title: Evidence of PPII-like helical conformation and glass transition in a self-assembled solid-state polypeptide-surfactant complex: poly(L-histidine)/docylbenzenesulfonic acid.
abstract: We present lamellar self-assembly of cationic poly(L-histidine) (PLH) stoichiometrically complexed with an anionic surfactant, dodecyl benzenesulfonic acid (DBSA), which allows a stabilized conformation reminiscent of polyproline type II (PPII) left-handed helices. Such a conformation has no intrapeptide hydrogen bonds, and it has previously been found to be one source of flexibility, e.g., in collagen and elastin, as well as an intermediate in silk processing. PLH(DBSA)1.0 complexes were characterized by Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The PPII-like conformation in PLH(DBSA)1.0 is revealed by characteristic CD and FTIR spectra, where the latter indicates absence of intrachain peptide hydrogen bonds. In addition, a glass transition was directly verified by DSC at ca. 135 degrees C for PLH(DBSA)1.0 and indirectly by SAXS and TEM in comparison to pure PLH at 165 degrees C, thus indicating plasticization. Glass transitions have not been observed before in polypeptide-surfactant complexes. The present results show that surfactant binding can be a simple scheme to provide steric crowding to stabilize PPII conformation to tune the polypeptide properties, plasticization and flexibility.
authors.affiliation: Centre of Excellence of Academy of Finland.
authors.forename: Ramasubbu
authors.initials: R
authors.lastname: Ramani
authors.forename: Sirkku
authors.initials: S
authors.lastname: Hanski
authors.forename: Ari
authors.initials: A
authors.lastname: Laiho
authors.forename: Roman
authors.initials: R
authors.lastname: Tuma
authors.forename: Simo
authors.initials: S
authors.lastname: Kilpeläinen
authors.forename: Filip
authors.initials: F
authors.lastname: Tuomisto
authors.forename: Janne
authors.initials: J
authors.lastname: Ruokolainen
authors.forename: Olli
authors.initials: O
authors.lastname: Ikkala
mesh_terms: D001557:Benzenesulfonates / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D044367:Phase Transition; D017433:Protein Structure, Secondary; D013501:Surface-Active Agents
chemical_list: D001557:Benzenesulfonates; D010455:Peptides; D013501:Surface-Active Agents; C011083:polyproline; C033223:polyhistidine; D006639:Histidine; C032365:benzenesulfonic acid