Structure, Function, and Regulation of Pulmonary Surfactant Proteins

Proteins comprise approximately 10% of the mass of pulmonary surfactant, the remainder consisting primarily of phospholipids which are enriched in phosphatidylcholine and phosphatidylglycerol. Phospholipid components of pulmonary surfactant are found in the alveolus of the lung in a variety of aggregate forms, including multilamellar, tubular myelin, and vesicular structures, each representing various stages in the life cycle of surfactant. The ability of surfactant to adsorb rapidly to a surface and to generate low surface tension during dynamic compression is distinct from the properties of phospholipids themselves. The structure, function, and metabolism of pulmonary surfactant are now thought to be strongly influenced by the presence of surfactant proteins. Considerable progress has been made in the isolation and characterization of lung-specific proteins which are intimately associated with surfactant phospholipids. The role of these proteins in surfactant homeostasis has been the subject of several recent reviews. ¹³ The present work will describe aspects of the regulation, structure, and function of four surfactant proteins, surfactant proteins A, B, C, and D.