Kinesin molecular motors: transport pathways, receptors, and human disease

Abstract

Kinesin molecular motor proteins are responsible for many of the major microtubule-dependent transport pathways in neuronal and non-neuronal cells. Elucidating the transport pathways mediated by kinesins, the identity of the cargoes moved, and the nature of the proteins that link kinesin motors to cargoes are areas of intense investigation. Kinesin-II recently was found to be required for transport in motile and nonmotile cilia and flagella where it is essential for proper left-right determination in mammalian development, sensory function in ciliated neurons, and opsin transport and viability in photoreceptors. Thus, these pathways and proteins may be prominent contributors to several human diseases including ciliary dyskinesias, situs inversus, and retinitis pigmentosa. Kinesin-I is needed to move many different types of cargoes in neuronal axons. Two candidates for receptor proteins that attach kinesin-I to vesicular cargoes were recently found. One candidate, sunday driver, is proposed to both link kinesin-I to an unknown vesicular cargo and to bind and organize the mitogen-activated protein kinase components of a c-Jun N-terminal kinase signaling module. A second candidate, amyloid precursor protein, is proposed to link kinesin-I to a different, also unknown, class of axonal vesicles. The finding of a possible functional interaction between kinesin-I and amyloid precursor protein may implicate kinesin-I based transport in the development of Alzheimer's disease.

Figure 1

Schematic diagram of mammalian photoreceptor. Microtubule organization and location of major cellular organelles are shown. In the inner segment, microtubules have their minus ends located near the basal bodies; connecting cilium microtubules have their minus ends at the basal body as well. ER, endoplasmic reticulum.

Figure 2

Organization of kinesin-I. Two heavy chain components (KHC) and two light chain components (KLC) form the native heterotetramer. Proposed TPR domains are thought to mediate cargo binding via protein–protein interactions.