Ch. Bu et T. Pourmotabbed, MECHANISM OF ACTIVATION OF HUMAN NEUTROPHIL GELATINASE-B - DISCRIMINATING BETWEEN THE ROLE OF CA2+ IN ACTIVATION AND CATALYSIS, The Journal of biological chemistry, 270(31), 1995, pp. 18563-18569
Gelatinase B is a Zn2+- and Ca2+ dependent endopeptidase that is secre
ted from cells as an inactive proenzyme. The enzyme can be activated i
n vitro by organomercurial compounds and by trypsin. The role of Ca2in autoproteolytic processing initiated by 4-aminophenylmercuric aceta
te and trypsin and in catalytic activity of the activated enzyme was i
nvestigated by zymography and by kinetic analysis. Treatment of unglyc
osylated 57.5-kDa pro-gelatinase B with 4-aminophenylmercuric acetate
(1 mM) in the absence of Ca2+ generated a 49-kDa inactive intermediate
(E'), whereas a 41.5-kDa active species (E '') was generated in the p
resence of Ca2+ (5 mM). Upon addition of Ca2+ to the reaction mixture
of Ca2+ depleted E' or E '' at 37 degrees C, E' showed a lag period in
generation of the product as a function of time, but E '' presented a
n immediate activity. The appearance of enzymatic activity of E' corre
lated with the generation of the E '' species. NH2-terminal sequence a
nalyses showed that E' and E '' had the same NH2 termini. i.e. Met-75,
suggesting that Ca2+-dependent removal of COOH terminus of E' is requ
ired for activation of the enzyme, Treatment of pro-gelatinase B with
trypsin in the absence of Ca2+, led to degradation of the enzyme, In t
he presence of Ca2+, trypsin processed the pro enzyme to a 40-kDa acti
ve species. In contrast to E '', this active species did not require C
a2+ for activity. The Ca2+ dependence of E '' activity was also abolis
hed by treatment of the enzyme with trypsin. NH2-terminal sequence ana
lysis indicated that amino acid residues 75-87 had been re moved from
the NH2 terminus of E '' by trypsin, suggesting that these residues ar
e responsible for the Ca2+-dependent activity of the enzyme. Removal o
f Ca2+ and catalytic Zn2+ inhibited the activities of both E '' and tr
ypsin treated E ''. In the absence of Ca2+, either Zn2+, Co2+, Mn2+, o
r Cd2+ was able to restore the activity of trypsin-treated E ''. None
of the divalent cations tested however, was able to stimulate the acti
vity of E '' in the absence of Ca2+. These experiments further suggest
that binding of Ca2+ to E '' or removal of the NH2-terminal residues
of the enzyme by trypsin induces a conformational change in the protei
n and makes the active site of the enzyme accessible to various metal
ions rendering the enzyme active.