By the end of this session, students should be able to describe the structure and function of microtubules, differentiate between dynein and kinesin motor proteins, and apply clinical correlations involving microtubule-targeting drugs and pathogen transport mechanisms.
Overview of Microtubule Structure
| Feature |
Description |
| Shape |
Cylindrical outer structure |
| Subunits |
Helical array of α- and β-tubulin heterodimers |
| Energy Source |
Each dimer binds 2 GTP molecules |
| Orientation |
Negative (-) end near the nucleus; Positive (+) end extends to the cell periphery |
| Functions |
An integral part of cilia, flagella, and the mitotic spindle; essential for axoplasmic transport in neurons |
Motor Proteins: Dynein vs Kinesin
| Motor Protein |
Direction of Transport |
Function/Notes |
| Dynein |
Retrograde (+ → −) |
Moves material toward the nucleus; used by certain viruses for retrograde axonal transport |
| Kinesin |
Anterograde (− → +) |
Moves material away from the nucleus toward the periphery; used in HSV reactivation and axonal repair |
Clinical Correlations
- Viral Transport
- Clostridium tetani toxin, poliovirus, rabies virus, and HSV utilize dynein for retrograde transport to neuronal cell bodies.
- HSV reactivation occurs via kinesin-mediated anterograde transport.
- Peripheral Nerve Regeneration
- Slow anterograde transport is the rate-limiting step in nerve regeneration after injury.
Drugs That Disrupt Microtubules
| Drug |
Category |
Clinical Use |
| Mebendazole |
Antihelminthic |
Parasitic infections |
| Griseofulvin |
Antifungal |
Dermatophyte infections |
| Colchicine |
Antigout |
Acute gout flares |
| Vinca alkaloids (e.g., vincristine, vinblastine) |
Anticancer |
Mitotic inhibitor |
| Taxanes (e.g., paclitaxel) |
Anticancer |
Stabilize microtubules; prevent depolymerization |
Key Points Summary
- Microtubules are GTP-dependent cytoskeletal structures.
- Dynein: retrograde transport; Kinesin: anterograde transport.
- Many viruses hijack dynein for neuronal invasion.
- Drugs targeting microtubules are used in cancer, gout, and parasitic infections.
🎯Activity
