Conformation and protease
binding activity of binary and ternary human alpha
2-macroglobulin-protease complexes.
Gonias SL, Pizzo SV.
Conformation and protease binding activity of binary and
ternary human alpha
Human alpha 2-macroglobulin (alpha 2M) undergoes a conformational
change after reaction with proteases. In this report, it is shown
that although two trypsin molecules may bind simultaneously to each
alpha 2M, only one trypsin is necessary to induce alpha 2M
conformational change. Ternary complexes of alpha 2M and either two
radioiodinated trypsins or two nonradioiodinated trypsins were
purified by gel filtration chromatography. The nonradioactive
complex did not bind 125I-trypsin, even after incubation for 24 h
with the free protease present
at a large molar excess. Under comparable conditions, a large
molar excess of nonradioactive trypsin did not cause significant
dissociation of the complex prepared with radioiodinated protease.
Equations are presented that distinguish between two separate models
of protease binding and demonstrate that binary alpha 2M-trypsin
complex retains no significant trypsin binding activity despite the
presence of a vacant protease binding site. Purified alpha
2M-plasmin complex, with 1.10 mol of plasmin/mol of inhibitor, also
retained no trypsin binding activity as assessed with radioiodinated
protein binding experiments. These studies suggest that reactions of
alpha 2M with proteases are accurately described by the "trap
hypothesis" (Barrett, A. J., and Starkey, P. M. (1973) Biochem. J.
133, 709-724) independent of protease size or binding stoichiometry.
Comment:
The confirmation change of alpha-2-macroglobulin due to protease
interaction is well documented and understood. When we consider how
the conformation change results in “activated alpha-2-macroglobulin”
and that the activated form binds cytokines, damaged proteins and
other molecular debris, we can fully appreciate the actions of
Wobenzym® N.