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Different binding kinetics of Serratia 56K protease with plasma alpha 2-macroglobulin and chicken egg white
Abstract:
We recently reported that Serratia 56K protease is inhibited by plasma alpha 2 macroglobulin (alpha 2M) temporarily and by chicken egg white ovomacroglobulin (ovoM) continuously (Molla, A. et al. (1986) Infect. Immun. 53, 522-529). The inhibition of this protease is almost complete with ovoM whereas it is incomplete with alpha 2M, although these two macroglobulins show homology and many similarities. In the present study we determined the apparent numbers of binding sites and binding constants for the two macroglobulins by means of the fluorescence polarization method using FITC-labeled 56K protease. The time courses of complex formation of 56K protease with alpha 2M and ovoM were different; with ovoM it was complete within 5 min while with alpha 2M 150 min was required. Their apparent molecular volumes were also different; the fluorescence polarization value of the E/I complex was 18.7% larger with ovoM than with alpha 2M. The association constants obtained on Scatchard plot analysis with 56K protease and alpha 2M or ovoM were 0.33 X 10(7) M-1 and 1.09 X 10(7) M-1, respectively. One molecule of each of these macroglobulins binds 1.13 and 1.35 molecules of 56K protease, respectively. Upon E/I complex formation, an increase in amino groups due to proteolysis was noted in both cases, but more progressive proteolysis was observed in the case of alpha 2M. Furthermore, when the 56K protease was inactivated through the depletion of Zn atoms, complex formation did not occur.
Insights
Ovomacroglobulin (ovoM) continuously inhibits Serratia 56K protease more effectively than alpha 2 macroglobulin (alpha 2M), with distinct binding kinetics and constants. Zinc depletion prevents protease inhibition by these macroglobulins.
Area of Science:
- Biochemistry
- Enzymology
- Protein Chemistry
Background:
- Serratia 56K protease exhibits differential inhibition by plasma alpha 2 macroglobulin (alpha 2M) and chicken egg white ovomacroglobulin (ovoM).
- While homologous, alpha 2M provides temporary and incomplete inhibition, whereas ovoM offers continuous and near-complete inhibition.
Purpose of the Study:
- To quantitatively compare the binding interactions between Serratia 56K protease and alpha 2M versus ovoM.
- To elucidate the kinetics, stoichiometry, and mechanism of protease inhibition by these two macroglobulins.
Main Methods:
- Utilized fluorescence polarization with FITC-labeled 56K protease to study complex formation with alpha 2M and ovoM.
- Determined association constants via Scatchard plot analysis.
- Investigated the role of zinc in protease activity and macroglobulin binding.
Main Results:
- Complex formation was significantly faster with ovoM (5 min) than alpha 2M (150 min).
- Apparent molecular volumes differed, with ovoM complexes showing higher fluorescence polarization.
- Association constants were 0.33 x 10^7 M-1 for alpha 2M and 1.09 x 10^7 M-1 for ovoM.
- Stoichiometry indicated binding of 1.13 and 1.35 protease molecules per macroglobulin, respectively.
- Proteolysis occurred upon complex formation, with more progressive activity observed with alpha 2M.
- Zinc depletion abolished protease-macroglobulin complex formation.
Conclusions:
- Ovomacroglobulin demonstrates superior and more rapid inhibition of Serratia 56K protease compared to alpha 2 macroglobulin.
- Differences in binding kinetics, stoichiometry, and proteolysis highlight distinct interaction mechanisms.
- Zinc is essential for the interaction between Serratia 56K protease and its inhibiting macroglobulins.