Cilia are microtubule-based protrusions of the plasma membrane found on most eukaryotic cells. The construction and maintenance of cilia relies on an ancient, universally conserved mechansim termed Intraflagellar Transport (IFT). IFT requires a multi-subunit, non-membranous protein complex assembled from more than 20 distinct subunits. At the heart of IFT are the microtubule-associated motors, kinesin and dynein that continuously drive the transport to the tip and base of the cilium. We focus on the complex assembly and transport process of IFT in the nematode C. elegans. Our goal is to reconstruct the multi-component IFT complex in a bottom-up approach. Employing structural, biochemical and biophysical methods, we analyze the architecture of the complex as well as its kinesin-driven transport powered by the two distinct kinesin-2 motors KLP11/KLP20 and OSM-3.
Regulation of heterodimeric kinesin-2 through an unprocessive motor domain
One class of motor proteins involved in intraflagellar transport, kinesin-2, is unique among kinesin motors in that some of its members are composed of two distinct catalytic polypeptides. However, the biological reason for heterodimerization has remained elusive. We provide several interdependent reasons for the heterodimerization of the kinesin-2 motor KLP11/KLP20 of Caenorhabditis elegans. One motor domain is unprocessive as a homodimer, but heterodimerization with a processive partner generates processivity. The "unprocessive" subunit is kept in this partnership as it mediates an asymmetric autoregulation of the motor activity. Finally, heterodimerization is necessary to bind KAP1, the in vivo link between motor and cargo. pdf