Preparation and Characterization of a Phospholipid Membrane-Bound Tetrapeptide That Corresponds to the C-Terminus of the Gastrin/Cholecystokinin Hormone Family

Magnetoliposomes: versatile innovative nanocolloids for use in biotechnology and biomedicine

The high biocompatibility and versatile nature of liposomes have made these particles keystone components in many hot-topic biomedical research areas. Liposomes can be combined with a large variety of nanomaterials, such as superparamagnetic iron oxide nanocores. Because the unique features of both the magnetizable colloid and the versatile lipid bilayer can be joined, the resulting so-called magnetoliposomes can be exploited in a great array of biotechnological and biomedical applications. In this article, we highlight the use of magnetoliposomes in immobilizing enzymes, both water-soluble and hydrophobic ones, as well as their potential in several biomedical applications, including MRI, hyperthermia cancer treatment and drug delivery. The goal of this article is not to list all known uses of magnetoliposomes but rather to present some conspicuous applications in comparison to other currently used nanoparticles.

Evidence for a C-terminal structural motif in gastrin and its bioactive fragments in membrane mimetic media

The conformational preferences of human little gastrin, [Nle(15)] gastrin-17, and its short analogues, gastrin-4 and [beta-Ala(1)] gastrin-5, which include the C-terminal tetrapeptide sequence Trp-Met-Asp-Phe-NH(2) crucial for gastrin bioactivity, were determined by NMR spectroscopy in aqueous solutions of zwitterionic dodecylphosphocholine micelles. Backbone HN chemical shift temperature variance, Halpha chemical shift deviations and complex non-sequential NOE patterns pointed to the C-terminal of [Nle(15)] gastrin-17 adopting an ordered conformation. Distance geometry calculations and NOE-restrained molecular dynamics simulations in membrane mimetic solvent boxes of decane and water indicated the C-terminal tetrapeptide sequence of all three peptides adopted a similar, well defined structure, with a general type IV beta-turn observed for all three peptides. The conformation of [Nle(15)] gastrin-17 consisted of two short helices between Leu(5)-Glu(9) and Ala(11)-Trp(14), with the one helix terminating in a type I beta-turn spanning Gly(13)-Asp(16). The experimental evidence and conformational characteristics of the three peptides in micellar media support a membrane-associated mechanism of receptor recognition and activation for the gastrin hormone family and furthermore point to a possible biologically relevant structural motif for gastrin activity.

Receptor-mediated biological responses are prolonged using hydrophobized ligands

Hormone-receptor interactions occur following three-dimensional diffusion of the ligand to the membrane-embedded receptor. However, prior hydrophobization of the ligand might restrict its movement to two dimensions along the membrane surface, and the biological response might therefore be modulated. This idea was tested using the C-terminal nonapeptide, CCK9, of the satiating hormone, cholecystokinin (CCK). The hormone was lipidated by linking it covalently to distearoylphosphatidylethanolamine via a poly(ethylene glycol) (PEG) spacer. The desired conjugate was isolated by thin-layer chromatography and incorporated into preformed small unilamellar dimyristoylphosphatidylcholine (DMPC) vesicles. The hormone-bearing vesicles were injected intraperitoneally into Wistar rats and food intake monitored. Compared to the biological effect elicited by the same amount of soluble non-derivatized CCK9, food intake reduction showed a delayed onset, but lasted for a significantly longer time. We believe this prolonged effect was due to the transfer of the derivatized CCK9 from the vesicles to the natural membrane containing the hormone receptor. Ultimately, this event may result in sustained receptor occupation and, thus, food intake reduction. The underlying mechanism for the physiological effects observed may be of relevance in interpreting results obtained using artificial measuring devices; for example, the signal produced by biosensors may be drastically affected by the hydrophobicity of the ligand.