'Shed' furin: mapping of the cleavage determinants and identification of its C-terminus

The human endoprotease furin is involved in the proteolytic maturation of t he precursor molecules of a wide variety of bioactive proteins. Despite its localization in the membranes of the trans-Golgi system by means of a tran smembrane domain, it has repeatedly been reported to form a C-terminally tr uncated, naturally secreted form referred to as 'shed' furin. In order to i dentify the cleavage site, internal deletion mutants of increasing size, N- terminal to Leu(708), and subsequently individual amino acid substitutions were introduced, and Arg(683) was identified as the prime determinant for s hedding. MS analysis determined Ser(682) as the C-terminus of shed furin, s uggesting that monobasic cleavage may occur N-terminal to Arg(683). Alterat ion of Arg(683) directs the shedding mechanism to alternative cleaving site s previously unused.