MOUSE EXTRACELLULAR-SUPEROXIDE DISMUTASE - PRIMARY STRUCTURE, TISSUE-SPECIFIC GENE-EXPRESSION, CHROMOSOMAL LOCALIZATION, AND LUNG IN-SITU HYBRIDIZATION

Extracellular superoxide dismutase (EC-SOD) is the major extracellular antioxidant enzyme. We have determined the primary structure of mouse EC-SOD by characterization of complementary DNA (cDNA) clones and by amino-acid sequence analysis of purified protein. cDNA sequence analys is indicates that mouse EC-SOD is synthesized as a 251-amino-acid prec ursor protein with a predicted molecular weight of 27,400 D. Amino-ter minal micro sequence analysis of purified mature mouse lung EC-SOD dem onstrated the sequence to begin with SSFDLADRLDPV-, These results indi cate that EC-SOD as initially synthesized contains a 24-amino-acid pre cursor peptide, and that the mature protein is 227 amino acids in leng th. Computer algorithms that predict the most Likely site of cotransla tional signal peptidase cleavage suggest that processing will occur be tween amino acids 18 and 19 or 20 and 21, which implies that EC-SOD ma y be initially synthesized as a pre-pro-protein. Like human EC-SOD, ma ture mouse EC-SOD is glycosylated. The full-length mouse EC-SOD cDNA i s 1,834 base pairs long and is 82% (79% for protein) identical to rat EC-SOD, but only 60% (60% for protein) identical to human EC-SOD. The mouse EC-SOD gene locus (Sod3) was mapped by interspecific backcross h aplotype analysis as being 0.9 +/- 0.9 centimorgans distal to the Qdpr locus on mouse Chromosome 5, a position suggesting that the human hom ologue of EC-SOD will map close to the human QDPR locus (4p15.3). Of n ine tissues examined by Northern blot analysis, those of the kidney an d lung are by far the major tissues that express EC-SOD messenger RNA. Using in situ hybridization in the mouse lung, we demonstrate EC-SOD gene expression to be highly localized to alveolar Type II epithelial cells. These data suggest that alveolar Type IT cells play a central r ole in mediating EC-SOD antioxidant function in the lung.