Assignment of SOD3 to human chromosome band 4p15.3→p15.1 with somatic cell and radiation hybrid mapping, linkage mapping, and fluorescent in-situ hybridization

Abstract

The superoxide dismutases (E.C. 1.15.1.1) are ubiquitous, essential enzymes that protect cellular macromolecules from damage by reactive oxygen species (Fridovich, 1995). EC-SOD, the product of the SOD3 gene, is the major antioxidant enzyme found in the extracellular milieu (Marklund et al., 1982, 1986; Karlsson and Marklund, 1988). EC-SOD is a homotetramer of 130 kDa. Each EC-SOD subunit consists of 222 amino acids, and has single bound copper and zinc ions (Hjalmarsson et al., 1987). Mature EC-SOD contains carbohydrate and has an Nlinked glycosylation site at asparagine 89 (Hjalmarsson et al., 1987). A prominent feature of EC-SOD is its high affinity for glycosaminoglycans (Karlsson and Marklund, 1987), as a result of a lysine and arginine-rich, 20-amino-acid heparin-binding domain at the C-terminus of the protein (Hjalmarsson et al., 1987; Sandstrom et al., 1992). This affinity for heparin causes EC-SOD to be a ‘tissue interstitial enzyme’ (Sandstrom et al., 1993), bound to heparin sulfate proteoglycans associated with the glycocalyx of endothelial cell surfaces and the extracellular matrix (Karlsson and Marklund, 1987). Although EC-SOD can be measured in plasma, lymph, cerebrospinal, and synovial fluids (Marklund et al., 1982, 1986; Karlsson and Marklund, 1988), most EC-SOD present in bodily fluids represents enzyme with proteolytically altered heparin-binding sites (Sandstrom et al., 1993). Almost all human tissues contain measurable levels of EC-SOD (Marklund, 1984) and at least eight different tissues, including heart, lung, and placenta, synthesize EC-SOD mRNA (Folz and Crapo, 1994). An understanding of why a superoxide dismutase is required in the extracellular spaces remains elusive. The SOD3 gene was previously localized to 4pter→4q21 (Hendrickson et al., 1990). We have undertaken a more precise mapping of the SOD3 gene to determine if it may represent a locus corresponding to any known hereditary human disorders. We report localization of SOD3 to 4p15.3→15.1 by the techniques of somatic cell hybrid mapping, fluorescent in situ hybridization (FISH), linkage mapping, and radiation hybrid mapping.