title: Structural role of counterions adsorbed on self-assembled peptide nanotubes.
abstract: Among noncovalent forces, electrostatic ones are the strongest and possess a rather long-range action. For these reasons, charges and counterions play a prominent role in self-assembly processes in water and therefore in many biological systems. However, the complexity of the biological media often hinders a detailed understanding of all the electrostatic-related events. In this context, we have studied the role of charges and counterions in the self-assembly of lanreotide, a cationic octapeptide. This peptide spontaneously forms monodisperse nanotubes (NTs) above a critical concentration when solubilized in pure water. Free from any screening buffer, we assessed the interactions between the different peptide oligomers and counterions in solutions, above and below the critical assembly concentration. Our results provide explanations for the selection of a dimeric building block instead of a monomeric one. Indeed, the apparent charge of the dimers is lower than that of the monomers because of strong chemisorption. This phenomenon has two consequences: (i) the dimer-dimer interaction is less repulsive than the monomer-monomer one and (ii) the lowered charge of the dimeric building block weakens the electrostatic repulsion from the positively charged NT walls. Moreover, additional counterion condensation (physisorption) occurs on the NT wall. We furthermore show that the counterions interacting with the NTs play a structural role as they tune the NTs diameter. We demonstrate by a simple model that counterions adsorption sites located on the inner face of the NT walls are responsible for this size control.
authors.affiliation: Institut de Biologie et de Technologies de Saclay/Service de Bioénergétique, Biologie Structurale et Mécanismes, Commissariat à l'Énergie Atomique et aux Énergies Alternatives-Saclay, 91191 Gif-sur-Yvette, France. frederic.gobeaux@gmail.com
authors.forename: Frédéric
authors.initials: F
authors.lastname: Gobeaux
authors.forename: Nicolas
authors.initials: N
authors.lastname: Fay
authors.forename: Christophe
authors.initials: C
authors.lastname: Tarabout
authors.forename: Cristelle
authors.initials: C
authors.lastname: Mériadec
authors.forename: Florian
authors.initials: F
authors.lastname: Meneau
authors.forename: Melinda
authors.initials: M
authors.lastname: Ligeti
authors.forename: David-Alexandre
authors.initials: DA
authors.lastname: Buisson
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Cintrat
authors.forename: Khac Minh Huy
authors.initials: KM
authors.lastname: Nguyen
authors.forename: Lionel
authors.initials: L
authors.lastname: Perrin
authors.forename: Céline
authors.initials: C
authors.lastname: Valéry
authors.forename: Franck
authors.initials: F
authors.lastname: Artzner
authors.forename: Maïté
authors.initials: M
authors.lastname: Paternostre
mesh_terms: D000327:Adsorption; D000595:Amino Acid Sequence; D008958:Models, Molecular; D008968:Molecular Conformation; D043942:Nanotubes / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000737:chemistry; D013004:Somatostatin / Q000031:analogs & derivatives / Q000737:chemistry
chemical_list: D010455:Peptides; D010456:Peptides, Cyclic; C060347:lanreotide; D013004:Somatostatin