B. Wang et al., HUMAN CATHEPSIN-F - MOLECULAR-CLONING, FUNCTIONAL EXPRESSION, TISSUE LOCALIZATION, AND ENZYMATIC CHARACTERIZATION, The Journal of biological chemistry, 273(48), 1998, pp. 32000-32008
A cDNA for a novel human papain-like cysteine protease, designated cat
hepsin F, has been cloned from a lambda gt10-skeletal muscle cDNA libr
ary. The nucleotide sequence encoded a polypeptide of 302 amino acids
composed of an 88-residue propeptide and a 214-residue mature protein.
Protein sequence comparisons revealed 58% homology with cathepsin W;
about 42-43% with cathepsins L, K S, H and O; and 38% with cathepsin B
. Sequence comparisons of the propeptides indicated that cathepsin F a
nd cathepsin W may form a new cathepsin subgroup. Northern blot analys
is showed high expression levels in heart, skeletal muscle, brain, tes
tis, and ovary; moderate levels in prostate, placenta, Liver, and colo
n; and no detectable expression in peripheral leukocytes and thymus. T
he precursor polypeptide of human recombinant cathepsin F, produced in
Pichia pastoris, was processed to its active mature form autocatalyti
cally or by incubation with pepsin. Mature cathepsin F was highly acti
ve with comparable specific activities toward synthetic substrates as
reported for cathepsin L. The protease had a broad pH optimum between
5.2 and 6.8. Similar to cathepsin L, its pH stability at cytosolic pH
(7.2) was short, with a half-Life of approximately 2 min. This may sug
gest a function in an acidic cellular compartment. Transient expressio
n of T7-tagged cathepsin F in COS-7 cells revealed a vesicular distrib
ution of the gene product in the juxtanuclear region of the cells. How
ever, contrary to all known cathepsins, the open reading frame of the
cathepsin F cDNA did not encode a signal sequence, thus suggesting tha
t the protease is targeted to the lysosomal compartment via an N-termi
nal signal peptide-independent lysosomal targeting pathway.