Surfactant protein C (SP-C), is one of the
pulmonary surfactant proteins. In humans this is encoded by the ''SFTPC''
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
.
It is a
membrane protein
Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Integral membrane proteins are a permanent part of a cell membrane ...
.
Structure
SFTPC is a 197-residue protein made up of two halves: a unique N-terminal
propeptide
A protein precursor, also called a pro-protein or pro-peptide, is an inactive protein (or peptide) that can be turned into an active form by post-translational modification, such as breaking off a piece of the molecule or adding on another molecule ...
domain and a C-terminal
BRICHOS domain. The around 100-aa long propeptide domain actually contains not only the cleaved part, but also the mature peptide. 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.
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
Amyloids are aggregates of proteins characterised by a Fibril, fibrillar morphology of 7–13 Nanometer, nm in diameter, a beta sheet (β-sheet) Secondary structure of proteins, secondary structure (known as cross-β) and ability to be Staining, ...
fibrils. The correct intracellular trafficking of proSP-C has also been reported to depend on the propeptide.
The structure of the BRICHOS domain has been solved. Mutations in this domain also lead to amyloid fibrils made up of the mature peptide, suggesting a
chaperone activity.
Clinical significance
Mutations are associated with
surfactant metabolism dysfunction
Surfactant metabolism dysfunction is a condition where pulmonary surfactant is insufficient for adequate respiration. Surface tension at the liquid-air Interface (matter), interphase in the Pulmonary alveolus, alveoli makes the air sacs prone to c ...
type 2.
Humans and animals born lacking SP-C tend to develop progressive
interstitial lung disease
Interstitial lung disease (ILD), or diffuse parenchymal lung disease (DPLD), is a group of respiratory diseases affecting the interstitium (the tissue and space around the alveoli (air sacs)) of the lungs. It concerns alveolar epithelium, pulmo ...
.
Recombinant SP-C is used in Venticute, an artificial lung surfactant.
A process to mass-produce an analogue called rSP-C33Le by fusion with
spidroin
Spidroins are the main proteins in spider silk. Different types of spider silk contain different spidroins, all of which are members of a single protein family. The most-researched type of spidroins are the major ampullate silk proteins (MaSp ...
has been described.
References
Further reading
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External links
GeneReviews/NIH/NCBI/UW entry on Pulmonary Fibrosis, Familial*
Protein domains
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