It can be further broken down into a 23-aa helical transmembrane propeptide proper, the mature secreted SP-C (24-58), and a linker (59-89) that connects to the BRICHOS domain.

[8] The propeptide of pulmonary surfactant C has an N-terminal alpha-helical segment whose suggested function was stabilization of the protein structure, since the mature peptide can irreversibly transform from its native alpha-helical structure to beta-sheet aggregates and form amyloid fibrils.

The correct intracellular trafficking of proSP-C has also been reported to depend on the propeptide.

Mutations in this domain also lead to amyloid fibrils made up of the mature peptide, suggesting a chaperone activity.

Humans and animals born lacking SP-C tend to develop progressive interstitial lung disease.