1 research outputs found
Structural Role of Counterions Adsorbed on Self-Assembled Peptide Nanotubes
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 dimerādimer interaction is less
repulsive than the monomerāmonomer 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