The Brichos domain of prosurfactant protein C can hold and fold a transmembrane segment.
Prosurfactant protein C (proSP-C) is a 197-residue integral membrane protein, in which the C-terminal domain (CTC, positions 59-197) is localized in the endoplasmic reticulum (ER) lumen and contains a Brichos domain (positions 94-197). Mature SP-C corresponds largely to the transmembrane (TM) region of proSP-C. CTC binds to SP-C, provided that it is in nonhelical conformation, and can prevent formation of intracellular amyloid-like inclusions of proSP-C that harbor mutations linked to interstitial lung disease (ILD). Herein it is shown that expression of proSP-C (1-58), that is, the N-terminal propeptide and the TM region, in HEK293 cells results in virtually no detectable protein, while coexpression of CTC in trans yields SDS-soluble monomeric proSP-C (1-58). Recombinant human (rh) CTC binds to cellulose-bound peptides derived from the nonpolar TM region, but not the polar cytosolic part, of proSP-C, and requires >/=5-residues for maximal binding. Binding of rhCTC to a nonhelical peptide derived from SP-C results in alpha-helix formation provided that it contains a long TM segment. Finally, rhCTC and rhCTC Brichos domain shows very similar substrate specificities, but rhCTC(L188Q), a mutation linked to ILD is unable to bind all peptides analyzed. These data indicate that the Brichos domain of proSP-C is a chaperone that induces alpha-helix formation of an aggregation-prone TM region.
Johansson
Hanna
H
Department of Anatomy, Physiology and Biochemistry, SLU, The Biomedical Centre, Uppsala, Sweden.
Eriksson
Maria
M
Nordling
Kerstin
K
Presto
Jenny
J
Johansson
Jan
J
D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry; D002942:Circular Dichroism; D006801:Humans; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D037721:Pulmonary Surfactant-Associated Protein C / Q000737:chemistry* / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics
D037721:Pulmonary Surfactant-Associated Protein C; D011994:Recombinant Proteins; C489679:SFTPC protein, human