Understanding axonal transport processes is a key to understanding the dynamics of the nervous system, because they underlie neuronal growth, maintenance and regeneration. As a result, elucidation of molecular mechanisms for fast axonal transport can provide essential insights into the function and pathology of the nervous system. Functions as diverse as conduction of the action potential, release of neurotransmitter, creating and sustaining the presynaptic terminal, neuronal development and regeneration, and maintenance of neuronal architecture depend critically on fast axonal transport of membrane bounded organelles (MBOs) along microtubules. Similarly, disruption of fast axonal transport has been implicated in pathogenesis for a wide range of neuropathological conditions, including diabetic and toxic neuropathies, motor neuron disease (ALS and others) and degenerative diseases of the nervous system (Huntington's disease and others). Our original studies of fast axonal transport in isolated axoplasm from the squid giant axon led to discovery of a new family of mechanochemical ATPases: the kinesins. Kinesins are motors for movement of membrane bounded organelles in the anterograde direction of fast axonal transport. Previous work supported by this application answered many questions about the biochemistry and molecular biology, cell biology, and neurobiology of kinesin. Future experiments will extend our current studies on molecular mechanisms of fast axonal transport in three areas. First, we propose that physiological properties of different kinesins are determined by variation within specific functional domains among kinesin isoforms of the neuron. Studies proposed in this application combine methods from biophysics, cell biology, and molecular biology to delineate the functional architecture of neuronal kinesins and determine physiological functions for each domain. Second, specificity of kinesin interactions with different organelles suggest that kinesin isoforms are uniquely targeted to specific classes of MBOs through a combination of specific membrane receptors and general kinesin interacting proteins. Proposed experiments will identify kinesin receptors and interacting proteins in nervous tissues. Finally, kinesins are subject to posttranslational modifications in neurons that vary among the different isoforms. We propose that posttranslational modifications of kinesin serve to regulate kinesin function in neurons. Pathways associated with these modifications may control kinesin interactions with specific classes of MBOs as well as kinesin-mediated motility and ATPase activity. Planned experiments will determine the functional significance of posttranslational modifications on kinesin heavy and light chains, as well as defining relevant regulatory pathways. The proposed studies will help us understand the role of the kinesins in both normal neuronal function and neuropathology.
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