Mammalian subtilisin/kexin isozyme SKI-1: A widely expressed proprotein convertase with a unique cleavage specificity and cellular localization

Proc Natl Acad Sci U S A. 1999 Feb 16;96(4):1321-6. doi: 10.1073/pnas.96.4.1321.


Using reverse transcriptase-PCR and degenerate oligonucleotides derived from the active-site residues of subtilisin/kexin-like serine proteinases, we have identified a highly conserved and phylogenetically ancestral human, rat, and mouse type I membrane-bound proteinase called subtilisin/kexin-isozyme-1 (SKI-1). Computer databank searches reveal that human SKI-1 was cloned previously but with no identified function. In situ hybridization demonstrates that SKI-1 mRNA is present in most tissues and cells. Cleavage specificity studies show that SKI-1 generates a 28-kDa product from the 32-kDa brain-derived neurotrophic factor precursor, cleaving at an RGLT downward arrowSL bond. In the endoplasmic reticulum of either LoVo or HK293 cells, proSKI-1 is processed into two membrane-bound forms of SKI-1 (120 and 106 kDa) differing by the nature of their N-glycosylation. Late along the secretory pathway some of the membrane-bound enzyme is shed into the medium as a 98-kDa form. Immunocytochemical analysis of stably transfected HK293 cells shows that SKI-1 is present in the Golgi apparatus and within small punctate structures reminiscent of endosomes. In vitro studies suggest that SKI-1 is a Ca2+-dependent serine proteinase exhibiting a wide pH optimum for cleavage of pro-brain-derived neurotrophic factor.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Animals, Newborn
  • Cell Line
  • Female
  • Humans
  • Immunohistochemistry
  • Mammals
  • Mice
  • Molecular Sequence Data
  • Molecular Weight
  • Organ Specificity
  • Polymerase Chain Reaction
  • Proprotein Convertases*
  • Protein Precursors / metabolism
  • Protein Processing, Post-Translational
  • RNA, Messenger / genetics
  • Rats
  • Rats, Sprague-Dawley
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Saccharomyces cerevisiae Proteins*
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Substrate Specificity
  • Subtilisins / chemistry
  • Subtilisins / genetics*
  • Subtilisins / metabolism*
  • Transcription, Genetic
  • Transfection


  • Protein Precursors
  • RNA, Messenger
  • Recombinant Proteins
  • Saccharomyces cerevisiae Proteins
  • Proprotein Convertases
  • Subtilisins
  • KEX2 protein, S cerevisiae

Associated data

  • GENBANK/AF094820
  • GENBANK/AF094821