3/12/26 Molecular Motors, Kinesin, and Intermediate Filaments

Introduction of kinesin as a molecular motor.
Description of fluorescent microtubule with bundled microtubules.
- Kinesin motors attached to glass surface that walk along microtubules.
- Motor heads generating force to move microtubule in a process called microtubule gliding assay.
Analogy comparing kinesin walking on microtubules to crowd surfing.

Bidirectional Trafficking: Refers to the ability of motors like kinesin (plus end-directed) and dynein (minus end-directed) to transport cargo in opposite directions.
Kinesin: Plus-end directed motor protein critical for moving cargo like vesicles and organelles toward cell periphery.
- Kinesin heads bind to tubulin and walk down microtubules using energy from ATP hydrolysis.
- Emphasis on ATP hydrolysis, conformational changes, and force generation.

Dynein: Microtubule motor that functions by moving cargo toward the minus end.
- Offers flexibility by stepping over obstacles on microtubules, allowing for traffic management with other motors.

Numerous related motor proteins exist.
- Kinesins: 45 related genes, not just Kinesin 1 – indicate gene duplication and specialization for different cellular functions.
- Dyneins: 24 genes with only two being cytoplasmic, others involved in specialized structures (e.g., cilia/flagella).
Myosins: Associated with actin fibers, number of related genes is also significant.

Importance of understanding how motors transport specific cargoes effectively within the cell rather than through random diffusion.
Kinesin is involved in trafficking various organelles within cells, including vesicles and mitochondria.

Kinesin structure: Dimer with two motor heads and a flexible neck linker for efficient movement.
Each step taken is about 8 nanometers, coinciding with the length of tubulin heterodimers (alpha and beta).
The concept of processivity in molecular motors: staying bound to microtubule for sustained movement.

Animation illustrating the kinetics of kinesin walking along microtubules.
- Interaction with microtubules involving binding of heads, release of ADP, and uptake of ATP.
Clarifying common misconceptions regarding the role of ATP hydrolysis in inducing conformational changes in kinesin.

Example of a wild type mouse versus one with a kinesin mutation, showing severe motility defects due to altered kinesin functionality.
Dimeric nature of kinesin means that mutation of one allele affects overall function since they dimerize with wild type.

Representation of fluorescent microtubules with attached kinesin heads fixed to a glass surface.
- Microtubules glide as kinesin moves towards the plus end, demonstrating principles of kinesin function.

Dynein assists with cargo transport in the opposite direction. Regulation of motor engagement is crucial in cellular transport.
- Adaptation between kinesin and dynein for effective transport systems in cells.

Transition to intermediate filaments as structures providing tensile strength and stability for cells.
Differences from microtubules and actin: not nucleotide dependent, lack polarity, and no motor proteins identified for movement.

Key roles in cell adhesion, particularly in epithelial cells where disruption may lead to cancer.
Diverse types, including keratin and vimentin, influencing cell integrity and protection of the nucleus.

Formation of intermediate filaments is distinct: dimers forming tetramers with non-polar ends and allowing lateral interactions.
Unique dynamic assembly pathway allowing internal exchange of subunits (intercalation).

Intermediate filaments' role in the nuclear lamina supports DNA integrity and its disassembly during mitosis regulated by phosphorylation.
Observations of nuclear lamina dynamics and its recovery post-mitosis demonstrated through imaging techniques.

Discussion on point mutations in lamins leading to various human diseases, especially focusing on our understanding of their importance in cellular structure and function.