title: C-terminal, endoplasmic reticulum-lumenal domain of prosurfactant protein C - structural features and membrane interactions.
abstract: Surfactant protein C (SP-C) constitutes the transmembrane part of prosurfactant protein C (proSP-C) and is alpha-helical in its native state. The C-terminal part of proSP-C (CTC) is localized in the endoplasmic reticulum lumen and binds to misfolded (beta-strand) SP-C, thereby preventing its aggregation and amyloid fibril formation. In this study, we investigated the structure of recombinant human CTC and the effects of CTC-membrane interaction on protein structure. CTC forms noncovalent trimers and supratrimeric oligomers. It contains two intrachain disulfide bridges, and its secondary structure is significantly affected by urea or heat only after disulfide reduction. The postulated Brichos domain of CTC, with homologs found in proteins associated with amyloid and proliferative disease, is up to 1000-fold more protected from limited proteolysis than the rest of CTC. The protein exposes hydrophobic surfaces, as determined by CTC binding to the environment-sensitive fluorescent probe 1,1'-bis(4-anilino-5,5'-naphthalenesulfonate). Fluorescence energy transfer experiments further reveal close proximity between bound 1,1'-bis(4-anilino-5,5'-naphthalenesulfonate) and tyrosine residues in CTC, some of which are conserved in all Brichos domains. CTC binds to unilamellar phospholipid vesicles with low micromolar dissociation constants, and differential scanning calorimetry and CD analyses indicate that membrane-bound CTC is less structurally ordered than the unbound protein. The exposed hydrophobic surfaces and the structural disordering that result from interactions with phospholipid membranes suggest a mechanism whereby CTC binds to misfolded SP-C in the endoplasmic reticulum membrane.
authors.affiliation: Department of Biochemistry and Molecular Biology I & CIBER Enfermedades Respiratorias, Complutense University of Madrid, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Casals
authors.forename: Hanna
authors.initials: H
authors.lastname: Johansson
authors.forename: Alejandra
authors.initials: A
authors.lastname: Saenz
authors.forename: Magnus
authors.initials: M
authors.lastname: Gustafsson
authors.forename: Carlos
authors.initials: C
authors.lastname: Alfonso
authors.forename: Kerstin
authors.initials: K
authors.lastname: Nordling
authors.forename: Jan
authors.initials: J
authors.lastname: Johansson
mesh_terms: D000595:Amino Acid Sequence; D000817:Anilino Naphthalenesulfonates / Q000737:chemistry; D002151:Calorimetry; D002942:Circular Dichroism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008081:Liposomes / Q000737:chemistry; D008969:Molecular Sequence Data; D010743:Phospholipids / Q000737:chemistry; D017510:Protein Folding; D011498:Protein Precursors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D037721:Pulmonary Surfactant-Associated Protein C / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013696:Temperature; D014461:Ultracentrifugation; D014508:Urea / Q000737:chemistry
chemical_list: D000817:Anilino Naphthalenesulfonates; D008081:Liposomes; D010743:Phospholipids; D011498:Protein Precursors; D037721:Pulmonary Surfactant-Associated Protein C; D011994:Recombinant Proteins; C035763:5,5'-bis(8-(phenylamino)-1-naphthalenesulfonate); D014508:Urea