Total Synthesis and Structural Characterization of Caveolin-1.

Caveolin-1, which is an essential protein for caveola formation, was chemically synthesized. It is composed of 177 amino acid residues, is triply palmitoylated at the C-terminal region, and is inserted into the lipid bilayer to form a V-shaped structure in the middle of the polypeptide chain. The entire sequence was divided into five peptide segments, each of which was synthesized by the solid-phase method. To improve the solubility of the C-terminal region, O-acyl isopeptide structures were incorporated. After ligation by the thioester method and the introduction of the palmitoyl groups, all the protecting groups were removed and the isopeptide structures were converted into the native peptide bond. Finally, the obtained polypeptide was successfully inserted into bicelles, thus showing the success of the synthesis.

An Aß42 uptake and degradation via Rg3 requires an activation of caveolin, clathrin and Aß-degrading enzymes in microglia.

We demonstrated previously that ginsenoside Rg3 enhances the expression of macrophage scavenger receptor class A (SRA) and amyloid ß peptide 1-42 (Aß42) uptake in BV2 cells. In this study, we investigated the biochemical and mechanistic roles of Rg3 in human microglia and animal models to identify the determinants that participate in restoring memory and learning in brains disrupted by the Aß42 peptide. SRA was expressed highly in Rg3-treated rats, and learning and memory functions were maintained at a normal level after the infusion of Aß42. SRA-transfected HMO6 human microglial cells (HMO6.hSRA) overexpressed SRA and took up a remarkable amount of Aß42. Rg3-treated HMO6 cells showed highly enhanced SRA expression and dramatically promoted Aß42 uptake. Moreover, high levels of clathrin and caveolin1 supported the roles of Rg3 in endocytic biogenesis by activating p38 and extracellular signal-regulated protein kinase signaling. Notably, both neprilysin (NEP) and insulin-degrading enzyme (IDE) were significantly expressed by Rg3, suggesting independent and compensatory hydrolytic activity for the Aß peptide. In conclusion, Rg3 successfully triggered Aß42 uptake via SRA and clathrin-/caveolae-mediated endocytic mechanisms and further contributed to accelerate the degradation of Aß peptide via the increase of intracellular NEP and IDE, which may be a promising Alzheimer׳s disease therapy.

Slightly modifying pseudoproline dipeptides incorporation strategy enables solid phase synthesis of a 54 AA fragment of caveolin-1 encompassing the intramembrane domain.

This work contributes to highlight the benefits of pseudoproline dipeptides introduction in difficult SPPS. We show how a slight modification in the positioning choice conditioned the synthesis achievement of a 54 amino acid long caveolin-1 peptide encompassing the intramembrane domain. Furthermore, we report a side reaction correlated with the coupling steps and generating truncated fragments with a mass deviation of + 42 Da. Considering the need of structural data for membrane proteins, most of which are considered as prevalent therapeutic targets, chemical synthesis provides an interesting alternative pathway to obtain hydrophobic domains by pushing back the frontiers of conventional RP methods of purification.