Microtubules Microtubule-based motor proteins

Microtubule-Based Motor Proteins The Meiotic and Mitotic Spindles Microfilament-Based Intracellular Motility Cytokinesis... 

Zhu, C., Zhao, J., Bibikova, M., Leverson, J. D., Bossy-Wetzel, E., Fan, J. B., Abraham, R. T, Jiang, W. Functional analysis of human microtubule-based motor proteins, the kinesins and dyneins, in mitosis/... 

MAPs can be classified in a similar manner to actin-binding proteins. Like their actin-binding counterparts, MAPs can nucleate, cap, stabilize and cross-link microtubules. Several motor proteins have been identified in the last few years which are involved in force generation in a number of microtubule-based networks. As with actin-binding proteins, MAPs can be targeted, on a constitutive or transient basis, to certain regions of a cell. This allows specialized microtubule-based networks to be constructed and perform their tasks in specific locations. The properties and functions of some of these MAPs will be explored in the examples given below. 

Just as myosins are able to move along microfilaments, there are motor proteins that move along microtubules. Microtubules, like microfilaments, are polar polymeric assemblies, but unlike actin-myosin interactions, microtubule-based motors exist that move along microtubules in either direction. A constant traffic of vesicles and organelles is visible in cultured cells especially using time-lapse photography. The larger part of this movement takes place on micrombules and is stimulated by phorbol ester (an activator of protein kinase C), and over-expression of N-J aj oncoprotein (Alexandrova et al., 1993). 

Dynein Motor protein mediating microtubule-based synaptic vesicle transport. May be involved in retrograde axonal transport to the cell body. 

Kinesins Motor proteins for microtubule-based synaptic vesicle transport. In Caenorhabditis elegans, akinesin encoded by unc-104 is essential for transport of synaptic vesicles to nerve terminals. 

Myosins are actin-based motors (see Chapter 5). The reason for considering myosin in the context of microtubule motors is that the catalytic domains of myosin and kinesin share structural similarities indicating that both families use a similar mechanism for energy conversion. The structural relationship between these families suggests that both descend from a common ancestor, a primordial nucleotide binding protein (Kull et ah, 1998). 

In this section, we first consider the transport of materials In axons. Studies of such axonal transport, a process first discovered more than 50 years ago, have contributed greatly to our understanding of microtubule-associated Intracellular transport. We then consider the structure and function of the microtubule motor proteins. A description of the unique microtubule-based structures and motor proteins responsible for the movement of cilia and flagella concludes this section. 

Moore, J. D., and S. A. Endow. 1996. Kinesin proteins a phylum of motors for microtubule-based motility. Bioessays 18 207-218. 

To establish and maintain such complex and elongated architecture, neurons employ cytoskeletal motor proteins to drive active transport of cellular building blocks to specific destinations. These motor proteins can move directionally along either of two types of cytoskeletal biopolymers actin filaments and microtubules (MTs). Actin facilitates motility of motor proteins of the myosin superfamily, whereas MTs serve as tracks for two families of motor proteins, kinesin and dynein, which move in opposite directions along the MTs. In neurons, long range transport is predominandy microtubule-based. 

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