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Changes in trypsin-binding properties and conformation of rabbit alpha-2-macroglobulin on reaction with methylamine
1Department of Biochemistry, Faculty of Pharmacy, Kinki University, Higashi-Osaka.
Abstract:
Reactions of rabbit alpha-2-macroglobulin with methylamine and trypsin were studied and the results were compared with those obtained for previously described 2-macroglobulins from other species. Rabbit alpha-2-macroglobulin was cleaved by trypsin at a number of sites, whereas the human homologue was split essentially only in the "bait" region into two fragments of similar sizes. Reaction of native or methylamine-treated rabbit alpha-2-macroglobulin with trypsin resulted in a substantial decrease in the intensity of fluorescence induced by binding of 6-(p-toluidino)-2-naphthalenesulfonate or bis(8-anilino-1-naphthalenesulfonate). Under the same conditions, the fluorescence of the human protein increased. The time course of the reaction of rabbit alpha-2-macroglobulin with methylamine was studied by measuring (i) the generation of thiol groups, (ii) the decrease in trypsin-inhibiting activity with remazol brilliant blue hide powder as the substrate, and (iii) the decrease in trypsin-protein amidase activity. The thiol appearance reaction exhibited a multiphasic time course. The initial phase was found to follow second-order kinetics with an apparent rate constant of 1.2 M-1.s-1. Under the same conditions, the human protein showed monophasic kinetics with a rate constant of 12 M-1.s-1. Both the trypsin-inhibiting activity and the trypsin-protein amidase activity concurrently decreased at a slower rate than the thiol appearance. These results indicate that rabbit alpha-2-macroglobulin is more stable to nucleophilic attack by methylamine but less resistant to proteolysis by trypsin than the human homologue, and that the final conformation induced by methylamine differs considerably from that induced by trypsin.
Insights
Rabbit alpha-2-macroglobulin shows distinct reactions to methylamine and trypsin compared to its human counterpart. It is more stable to methylamine but less resistant to trypsin, with conformational changes differing significantly between reactions.
Area of Science:
- Biochemistry
- Proteomics
- Comparative protein analysis
Background:
- Alpha-2-macroglobulin (α2M) is a large plasma proteinase inhibitor.
- Understanding species-specific reactions of α2M provides insights into protein structure-function relationships.
Purpose of the Study:
- To compare the reactions of rabbit alpha-2-macroglobulin with methylamine and trypsin to those of human alpha-2-macroglobulin.
- To elucidate the kinetic and conformational differences in these reactions.
Main Methods:
- Studied reactions using methylamine and trypsin.
- Monitored changes in fluorescence intensity upon ligand binding.
- Quantified thiol group generation and trypsin-inhibiting activity.
- Analyzed reaction kinetics and protein cleavage sites.
Main Results:
- Rabbit α2M cleaved by trypsin at multiple sites, unlike human α2M which splits mainly in the bait region.
- Trypsin-induced fluorescence changes differed significantly between rabbit and human α2M.
- Rabbit α2M exhibited multiphasic thiol generation with a slower rate constant (1.2 M-1.s-1) compared to human α2M (12 M-1.s-1).
- Trypsin-inhibiting and amidase activities decreased slower than thiol appearance in rabbit α2M.
Conclusions:
- Rabbit α2M is more stable to methylamine and less resistant to trypsin proteolysis than human α2M.
- Methylamine and trypsin induce distinct final conformations in rabbit α2M.
- Species-specific differences in α2M reactivity highlight the importance of protein structure in function.