title: Folding and Intramembraneous BRICHOS Binding of the Prosurfactant Protein C Transmembrane Segment.
abstract: Surfactant protein C (SP-C) is a novel amyloid protein found in the lung tissue of patients suffering from interstitial lung disease (ILD) due to mutations in the gene of the precursor protein pro-SP-C. SP-C is a small α-helical hydrophobic protein with an unusually high content of valine residues. SP-C is prone to convert into β-sheet aggregates, forming amyloid fibrils. Nature's way of solving this folding problem is to include a BRICHOS domain in pro-SP-C, which functions as a chaperone for SP-C during biosynthesis. Mutations in the pro-SP-C BRICHOS domain or linker region lead to amyloid formation of the SP-C protein and ILD. In this study, we used an in vitro transcription/translation system to study translocon-mediated folding of the WT pro-SP-C poly-Val and a designed poly-Leu transmembrane (TM) segment in the endoplasmic reticulum (ER) membrane. Furthermore, to understand how the pro-SP-C BRICHOS domain present in the ER lumen can interact with the TM segment of pro-SP-C, we studied the membrane insertion properties of the recombinant form of the pro-SP-C BRICHOS domain and two ILD-associated mutants. The results show that the co-translational folding of the WT pro-SP-C TM segment is inefficient, that the BRICHOS domain inserts into superficial parts of fluid membranes, and that BRICHOS membrane insertion is promoted by poly-Val peptides present in the membrane. In contrast, one BRICHOS and one non-BRICHOS ILD-associated mutant could not insert into membranes. These findings support a chaperone function of the BRICHOS domain, possibly together with the linker region, during pro-SP-C biosynthesis in the ER.
authors.affiliation: From the Department of Biochemistry and Molecular Biology I, Complutense University of Madrid, 28040 Madrid, Spain, the Centro de Investigación Biomédica en Red de Enfermedades Respiratorias (CIBERES), Instituto de Salud Carlos III, 28029 Madrid, Spain.
authors.forename: Alejandra
authors.initials: A
authors.lastname: Sáenz
authors.affiliation: the Center for Alzheimer Research, NVS (Neurobiology, Care Sciences, and Society) Department, Karolinska Institutet, S-141 57 Huddinge, Sweden, and.
authors.forename: Jenny
authors.initials: J
authors.lastname: Presto
authors.affiliation: the Department of Biochemistry and Biophysics, Center for Biomembrane Research, Stockholm University, S-10691 Stockholm, Sweden.
authors.forename: Patricia
authors.initials: P
authors.lastname: Lara
authors.affiliation: the Department of Biochemistry and Biophysics, Center for Biomembrane Research, Stockholm University, S-10691 Stockholm, Sweden.
authors.forename: Laura
authors.initials: L
authors.lastname: Akinyi-Oloo
authors.affiliation: the Centro de Investigación Biomédica en Red de Enfermedades Respiratorias (CIBERES), Instituto de Salud Carlos III, 28029 Madrid, Spain.
authors.forename: Belén
authors.initials: B
authors.lastname: García-Fojeda
authors.affiliation: the Department of Biochemistry and Biophysics, Center for Biomembrane Research, Stockholm University, S-10691 Stockholm, Sweden.
authors.forename: IngMarie
authors.initials: I
authors.lastname: Nilsson
authors.affiliation: the Center for Alzheimer Research, NVS (Neurobiology, Care Sciences, and Society) Department, Karolinska Institutet, S-141 57 Huddinge, Sweden, and janne.johansson@ki.se.
authors.forename: Jan
authors.initials: J
authors.lastname: Johansson
authors.affiliation: From the Department of Biochemistry and Molecular Biology I, Complutense University of Madrid, 28040 Madrid, Spain, the Centro de Investigación Biomédica en Red de Enfermedades Respiratorias (CIBERES), Instituto de Salud Carlos III, 28029 Madrid, Spain, ccasalsc@ucm.es.
authors.forename: Cristina
authors.initials: C
authors.lastname: Casals
mesh_terms: D058227:Amyloidogenic Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000818:Animals; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D017563:Lung Diseases, Interstitial / Q000235:genetics / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D017510:Protein Folding; D054730:Protein Interaction Domains and Motifs; D011498:Protein Precursors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D037721:Pulmonary Surfactant-Associated Protein C / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D058227:Amyloidogenic Proteins; D008563:Membrane Lipids; D011498:Protein Precursors; D037721:Pulmonary Surfactant-Associated Protein C; D011994:Recombinant Proteins
keywords: amyloid diseases; amyloid-like fibril; chaperone activity; lipid bilayer; lipid-binding protein; lipid-protein interactions; lung; membrane structure; protein folding; pulmonary surfactant