Structural and functional similarities between the major hemolymph protein of fall armyworm and cat C4 binding...

We have investigated the structural and functional similarities between insect (armyworm) major larval serum protein (LSP-I) and mammalian (Cat) C4 binding protein (i) by comparing the major chymotryptic peptide patterns using sodium dodecyl sulfate polyacrylamide gel electrophoresis and (ii) their ability to prevent assembly of classical C3 convertase (EAC142). Both Cat C4 bp and Spodoptera LSP-I are composed of identical subunits of Mr = 75,000 and Mr = 80,000, respectively and generate the characteristic cleavage product of Mr = 50,000 on limited proteolysis. These observations are interpreted as an indication that the major hemolymph protein (LSP-I) of fall armyworm is a homologue of the C4bp of the mammalian complement system.