Surfactant protein C

Surfactant protein C (SP-C), is one of the pulmonary surfactant proteins. In humans this is encoded by the SFTPC gene.^[5][6][7]

SFTPC
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 2YAD
Identifiers
Aliases	SFTPC, BRICD6, PSP-C, SFTP2, SMDP2, SP-C, surfactant protein C, SP5
External IDs	OMIM: 178620; MGI: 109517; HomoloGene: 2271; GeneCards: SFTPC; OMA:SFTPC - orthologs
Gene location (Human) Chr. Chromosome 8 (human)[1] Band 8p21.3 Start 22,156,913 bp[1] End 22,164,479 bp[1]
Gene location (Mouse) Chr. Chromosome 14 (mouse)[2] Band 14 D2|14 36.32 cM Start 70,758,389 bp[2] End 70,761,521 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in lower lobe of lung right lung upper lobe of lung upper lobe of left lung visceral pleura tendon of biceps brachii C1 segment parotid gland apex of heart internal globus pallidus Top expressed in right lung lobe left lung lobe morula pulmonary alveolus human fetus alveolar duct sexually immature organism lip pulmonary alveolar epithelium lung parenchyma More reference expression data BioGPS More reference expression data
Gene ontology Molecular function protein binding identical protein binding Cellular component extracellular region clathrin-coated endocytic vesicle lamellar granule endoplasmic reticulum membrane multivesicular body lumen extracellular space Biological process respiratory gaseous exchange by respiratory system Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 6440 20389 Ensembl ENSG00000168484 ENSMUSG00000022097 UniProt P11686 P21841 Q6P8P8 RefSeq (mRNA) NM_001172357 NM_001172410 NM_003018 NM_001317778 NM_001317779 NM_001317780 NM_011359 RefSeq (protein) NP_001165828 NP_001165881 NP_001304707 NP_001304708 NP_001304709 NP_003009 NP_035489 Location (UCSC) Chr 8: 22.16 – 22.16 Mb Chr 14: 70.76 – 70.76 Mb PubMed search [3] [4]
Wikidata
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It is a membrane protein.

Structure

Surfactant protein C, N terminal propeptide
Pig SP-C, corresponds to human mature form
Identifiers
Symbol	SP_C-Propep
Pfam	PF08999
InterPro	IPR001729
PROSITE	PDOC00298
OPM superfamily	69
OPM protein	1spf
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

SFTPC is a 197-residue protein made up of two halves: a unique N-terminal propeptide 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.^[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.^[9]

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.^[8]

Clinical significance

Mutations are associated with surfactant metabolism dysfunction type 2.

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

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 has been described.^[10]