Motor-Cargo Interactions Involved in Transport of Synaptic Proteins

1. Summary

Intracellular transport is fundamental for synaptogenesis, neuronal transmission, and synaptic plasticity. Proteins destined for the presynaptic active zone or the postsynaptic specialization are selectively transported to either axons or dendrites. In addition, certain mRNAs are transported for local protein synthesis. Molecular motors of the kinesin, dynein, and myosin superfamily mediate cargo recruitment along cytoskeletal elements: microtubules and actin filaments. Each motor participates in a transport complex typically consisting of a heavy chain combined with accessory light chains. Directionality of transport requires mechanisms that mediate both the recognition of individual tracks and cargoes as well as the sorting of transport complexes to specific subcellular compartments. Depending on the cargoes involved, both selective transport and selective retention have been described. A number of motor-cargo adaptors, which mediate transport specificity at intracellular sites, also locate at postsynaptic densities of mature synapses, where they participate in neurotransmitter receptor-scaffold interactions. Upon delivery to the neuronal surface, receptors enter the plasma membrane at extrasynaptic sites, followed by lateral diffusion and/or active transport between extrasynaptic and synaptic sites. The delivery and the removal of receptors that are available for synaptic transmission at a certain time are thought to participate in the regulation of synaptic strength.