PubMed Journals: Eur J Biochem
Source: PMID: 11422372
⇦ ⇨ Eur J Biochem. 2001 Jun;268(12):3423-31.
Proteolytic processing of a human salivary
proline-rich protein precursor by proprotein
Chan M(1), Bennick A.
(1) Department of Biochemistry,
University of Toronto, Toronto, Canada.
Salivary proline-rich proteins (PRPs) are
synthesized as precursors that are cleaved
before secretion giving rise to glycosylated
PRPs which have lubricating function and
basic PRPs which are potent precipitators
of dietary tannins. The putative cleavage
sites in the precursors for basic and glycosylated
PRPs all conform to the sequence RSXR downward
arrowS (X can be A, S or P) in agreement
with the recognition sequence (RXXR downward
arrow) for various proprotein convertases.
PRB4S, a proprotein giving rise to a basic
PRP (IB-5) as well as a glycosylated PRP
(II-1) was synthesized by in vitro
transcription-translation. It was cleaved
by furin at RSAR downward arrowS(173-178)
giving rise to two proteins II-1 and IB-5.
Similarly another precursor with the sequence
RSAR downward arrowS(173-178) was also cleaved
by furin. This together with previous results
show that in vitro furin can cleave all
RSXR downward arrowS sequences in the proproteins
that give rise to glycosylated and basic
PRPs. To demonstrate cellular cleavage,
a human submandibular cell line (HSG) was
transfected with a vector encoding PRB4S.
This resulted in secretion of II-1 and IB-5.
The degree of cleavage was enhanced by coexpressing
furin and PRB4S. No cleavage occurred if
the cells expressed a mutant PRB4S, R177Q,
where the furin cleavage site had been destroyed.
Cleavage was also inhibited if a furin inhibitor
was coexpressed with PRB4S. Incubating the
cells at 20 degrees C which blocks exit
of proteins from the trans-Golgi network
demonstrated that cleavage occurs before
exit of the proteins from this network.
These results show that furin may be responsible
for in vivo cleavage of PRP precursors.
Transfecting furin-deficient RPE.40 cells with
a vector encoding PRB4S also led to secretion
of II-1 and IB-5 showing that convertases
other than furin can also cleave PRB4S in
PMID: 11422372 [Indexed for MEDLINE]