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. Oligomeric complex of 6 set of homotrimers. N-acetylated. At least 6 alleles of SFTPA2 are known: 1A, 1A(0), 1A(1), 1A(2), 1A(3) and 1A(4). The sequence shown is that of allele 1A(2). The disease is caused by variants affecting the gene represented in this entry. Pulmonary surfactant consists of 90% lipid and 10% protein. 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). Belongs to the SFTPA family.