Glycyl-phenylalanine

Neuropeptides that act as muscle relaxants have been identified in chordates and protostomian invertebrates but little is known about the molecular identity of neuropeptides that act as muscle relaxants in deuterostomian invertebrates (e.g. echinoderms) that are 'evolutionary intermediates' of chordates and protostomes. Here, we have used the apical muscle of the starfish Patiria pectinifera to assay for myorelaxants in extracts of this species. A hexadecapeptide with the amino acid sequence Phe-Gly-Lys-Gly-Gly-Ala-Tyr-Asp-Pro-Leu-Ser-Ala-Gly-Phe-Thr-Asp was identified and designated starfish myorelaxant peptide (SMP). Cloning and sequencing of a cDNA encoding the SMP precursor protein revealed that it comprises 12 copies of SMP as well as 3 peptides (7 copies in total) that are structurally related to SMP. Analysis of the expression of SMP precursor transcripts in P. pectinifera using qPCR revealed the highest expression in the radial nerve cords and lower expression levels in a range of neuromuscular tissues, including the apical muscle, tube feet and cardiac stomach.

During the last decades opioid peptides, like enkephalins (Tyr-Gly-Gly-Phe-Met/Leu) are subject to extensive studies due to their antinociceptive action in organism. According to the membrane catalysis theory, in order to adopt a proper conformation for binding to their receptors, opioid peptides interact with the lipid phase of the membrane receptor surrounding. With this regard, the aim of the present work was to study the effects of synthetic leucine-enkephalin and leucine-enkephalinamide on surface characteristics and morphology of lipid monolayers, composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, sphingomyelin, and cholesterol alone and with their mixtures. The lipids were chosen to represent a model of a membrane raft, since it is known that G-protein-coupled receptors, including opioid receptors, are located preferably in membrane rafts. By using Langmuir's monolayer method, the change in surface pressure of the model membranes before and after the addition of the synthetic enkephalins was studied, and the compressional moduli of the lipids and lipid-peptides monolayers were determined.

A bacterial collagen-like protein Scl2 has been developed as a recombinant collagen model system to host human collagen ligand-binding sequences, with the goal of generating biomaterials with selective collagen bioactivities. Defined binding sites in human collagen for integrins, fibronectin, heparin, and MMP-1 have been introduced into the triple-helical domain of the bacterial collagen and led to the expected biological activities. The modular insertion of activities is extended here to the discoidin domain receptors (DDRs), which are collagen-activated receptor tyrosine kinases. Insertion of the DDR-binding sequence from human collagen III into bacterial collagen led to specific receptor binding. However, even at the highest testable concentrations, the construct was unable to stimulate DDR autophosphorylation. The recombinant collagen expressed in Escherichia coli does not contain hydroxyproline (Hyp), and complementary synthetic peptide studies showed that replacement of Hyp by Pro at the critical Gly-Val-Met-Gly-Phe-Hyp position decreased the DDR-binding affinity and consequently required a higher concentration for the induction of receptor activation.

The kinetics of interaction of dipeptide glycylphenylalanine (Gly-Phe) with ninhydrin have been studied by following the reaction spectrophotometrically at 70 °C and a particular pH 5.0 in the absence and presence of conventional cetyltrimethylammonium bromide (CTAB) and gemini (alkanediyl-α,ω-bis(dimethylhexadecylammonium bromide)) surfactants. The rate shows first- and fractional-order dependence on [Gly-Phe] and [ninhydrin], respectively. The surfactants were found to catalyse the reaction. Furthermore, whereas the typical rate constant (kΨ) increase and leveling-off regions are observed with geminis, just like as seen with conventional surfactants, the former produced a third region of increasing kΨ at higher concentrations. A kinetic rate law consistent with experimental results has been derived on the basis of the proposed mechanism.