PubMed Journals: J Biol Chem
Source: PMID: 11115496
⇦ ⇨ J Biol Chem. 2001 Mar 16;276(11):8118-24.
⇩ Epub 2000 Dec 13.
Identification of internal autoproteolytic
cleavage sites within the prosegments of
recombinant procathepsin B and procathepsin S.
Contribution of a plausible unimolecular
autoproteolytic event for the processing
of zymogens belonging to the papain family.
Quraishi O(1), Storer AC.
(1) Protein Engineering Network of Centres
of Excellence and Department of Biochemistry,
McGill University, Montreal, Quebec H3G
The steps involved in the maturation of
proenzymes belonging to the papain family
of cysteine proteases have been difficult
to characterize. Intermolecular processing
at or near the pro/mature junction, due
either to the catalytic activity of active
enzyme or to exogeneous proteases, has been
well documented for this family of proenzymes.
In addition, kinetic studies are suggestive
of a slow unimolecular mechanism of autoactivation
which is independent of proenzyme concentration.
However, inspection of the recently determined
x-ray crystal structures does not support
this evidence. This is due primarily to
the extensive distances between the catalytic
thiolate-imidazolium ion pair and the putative
site of proteolysis near the pro/mature
junction required to form mature protein.
Furthermore, the prosegments for this family
of precursors have been shown to bind through
the substrate binding clefts in a direction
opposite to that expected for natural substrates.
We report, using cystatin C- and N-terminal
sequencing, the identification of autoproteolytic
intermediates of processing in vitro for
purified recombinant procathepsin B and procathepsin S.
Inspection of the x-ray crystal structures
reported to date indicates that these reactions
occur within a segment of the proregion
which binds through the substrate binding
clefts of the enzymes, thus suggesting that
these reactions are occurring as unimolecular
DOI: 10.1074/jbc.M005851200 PMID: 11115496
[Indexed for MEDLINE]