Regulation of a heterodimeric kinesin-2 through an unprocessive motor domain that is turned processive by its partner

Abstract

Cilia are microtubule-based protrusions of the plasma membrane found on most eukaryotic cells. Their assembly is mediated through the conserved intraflagellar transport mechanism. 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 polypeptides. However, the biological reason for heterodimerization has remained elusive. Here we provide several interdependent reasons for the heterodimerization of the kinesin-2 motor KLP11/KLP20 of Caenorhabditis elegans cilia. 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.

Processivity of the Kinesin-2 KIF3A Results from Rear Head Gating and Not Front Head Gating

“…a, distribution of run lengths from 1000 simulated runs at 1 mM ATP. A monoexponential fit to the distribution yielded a mean run length of 470 Ϯ 9 nm, matching previous single-molecule results (19). b, distribution of single-molecule velocities, with mean Ϯ S.D.…”

“…Kinesin-1 is highly processive, taking 100 or more steps before detaching (17), which results from tight coordination between the hydrolysis cycles of the two heads. Compared with kinesin-1, kinesin-2 shows a similar stall force, a velocity roughly half of kinesin-1, and run lengths of roughly one-fourth of kinesin-1 (18,19), implying less head-head coordination.…”

Kinesin-2 KIF3AB Exhibits Novel ATPase Characteristics

“…Chimeric motors using the kinesin-1 kinesin heavy chain rod domain with chimeric M. musculus KIF3AA motor heads demonstrated that processivity scaled inversely with increased neck linker length (26). In contrast, single molecule studies using the Caenorhabditis elegans KIF3AB homolog, KLP20/KLP11, found homodimeric KLP11 (KIF3B) to be unprocessive, yet heterodimeric KLP20/KLP11 was processive (27). These results showed that heterodimerization was required for processivity and clearly documented the influence of KLP20 on KLP11.…”

Kinesin-2 heterodimerization alters entry into a processive run along the microtubule but not stepping within the run

“…In contrast, there is not strong evidence that mammalian KIF3AC binds KAP, and KIF3C lacks the sequence similarity to KIF3AB at the putative C-terminal KAP binding region (2,11,14,24). In spite of similarities in sequence and structure, KIF3AC appears to function specifically in neurons whereas heterotrimeric KIF3AB-KAP is more ubiquitously expressed and transports ciliary IFT particles, melanosomes, and organelles as well as cell signaling and cell adhesion molecules (21,23,(25)(26)(27)(28)(29)(30)(31)(32).…”

“…KIF3AB-KAP transports multimeric protein complexes (designated intraflagellar transport (IFT) particles) into the cilium and has also been linked to ciliadependent signal transduction pathways including the Hedgehog signaling pathway (16,17). Moreover, KIF3A, KIF3B, and KAP are all essential genes (18)(19)(20)(21)(22)(23), and the transport role of KIF3AB-KAP in ciliogenesis is considered the reason that KIF3AB-KAP is essential for development and the basis of similarity with other heterotrimeric kinesin-2 motor proteins.In contrast, there is not strong evidence that mammalian KIF3AC binds KAP, and KIF3C lacks the sequence similarity to KIF3AB at the putative C-terminal KAP binding region (2,11,14,24). In spite of similarities in sequence and structure, KIF3AC appears to function specifically in neurons whereas heterotrimeric KIF3AB-KAP is more ubiquitously expressed and transports ciliary IFT particles, melanosomes, and organelles as well as cell signaling and cell adhesion molecules (21,23,(25)(26)(27)(28)(29)(30)(31)(32).…”