Pulmonary surfactant is a surface-active lipoprotein complex (phospholipoprotein) formed by type II alveolar cells. The proteins and lipids that surfactant comprises have both a hydrophilic region and a hydrophobic region. By adsorbing to the air-water interface of alveoli with the hydrophilic head groups in the water and the hydrophobic tails facing towards the air, the main lipid component of surfactant, dipalmitoylphosphatidylcholine (DPPC), reduces surface tension.
Pulmonary surfactant consists of 90% lipid and 10% protein.
Pulmonary Surfactant Pathophysiology: Current Models and Open Questions, 2010
Synthesis of the protein and phospholipid components of surfactant may proceed via separate pathways (green lines). SP-B and SP-C traffic through the Golgi and late endosome/multivesicular body (MVB) to the lamellar body. In contrast, surfactant phospholipids may traffic directly from the ER to the lamellar body; phospholipid transfer protein(s) (PLTP) and ABC transporters likely play an important role in phospholipid trafficking. (It is also possible that direct contact between the ER and lamellar body may facilitate phospholipid transfer; see text.) Transcriptional pathways involved in coordinated regulation of surfactant protein and phospholipid synthesis are indicated by black arrows. Surfactant components internalized from the airspaces may also contribute to biosynthesis (red lines).
Pulmonary surfactant is a lipid:protein complex containing dipalmitoyl-phosphatidylcholine (DPPC) as the major component. Recent studies indicate adsorbed surfactant films consist of a surface monolayer and a monolayerassociated
Lipid compositional analysis of pulmonary surfactant monolayers and monolayer-associated reservoirs, 2003
Effect of dexamethasone on the synthesis of dipalmitoyl phosphatidylcholine. 1981
Glucocorticoids are known to enhance surfactant production by stimulating the formation of phosphatidylcholine.
There are 4 surfactant-associated proteins: 2 collagenous, carbohydrate-binding glycoproteins (SP-A and SP-D) and 2 small hydrophobic proteins (SP-B and SP-C).
- Pulmonary surfactant-associated protein B (SFTCB)
- Pulmonary surfactant-associated proteins promote alveolar stability by lowering the surface tension at the air-liquid interface in the peripheral air spaces. SP-B increases the collapse pressure of palmitic acid to nearly 70 millinewtons per meter.
- Pulmonary surfactant-associated protein C (SFTPC)
- Pulmonary surfactant associated proteins promote alveolar stability by lowering the surface tension at the air-liquid interface in the peripheral air spaces.
- Pulmonary surfactant-associated protein D (SP
- Contributes to the lung's defense against inhaled microorganisms. May participate in the extracellular reorganization or turnover of pulmonary surfactant. Binds strongly maltose residues and to a lesser extent other alpha-glucosyl moieties.
- Pulmonary surfactant-associated protein A2 (SFTPA2)
- In presence of calcium ions, it binds to surfactant phospholipids and contributes to lower the surface tension at the air-liquid interface in the alveoli of the mammalian lung and is essential for normal respiration.
CHEMICAL STRUCTURE AND IMAGES
When relevant for the function
- Primary structure
- Secondary structure
- Tertiary structure
- Quaternary structure
Protein Aminoacids Percentage
The Protein Aminoacids Percentage gives useful information on the local environment and the metabolic status of the cell (starvation, lack of essential AA, hypoxia)
Protein Aminoacids Percentage
SYNTHESIS AND TURNOVER
Surfactant components are synthesized, secreted and recycled by type II epithelial cells in the alveolus. With the exception of SP-A, surfactant proteins are synthesized in polyribosomes, modified in the endoplasmic reticulum, Golgi apparatus and multivesicular bodies and stored in lamellar bodies before secretion. Surfactant phospholipids are synthesized in the endoplasmic reticulum, transported through the Golgi apparatus into multivesicular bodies and packaged into lamellar bodies. After exocytosis of lamellar bodies, surfactant phospholipids, in the presence of SP-A, SP-B and Ca2+, are organized into a lattice structure called tubular myelin ™, which forms a lipid-rich layer at the air-liquid interface of the alveolus. Most of the extracellular surfactant is taken up by type II cells, catabolized and transported into lamellar bodies for recycling. Alveolar macrophages also take part in the catabolization process of the surfactant components (Gurel et al 2001).
Pulmonary surfactant: a front line of lung host defense, 2003
- Cell signaling and Ligand transport
- Structural proteins
Genetic Defects in Surfactant Protein A2 Are Associated with Pulmonary Fibrosis and Lung Cancer 2009