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***What are the major types of microtubular structures in cells and what are their functions?
- Since the 60s and 70s (Ab staining):
- 1. Spindle apparatus, centrosome and centrioles: segregating chromosomes to opposite poles during division
- 2. Interphase microtubule array: Intracellular movement, organelle movement, cell STRUCTURE.
- 3. Cilia and Flagella: cell movement
What are the major classes of tubulin proteins in eukaryotic cells and what are their primary functions?
- Alpha and beta tubulins: involved in formation of MTs, provide stability for microtubules, first forming protofilaments (13 protofilaments per microtubule)
- Gamma tubulin: important part of gamma TuRC - centrosome organizing center (MTOC)
- Other tubulins: component of centrioles and basal bodies
- FtsZ: bacterial tubulin that forms polymers for cytokinesis
What is the functional subunit for assembly of microtubules?
Alpha and beta tubulins form heterodimers: Alpha (-) has NON-exchangable GTP, beta (+) has EXCHANGABLE GTP. One dimer is positive end and can undergo GTP exchange, while the other is the negative end and does not undergo GTP exchange. In vivo minus end does NO assembly or disassembly, but in vitro it does a bit, still not as much as positive end
Tubulin gene families differ from actin gene families in that the different family members show very distinct spatial and temporal patterns of expression. How does this relate to microtubule/ microfilament function?
- Alpha and beta tubulins have different isoforms that undergo different gene expression. These isoforms have various functions:
- Ie: D. melanogaster has 4 beta genes:
- b1: ubiq, essential
- b2: male specif, resp for sperm tail
- b3: developmental related in embryonic stages
- b4: expressed at low levels
- Actin families produce Nearly IDENTICAL actin, fairly universal and ubiquitous, expressing at all times.
What are the major classes of tubulin binding proteins and what are their functions?
- 1. Binding & stabilizing: Tau, MAPs (2&4). All heat stable so can be boiled in lab to isolate
- 2. Destabilizing:
- Op18/stathmin: binds to tubulin dimers & affects shape of microtubule to destabilize
- Katanin: AAA ATPase acts to severe microtubules
- XKCM, MCAK: Kinesin related, destabilize the PLUS end
- 3. Surfacing MAPS:
- CLIP170 and EB1: link membrane to + end