title: Low concentration structural dynamics of lanreotide and somatostatin-14.
abstract: Lanreotide, a synthetic cyclic octapeptide, analogue of the peptide hormone somatostatin-14 (SST-14), is routinely used as a long-acting medication in the management of neuroendocrine tumors. Despite its therapeutic importance, low concentration structural data is still lacking for lanreotide. In fact, the major part of the previous structural investigations were focused on the remarkable aggregation properties of this peptide, appearing at high concentrations (>5 mM). Here, we have applied three optical spectroscopic techniques, i.e. fluorescence, circular dichroism and Raman scattering, for analyzing the structural dynamics at the concentrations below 5 mM, where lanreotide exists either in a monomer state or at the first stages of aggregation. The obtained data from lanreotide were discussed through their comparison with those collected from SST-14, leading us to the following conclusions: (i) The central D-Trp residue, forming with its adjacent Lys the main receptor interacting part of lanreotide, keeps a constant high rotational freedom whatever the environment (water, water/methanol, methanol). (ii) A solvent-dependent tight β-turn, belonging to the type-II' family, is revealed in lanreotide. (iii) Raman data analyzed by band decomposition in the amide (I and III) regions allowed estimation of different secondary structural elements within the millimolar range. Interestingly, the applied protocol shows a perfect agreement between the structural features provided by the amide I and amide III Raman markers.
authors.affiliation: Groupe de Biophysique Moléculaire, UFR Santé-Médecine-Biologie Humaine, Université Paris 13, Sorbonne Paris Cité, 74 rue Marcel Cachin, 93017 Bobigny, cedex, France.
authors.forename: Belén
authors.initials: B
authors.lastname: Hernández
authors.forename: Yves-Marie
authors.initials: YM
authors.lastname: Coïc
authors.forename: Bruno
authors.initials: B
authors.lastname: Baron
authors.forename: Sergei G
authors.initials: SG
authors.lastname: Kruglik
authors.forename: Fernando
authors.initials: F
authors.lastname: Pflüger
authors.forename: Régis
authors.initials: R
authors.lastname: Cohen
authors.forename: Claude
authors.initials: C
authors.lastname: Carelli
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Ghomi
mesh_terms: D016880:Anisotropy; D002942:Circular Dichroism; D010456:Peptides, Cyclic / Q000737:chemistry*; D017433:Protein Structure, Secondary; D012399:Rotation; D012997:Solvents; D013004:Somatostatin / Q000031:analogs & derivatives* / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013059:Spectrum Analysis, Raman; D014364:Tryptophan / Q000737:chemistry
chemical_list: D010456:Peptides, Cyclic; D012997:Solvents; C060347:lanreotide; D013004:Somatostatin; D014364:Tryptophan
keywords: Raman scattering; circular dichroism; fluorescence; lanreotide; somatostatin-14; structural dynamics; type-II' β-turn