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Identification and characterization of microtubule proteins from myxamoebae of Physarum polycephalum
Abstract:
Cell extracts of myxamoebae of Physarum polycephalum have been prepared in such a way that they do not inhibit assembly of brain microtubule protein in vitro even at high extract-protein concentration. Co-polymers of these extracts and brain tubulin have been purified to constant stoichiometry and amoebal components identified by radiolabelling. Amoebal tubulin has been identified as having an alpha-subunit, mol.wt. 54 000, which co-migrates with brain alpha-tubulin and a beta-subunit, mol.wt. 50 000, which co-migrates with Tetrahymena ciliary beta-tubulin. Non-tubulin amoebal proteins that co-purify with tubulin during co-polymer formation have been shown to be essential for microtubule formation in the absence of glycerol and appear to be rather more effective than brain microtubule-associated proteins in stimulating assembly. The mitotic inhibitor griseofulvin (7-chloro-2',4,6-trimethoxy-6'-methylspiro[benzofuran-2(3H),1'-cyclohex-2'-ene] -3,4'-dione), which binds to brain microtubule-associated proteins and inhibits brain microtubule assembly in vitro, affected co-polymer microtubule protein in a similar way, but to a slightly greater extent.
Insights
Physarum polycephalum amoebal extracts contain tubulin proteins essential for microtubule assembly. These extracts also include non-tubulin proteins that enhance microtubule formation more effectively than brain-associated proteins.
Area of Science:
- Cell biology
- Biochemistry
- Molecular biology
Background:
- Microtubules are crucial cytoskeletal components involved in various cellular processes.
- Brain tubulin is a well-studied protein essential for microtubule formation.
- Physarum polycephalum offers a unique model system for studying cellular components.
Purpose of the Study:
- To investigate the properties of microtubule proteins from Physarum polycephalum amoebae.
- To identify and characterize amoebal tubulin and associated proteins.
- To compare the assembly-promoting activity of amoebal proteins with brain microtubule-associated proteins.
Main Methods:
- Preparation of cell extracts from Physarum polycephalum myxamoebae.
- In vitro assembly of brain tubulin with amoebal extracts.
- Purification of co-polymers and identification of amoebal components via radiolabelling.
- Assessment of microtubule assembly in the presence of griseofulvin.
Main Results:
- Physarum polycephalum extracts contain alpha- and beta-tubulin subunits with molecular weights of 54,000 and 50,000, respectively.
- Non-tubulin amoebal proteins co-purify with tubulin and are essential for microtubule formation without glycerol.
- These amoebal proteins exhibit greater microtubule assembly-stimulating activity than brain microtubule-associated proteins.
- The mitotic inhibitor griseofulvin similarly affects co-polymer microtubule protein assembly, with a slightly greater effect.
Conclusions:
- Physarum polycephalum amoebae possess functional tubulin and novel proteins that facilitate microtubule assembly.
- Amoebal microtubule-associated proteins are potent stimulators of tubulin polymerization.
- These findings provide insights into the conserved and unique mechanisms of microtubule regulation across different organisms.