Meprin is a
zinc endopeptidase of the
astacin family, which is expressed as a membrane-bound or secreted
protein in mammalian epithelial cells, in intestinal leucocytes and in certain
cancer cells. There are two types of
meprin subunits, alpha and beta, which form disulphide-bonded homo- and hetero-oligomers. Here we report on the cleavage of matrix
proteins by hmeprin (human
meprin) alpha and beta homo-oligomers, and on the interactions of these
enzymes with inhibitors. Despite their completely different cleavage specificities, both hmeprin alpha and beta are able to hydrolyse basement membrane components such as
collagen IV,
nidogen-1 and
fibronectin. However, they are inactive against intact
collagen I. Hence the matrix-cleaving activity of hmeprin resembles that of
gelatinases rather than
collagenases. Hmeprin is inhibited by
hydroxamic acid derivatives such as
batimastat,
galardin and
Pro-Leu-Gly-hydroxamate, by TAPI-0 (tumour
necrosis factor alpha
protease inhibitor-0) and
TAPI-2, and by
thiol-based compounds such as
captopril. Therapeutic targets for these inhibitors are
MMPs (matrix
metalloproteases), TACE (tumour
necrosis factor alpha-converting
enzyme) and
angiotensin-converting enzyme respectively. The most effective inhibitor of hmeprin alpha in the present study was the naturally occurring hydroxamate
actinonin ( K(i)=20 nM). The marked variance in the cleavage specificities of hmeprin alpha and beta is reflected by their interaction with the TACE inhibitor
Ro 32-7315, whose affinity for the beta subunit (IC50=1.6 mM) is weaker by three orders of magnitude than that for the alpha subunit ( K(i)=1.6 microM).
MMP inhibitors such as the
pyrimidine-2,4,6-trione derivative
Ro 28-2653 that are more specific for
gelatinases do not bind to hmeprin, presumably due to the subtle differences in the mode of
zinc binding and active-site structure between the astacins and the
MMPs.