Related Experiment Videos
The possible self-down-regulation of calpain triggered by cell membranes
1Department of Enzyme Biochemistry, Tokyo Metropolitan Institute of Gerontology, Japan.
Abstract:
In order to confirm whether the binding sites for mu-calpain on the inner surface of erythrocyte membranes are substrate proteins themselves, we examined the binding properties of mu-calpain to mu-calpain-pretreated inside-out membranes. When native mu-calpain was incubated with mu-calpain-pretreated membranes, however, newly added calpain was degraded rapidly in a time- and Ca(2+)-dependent manner. Although the degradation of mu-calpain was not inhibited by various proteinase inhibitors, it was strongly inhibited by digestible substrates for calpain that possess the ability to inhibit the binding of mu-calpain to erythrocyte membranes. On the other hand, when mu-calpain inactivated by N-ethylmaleimide was incubated with mu-calpain-pretreated membranes, no degradation was observed. These results indicate that the degradation of mu-calpain occurs on the surface of mu-calpain-modified membranes and that it depends on the autoproteolytic activity of mu-calpain itself. It seems likely that the autoproteolytic activity of mu-calpain is accelerated markedly by some component(s) exposed on the surface of membranes during the pretreatment with mu-calpain. The possibility is thus proposed that cell membranes possess the ability to down-regulate calpain to protect cell membranes from overdegradation by excessively bound calpain. The active factor(s) in the membranes that can accelerate the autoproteolytic degradation of mu-calpain could be almost completely removed from mu-calpain-modified membranes by treatment with Triton X-100.
Insights
Erythrocyte membranes can degrade bound mu-calpain (calcium-dependent protease) via autoproteolysis. This self-degradation is accelerated by membrane components, potentially protecting cells from excessive protease activity.
Area of Science:
- Biochemistry
- Cell Biology
- Proteolysis
Background:
- Mu-calpain is a calcium-dependent protease implicated in various cellular processes.
- The interaction of mu-calpain with erythrocyte membranes is not fully understood.
- Investigating the binding sites and functional consequences of mu-calpain interaction with membranes is crucial.
Purpose of the Study:
- To determine if mu-calpain binding sites on erythrocyte membranes are substrate proteins.
- To investigate the fate of mu-calpain bound to erythrocyte membranes.
- To explore the role of membrane components in modulating mu-calpain activity.
Main Methods:
- Incubation of native and inactivated mu-calpain with erythrocyte membranes pretreated with mu-calpain.
- Assessment of mu-calpain degradation in a time- and calcium-dependent manner.
- Use of proteinase inhibitors and calpain substrates to analyze degradation pathways.
- Treatment of membranes with Triton X-100 to identify active factors.
Main Results:
- Native mu-calpain bound to pretreated membranes undergoes rapid, calcium-dependent degradation.
- Degradation is inhibited by calpain substrates but not by general proteinase inhibitors.
- Inactivated mu-calpain does not degrade on the membranes, indicating autoproteolysis is responsible.
- Membrane components, removable by Triton X-100, accelerate mu-calpain autoproteolysis.
Conclusions:
- Erythrocyte membranes possess components that accelerate mu-calpain autoproteolysis.
- This accelerated degradation suggests a self-regulatory mechanism to prevent overdegradation of cell membranes by bound calpain.
- Cell membranes may actively down-regulate calpain activity through induced autoproteolysis.