On the self-assembly properties of the Growth Hormone Releasing Hexapeptide

BARBOSA, LRS; SANTANA, H; AVILA CL; CABRERA, I; PÁEZ, R; FALCÓN, V; PESSOA, JR. A; VENTOSA, N; VECIANA, J; ITRI R

Caxambu

Congreso; XXIX Reunion Anual FESBE; 2014

Federacion de Sociedades de Biologia Experimental

Growth hormone releasing peptide, GHRP-6, is a synthetic hexapeptide (His-(D-Trp)-Ala-Trp-(D-Phe)-Lys-NH2,). It belongs to a class of synthetic growth hormone secretagogues, which stimulate growth hormone secretion from somatotrophs in several species including humans. Even though its use for the treatment of several human diseases is being explored, there is also an increased interest in its self-assembly properties and its application in the field of nanotechnology. In this study, we shed light into the self-assembling properties of GHRP-6, by using small angle X-ray scattering, transmission electronic microscopy (TEM), and molecular dynamics simulation. The combined results demonstrated that GHRP-6 at 20 mg/mL in phosphate buffer self-assembles into very long nanotubes, with inner and outer cross-sections of 7(1) and 13(1) nm. At concentrations > 30 mg/ml, these nanotubes form bundles with hexagonal arrangement, with center-to-center distance of circa 15 nm. Within the nanotube, the peptides self-assemble in a partially interdigitated structure with the amino termini at the peptide water interface. While the carboxi termini remains buried, the long side chain of Lys-6 stretch out of the hydrophobic core to the cylinder surface. Interestingly, such arrangement is quite similar to that observed on cationic lipidic vesicles. Nevertheless, the cross-section dimension of GHRP-6 nano-assemble is rather small as compared to others surfactant-like peptides, a fact that could be exploited in the design of new nanomaterials.