EXTRACELLULAR AND CYTOPLASMIC CUZN SUPEROXIDE DISMUTASES FROM BRUGIA LYMPHATIC FILARIAL NEMATODE PARASITES

We have isolated full-length cDNAs encoding two distinct types of CuZn superoxide dismutases (SODs) from the filarial nematode parasite Brug ia pahangi. The derived amino acid sequences suggested that one class of cDNAs represented a cytoplasmic form of SOD and the second class re presented an extracellular (EC) variant. The predicted proteins were h ighly homologous to each other, but the sequence of the latter contain ed an additional 43 residues at the N terminus, the first 16 of which were markedly hydrophobic, and four potential sites for N-linked glyco sylation. Western blotting (immunoblotting) with an antiserum to a par tial SOD expressed in Escherichia coli revealed two proteins with esti mated molecular masses of 19 and 29 kDa. Digestion with N-glycanase in dicated that the latter protein corresponded to the EC form, as it pos sessed N-linked oligosaccharide chains at three sites, leaving a pepti de backbone with an estimated molecular mass of 22 kDa, which was cons istent with the additional 27 amino acids predicted from the cDNA sequ ence. Gel filtration indicated that both enzymes were dimeric in their native forms, in contrast to the human EC-SOD, which is tetrameric. C omparison of the primary structure of the parasite EC-SOD with that of the human EC enzyme revealed two major differences: the N-terminal ex tension of the parasite enzyme was shorter by 25 residues, and it also lacked the C-terminal charged extension which mediates binding to cel l surface sulfated proteoglycans. Lavage of Mongolian jirds infected i ntraperitoneally with Brugia malayi resulted in the recovery of filari al CuZn SODs, principally the EC form, indicating that this form of SO D is secreted in vivo. This EC enzyme may contribute to parasite persi stence by neutralizing superoxide generated by activated leukocytes, t hus acting as both an antioxidant and an anti-inflammatory factor.