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The specific binding of the microtubule-associated protein 2 (MAP2) to the outer membrane of rat brain mitochondria
M Lindén1, B D Nelson, J F Leterrier
1Arrhenius Laboratory, Institute of Biochemistry, Stockholm University, Sweden.
Abstract:
Purified mitochondria from rat brain contain microtubule-associated proteins (MAPs) bound to the outer membrane. Studies of binding in vitro performed with microtubules and with purified microtubule proteins showed that mitochondria preferentially interact with the high-molecular-mass MAPs (and not with Tau protein). Incubation of intact mitochondria with Taxol-stabilized microtubules resulted in the selective trapping of both MAPs 1 and 2 on mitochondria, indicating that an interaction between the two organelles occurred through a site on the arm-like projection of MAPs. Two MAP-binding sites were located on intact mitochondria. The lower-affinity MAP2-binding site (Kd = 2 x 10(-7) M) was preserved and enriched in the outer-membrane fraction, whereas the higher-affinity site (Kd = 1 x 10(-9) M) was destroyed after removing the outer membrane with digitonin. Detergent fractionation of mitochondrial outer membranes saturated with MAP2 bound in vitro showed that MAPs are associated with membrane fragments which contain the pore-forming protein (porin). MAP2 also partially prevents the solubilization of porin from outer membrane, indicating a MAP-induced change in the membrane environment of porin. These observations demonstrate the presence of specific MAP-binding sites on the outer membrane, suggesting an association between porin and the membrane domain involved in the cross-linkage between microtubules and mitochondria.
Insights
Brain mitochondria bind microtubule-associated proteins (MAPs) via specific outer membrane sites. This interaction, involving MAPs 1 and 2, suggests a link between microtubules and mitochondria mediated by porin.
Area of Science:
- Cell Biology
- Neuroscience
- Biochemistry
Background:
- Microtubule-associated proteins (MAPs) are crucial for microtubule stability and function.
- Mitochondria play vital roles in cellular energy production and signaling.
- The interaction between cytoskeletal elements and organelles is essential for cellular organization.
Purpose of the Study:
- To investigate the binding of MAPs to rat brain mitochondria.
- To identify the specific MAPs and mitochondrial components involved in this interaction.
- To elucidate the functional implications of MAP-mitochondria association.
Main Methods:
- In vitro binding assays using purified microtubules, microtubule proteins, and rat brain mitochondria.
- Differential extraction and fractionation of mitochondrial membranes.
- Characterization of MAP-binding sites and their affinity.
- Analysis of the role of porin in MAP binding.
Main Results:
- Mitochondria preferentially bind high-molecular-mass MAPs, specifically MAPs 1 and 2, not Tau protein.
- Two distinct MAP-binding sites were identified on mitochondria: a high-affinity site on the inner membrane and a lower-affinity site on the outer membrane.
- The outer membrane MAP2-binding site is associated with porin, a pore-forming protein.
- MAP2 binding influences the membrane environment of porin, suggesting a cross-linking role.
Conclusions:
- Rat brain mitochondria possess specific binding sites for MAPs on their outer membrane.
- This interaction is mediated by porin and involves high-molecular-mass MAPs.
- The findings suggest a mechanism for cross-linking microtubules and mitochondria, potentially impacting mitochondrial function and cellular organization.