Calcium-sensing receptor in GtoPdb v.2021.3

The calcium-sensing receptor (CaS, provisional nomenclature as recommended by NC-IUPHAR [47] and subsequently updated [77]) responds to multiple endogenous ligands, including extracellular calcium and other divalent/trivalent cations, polyamines and polycationic peptides, L-amino acids (particularly L-Trp and L-Phe), glutathione and various peptide analogues, ionic strength and extracellular pH (reviewed in [78]). While divalent/trivalent cations, polyamines and polycations are CaS receptor agonists [14, 110], L-amino acids, glutamyl peptides, ionic strength and pH are allosteric modulators of agonist function [36, 47, 61, 108, 109]. Indeed, L-amino acids have been identified as "co-agonists", with both concomitant calcium and L-amino acid binding required for full receptor activation [148, 54]. The sensitivity of the CaS receptor to primary agonists is increased by elevated extracellular pH [18] or decreased extracellular ionic strength [109]. This receptor bears no sequence or structural relation to the plant calcium receptor, also called CaS.

Peptoids with Antibiofilm Activity against the Gram Negative Obligate Anaerobe, Fusobacterium nucleatum

Peptoids (oligo N-substituted glycines) are peptide analogues, which can be designed to mimic host antimicrobial peptides, with the advantage that they are resistant to proteolytic degradation. Few studies on the antimicrobial efficacy of peptoids have focused on Gram negative anaerobic microbes associated with clinical infections, which are commonly recalcitrant to antibiotic treatment. We therefore studied the cytotoxicity and antibiofilm activity of a family of peptoids against the Gram negative obligate anaerobe Fusobacterium nucleatum, which is associated with infections in the oral cavity. Two peptoids, peptoid 4 (NaeNpheNphe)4 and peptoid 9 (NahNspeNspe)3 were shown to be efficacious against F. nucleatum biofilms at a concentration of 1 μM. At this concentration, peptoids 4 and 9 were not cytotoxic to human erythrocytes or primary human gingival fibroblast cells. Peptoids 4 and 9 therefore have merit as future therapeutics for the treatment of oral infections.

A Cyclic BMP-2 Peptide Upregulates BMP-2 Protein-Induced Cell Signaling in Myogenic Cells

In the current study, we designed four cyclic peptide analogues by incorporating two cysteine residues in a BMP-2 linear knuckle epitope in such a way that the active region of the peptide could be either inside or outside the cyclic ring. Bone morphogenetic protein receptor BMPRII was immobilized on the chip surface, and the interaction of the linear and cyclic peptide analogues was studied using surface plasmon resonance (SPR). From the affinity data, the peptides with an active region inside the cyclic ring had a higher binding affinity in comparison to the other peptides. To confirm that our affinity data are in line in vitro, we studied the expression levels of RUNX2 (runt-related transcription factor) and conducted an osteogenic marker alkaline phosphatase (ALP) assay and staining. Based on the affinity data and the in vitro experiments, peptide P-05 could be a suitable candidate for osteogenesis, with higher binding affinity and increased RUNX2 and ALP expression in comparison to the linear peptides.

Clusterin in Alzheimer’s Disease: An Amyloidogenic Inhibitor of Amyloid Formation

Background: Clusterin is a heterodimeric glycoprotein (α- and β-chain), which has been described as an extracellular molecular chaperone. In humans, clusterin is an amyloid associated protein, co-localizing with fibrillar deposits in Alzheimer’s disease. To clarify its implication in the disease, we provide evidence that clusterin has intrinsic amyloidogenic properties, which are intertwined with its inhibitory effect on amyloid-β fibril formation.Methods: Aggregation-prone regions of human clusterin were predicted by AMYLPRED. Synthetic peptide-analogues of each region underwent in vitro aggregation assays, namely, examination with transmission electron microscopy, X-Ray diffraction from oriented fibers, ATR FT-IR spectroscopy, and Congo Red birefringence assays. The same peptide-analogues were co-incubated with amyloid-β and their potential as inhibitors was tested with thioflavin T fluorescence emission measurements and transmission electron microscopy. Molecular dynamics simulations were performed to gain insight into the interaction between amyloid-β and the peptide-analogues.Results: Clusterin peptide-analogues form amyloid-like fibrils, as revealed by transmission electron microscopy. They can form fibers that give cross-β X-ray diffraction patterns and ATR FT-IR spectroscopy confirms the dominance of β-strand secondary structure. They also exhibit apple-green birefringence, when stained with Congo Red and examined between crossed polars of a polarizing light microscope. Furthermore, when amyloid-β is co-incubated with clusterin’s peptide analogues, it shows decreased thioflavin T fluorescence emission over time, while the formation of amyloid-β amyloid fibrils is diminished, as confirmed by transmission electron microscopy. The inhibitory effect of clusterin-peptide analogues on amyloid-β fibril formation was ascertained though molecular dynamics simulations. Conclusions: Clusterin has multiple aggregation-prone regions in its α-chain and these regions have a functional role in the inhibition of amyloid-β fibril formation.

Clusterin in Alzheimer's disease: an amyloidogenic inhibitor of amyloid formation

Clusterin is a heterodimeric glycoprotein (alpha- and beta-chain), which has been described as an extracellular molecular chaperone. In humans, clusterin is an amyloid associated protein, co-localizing with fibrillar deposits in several amyloidoses, including Alzheimer's disease. To clarify its potential implication in amyloid formation, we located aggregation-prone regions within the sequence of clusterin a-chain, via computational methods. We had peptide-analogues of each region chemically synthesized and experimentally demonstrated that all of them can form amyloid-like fibrils. We also provide evidence that the same peptide-analogues can inhibit amyloid-beta fibril formation. These findings elucidate parts of the molecular mechanism in which clusterin inhibits amyloid formation. At the same time, they hint that molecular chaperones with amyloidogenic properties might have a role in the regulation of amyloid formation, essentially acting as functional amyloids.

Cationicity and hydrophobicity enhance the cytotoxic potency of Phoratoxin C anticancer peptide analogues against triple negative breast cancer cells

Background: Anticancer peptides (ACPs) have received increasing attention as a promising class of novel anticancer agents owing to its potent and rapid cytotoxic properties. In this study, we aim to investigate the effects of cationicity and hydrophobicity in modulating the cytotoxicity of PtxC, a class of ACP from the leafy mistletoe Phoradendron tomentosum against the MDA-MB-231 and Vero cells. Method: We designed a series of four PtxC analogues (PA1 – PA4) by residual substitutions with specific amino acids to introduce the specific charge and hydrophobicity alterations to the analogues. The cytotoxicity strength of the PtxC analogues on MDA-MB-231 and Vero cells were tested by using MTT assay at 24 hours post treatment. Results: PA1, PA2 and PA4 displayed marked increases in cytotoxicity against both MDA-MB-231 and Vero cells and can be ranked in the order of PA2 > PA4 > PA1 > PtxC > PA3. Sequence-activity relationship analyses of the designed analogues showed that an increase in the level of cationicity and hydrophobicity correlated well with the enhanced cytotoxic activity of PtxC analogues. This was observed with PA1 (netC +8) and PA2 (netC +10) in comparison to PtxC (netC +7). Similar finding was observed for PA4 (GRAVY +0.070) in contrast to PtxC (GRAVY -0.339). Three-dimensional modelling predicted a double α-helix structure in PtxC class of ACP. The larger first helix in PA2 and PA4 was suggested to be responsible for the enhanced cytotoxicity observed. Conclusion: The critical role of cationicity and hydrophobicity in enhancing cytotoxicity of PtxC class of ACPs were clearly demonstrated in our study. The current findings could be extrapolated to benefit peptide design strategy in other classes of ACPs toward the discovery of highly potent ACPs against cancer cells as potential novel therapeutic agents.