surfactant protein B
The SFTPB gene provides instructions for making a protein called surfactant protein-B (SP-B). This protein is one of four proteins (each produced from a different gene) in surfactant, a mixture of certain fats (called phospholipids) and proteins that lines the lung tissue and makes breathing easy. Without normal surfactant, the tissue surrounding the air sacs in the lungs (the alveoli) sticks together after exhalation (because of a force called surface tension), causing the alveoli to collapse. As a result, filling the lungs with air on each breath becomes very difficult, and the delivery of oxygen to the body is impaired. Surfactant lowers surface tension, easing breathing and avoiding lung collapse. The SP-B protein helps spread the surfactant across the surface of the lung tissue, aiding in the surface tension-lowering property of surfactant.
The phospholipids and proteins that make up surfactant are packaged in cellular structures known as lamellar bodies, which are found in specialized lung cells. The surfactant proteins must go through several processing steps to mature and become functional; some of these steps occur in lamellar bodies. The SP-B protein plays a role in the formation of lamellar bodies and, thus, affects the processing of a surfactant protein called surfactant protein-C (SP-C).
More than 30 mutations in the SFTPB gene that cause surfactant dysfunction have been identified. Surfactant dysfunction due to SFTPB gene mutations (often called SP-B deficiency) causes severe, often fatal breathing problems in newborns. These mutations lead to partial or complete loss of mature SP-B, resulting in abnormal composition of surfactant and decreased surfactant function. In addition, lamellar body formation is impaired. The lack of normal lamellar bodies leads to abnormal processing of SP-C, resulting in a reduction of mature SP-C and a buildup of unprocessed forms of SP-C. The loss of functional surfactant raises surface tension in the alveoli, causing difficulty breathing and collapse of the lungs. The combination of SP-B and SP-C dysfunction may explain why the signs and symptoms of SP-B deficiency are so severe.
- 6 kDa protein
- 18 kDa pulmonary-surfactant protein
- pulmonary surfactant-associated protein B
- pulmonary surfactant-associated proteolipid SPL(Phe)