Surfactant protein C (SP-C) constitutes the transmembrane part of prosurf-actant protein C (proSP-C) and isa-helical in its native state. The C-termi-nal part of proSP-C (CTC) is localized in the endoplasmic reticulum lumen and binds to misfolded (b-strand) SP-C, thereby preventing its aggregation and amyloid fibril formation.