Ng. Seidah et al., Mammalian subtilisin kexin isozyme SKI-1: A widely expressed proprotein convertase with a unique cleavage specificity and cellular localization, P NAS US, 96(4), 1999, pp. 1321-1326
Citations number
33
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Using reverse transcriptase-PCR and degenerate oligonucleotides derived fro
m the active-site residues of subtilisin/kexin-like serine proteinases, we
have identified a highly conserved and phylogenetically ancestral human, ra
t, and mouse type I membrane-bound proteinase called subtilisin/kexin isozy
me-1 (SKI-1). Computer databank searches reveal that human SKI-1 was cloned
previously but with no identified function. In situ hybridization demonstr
ates that SKI-1 mRNA is present in most tissues and cells. Cleavage specifi
city studies show that SKI-1 generates a 28-kDa product from the 32-kDa bra
in-derived neurotrophic factor pre cursor, cleaving at an RGLT down arrow S
L 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) dif
fering by the nature of their N-glycosylation. Late along the secretory pat
hway some of the membrane bound enzyme is shed into the medium as a 98-kDa
form. Immunocytochemical analysis of stably transfected HK293 cells shows t
hat SKI-1 is present in the Golgi apparatus and within small punctate struc
tures reminiscent of endosomes. In vitro studies suggest that SKI-1 is a Ca
2+-dependent serine proteinase exhibiting a wide pH optimum for cleavage of
pro-brain-derived neurotrophic factor.