Structural and functional analysis of the protein products derived from mutant fur alleles in an endoprotease-deficient Chinese hamster ovary cell strain

The fur gene encodes the endoprotease, furin. We recently demonstrated muta tions in both fur alleles in the mutant Chinese hamster ovary (CNO)-K1 stra in, RPE.40, and hypothesized that these mutations were responsible for the endoprotense-deficient phenotype of these cells. We now present the structu ral and functional properties of three protein products derived from the mu tant fur alleles. None of these protein products were able to process the p recursor to von Willebrand factor; which is processed by wild-type furin. P ro-protein processing activity initially, attributed to one of the mutant p roteins was due to wild-type furin produced inadvertently,from one of the e xpression constructs used in these experiments. None of the mutant proteins exhibited evidence of autocatalysis, consistent with the lack of activity versus the test substrate, and glycosylation patterns suggested at least tw o of them remained in the endoplasmic reticulum. These results confirm that RPE.40 cells are furin null mutants, as earlier evidence had suggested.