muscle contraction. Although severe sometimes-deadly myopathies occur when the channels become hyperactive following genetic or acquired changes, specific inhibitors of RyRs are rare.

MAIN METHODS

The effect of BIT compounds was determined by spectrophotometric analysis of Ca²⁺ release from isolated SR vesicles, analysis of single RyR channel activity in artificial lipid bilayers and contraction of intact and skinned skeletal muscle fibres.

KEY FINDINGS

The inhibitory compounds reduced: (a) Ca²⁺ release from SR vesicles with IC50s of 1.1-2.5 μM, competing with activation by parent peptides and toxins; (b) single RyR ion channel activity with IC50s of 0.5-1.5 μM; (c) skinned fibre contraction. In contrast, activating BIT compounds increased Ca²⁺ release with an IC50 of 5.0 μM and channel activity with AC50s of 2 to 12 nM and enhanced skinned fibre contraction. Sub-conductance activity dominated channel activity with both inhibitors and activators. Effects of all compounds on skeletal and cardiac RyRs were similar and reversible. Competition experiments suggest that the BIT compounds bind to the regulatory helical domains of the RyRs that impact on channel gating mechanisms through long-range allosteric interactions.

SIGNIFICANCE

The BIT compounds are strong modulators of RyR activity and provide structural templates for novel research tools and drugs to combat muscle disease.

Supramolecular microtubes based on 1,3,5-benzenetricarboxamides prepared by self-assembly upon heating

A series of three 1,3,5-benzenetricarboxamides with peripheral tertiary N,N-dialkyl-ethylamino substituents with different length of the alkyl groups is reported. In particular, the N¹,N³,N⁵-tris[2-(diethylamino)-ethyl]-1,3,5-benzenetricarboxamide exhibits phase separation followed by self-assembly upon heating from aqueous solution into well-defined supramolecular fiber-like structures in the form of microtubes.

Novel anti-Alzheimer phenol-lipoyl hybrids: Synthesis, physico-chemical characterization, and biological evaluation

To date, drugs that hit a single target are inadequate for the treatment of neurodegenerative diseases, such as Alzheimer's or Parkinson's diseases. The development of multitarget ligands, able to interact with the different pathways involved in the progession of these disorders, represents a great challenge for medicinal chemists. In this context, we report here the synthesis and biological evaluation of phenol-lipoyl hybrids (SV1-13), obtained via a linking strategy, to take advantage of the synergistic effect due to the antioxidant portions and anti-amyloid properties of the single constituents present in the hybrid molecule. Biological results showed that SV5 and SV10 possessed the best protective activity against Aβ_1-42 induced neurotoxicity in differentiated SH-SY5Y cells. SV9 and SV10 showed remarkable antioxidant properties due to their ability to counteract the damage caused by H₂O₂ in SHSY-5Y-treated cells. Hovewer, SV5, showing moderate antioxidant and good neuroprotective activities, resulted the best candidate for further experiments since it also resulted stable both simulated and plasma fluids.

Therapeutic implications of novel peptides targeting ER-mitochondria Ca2+-flux systems

Intracellular Ca²⁺-flux systems located at the ER-mitochondrial axis govern mitochondrial Ca²⁺ balance and cell fate. Multiple yet incurable pathologies are characterized by insufficient or excessive Ca²⁺ fluxes toward the mitochondria, in turn leading to aberrant cell life or death dynamics. The discovery and ongoing molecular characterization of the main interorganellar Ca²⁺ gateways have resulted in a novel class of peptide tools able to regulate relevant protein-protein interactions (PPIs) underlying this signaling scenario. Here, we review peptides, molecularly derived from Ca²⁺-flux systems or their accessory proteins. We discuss how they alter Ca²⁺-signaling protein complexes and modulate cell survival in light of their forthcoming therapeutic applications.