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Production of recombinant Der fI with the native IgE-binding activity using a baculovirus expression system.

Der fI is a cysteine protease contained in feces of mites and is one of major mite allergens. Recombinant Der fI (reDer fI) that is produced using a baculovirus expression system contains pro-sequences of different lengths. Most of these can be removed by acid treatment. However, IgE-binding activity of acid-treated reDer fI is lower than that of native Der fI at high protein concentrations, and N-terminal amino acids of acid-treated reDer fI are not uniform. Now, a method for processing of the pro-sequence has been developed by producing reDer fI E(-1)K with baculovirus expression system in which the carboxy terminal amino acid of the pro-sequence (glutamate) was replaced by lysine using site directed mutagenesis. No difference in the amount of production was observed upon introducing the mutation into the pro-sequence. Addition of lysylendopeptidase into the culture medium led to processing of the pro-sequence of reDer fI E(-1)K and proceeded the degradation of the other proteins in the medium. Lysylendopeptidase-treated reDer fI E(-1)K was easily purified with an anion exchange column, resulting in 20% increase of the yield. Lysylendopeptidase-treated reDer fI E(-1)K obtained through these processes was compared with the native Der fI. Although some differences were found in protease activity and reactivity with lectins, their N-terminal amino acid and the IgE-binding activity were the same as those of the native one, indicating its usefulness for diagnostic purpose.