C. elegans KLP-11/OSM-3/KAP-1: Orthologs of the Sea Urchin Kinesin-II, and Mouse KIF3A/KIFB/KAP3 Kinesin Complexes

Abstract

Kinesins are intracellular multimeric transport motor proteins that move cellular cargo on microtubule tracks. It has been shown that the sea urchin KRP85/95 holoenzyme associates with a KAP115 non-motor protein, forming a heterotrimeric complex in vitro, called the Kinesin-II. Here we describe isolation of a cDNA clone corresponding to the klp-11 kinesin in C. elegans. Our sequence analysis of the encoded KLP-11 shows that it shares high homology with the OSM-3 kinesin. We also describe a nematode cDNA encoding KAP-1 that shares extensive homology with the sea urchin KAP115 kinesin associated protein. Sequence-based structural analysis of the OSM-3, KLP-11, and KAP-1, presented here suggests that these may form a heterotrimeric complex. We also describe the presence of a Drosophila armadillo consensus motif in CeKAP-1, first found in spKAP115, that suggests a possible role for the KAP-1 in signal transduction.

A Screen for Modifiers of Cilia Phenotypes Reveals Novel MKS Alleles and Uncovers a Specific Genetic Interaction between osm-3 and nphp-4

“…elegans KLP-11 mediates IFT in the proximal cilia region [ 44 ]. In contrast to our data with OSM-3, phosphorylated Fla8 (Fla8-S663D) inhibits entry of kinesin-II in the cilia, whereas unphosphorylated Fla8 (FLA8-S663A) stimulates entry [ 28 , 41 ]. Kinesin 2a (Kif2a) has recently been shown to localize to the basal body at the base of the cilium when it is not involved in the cell cycle, and when phosphorylated by another ciliary kinase, Polo-like Kinase 1, becomes activated–showing a similar behavior as we observe for OSM-3.…”

“…Ultra-structural analysis of the cilia in nphp-4(tm925);osm-3(yhw66) mutants by transmission electron microscopy (TEM) confirms that the double mutant cilia lack distal segments while maintaining normally formed middle segments ( Fig 3E ). This is similar to what is seen in osm-3(mn357) null mutants [ 28 , 29 , 34 ]. Osm-3(yhw66) single mutants were also analyzed; and have properly formed distal segments ( Fig 3E ).…”

“…elegans there are two IFT kinesin complexes in cilia with Osm-3 being the only kinesin that functions on microtubule singlets of the cilium’s distal segment [ 28 – 31 ]. As a consequence, in osm-3(mn357) null mutants the proximal region of cilia form while the distal segments do not, resulting in a Dyf phenotype [ 28 , 32 , 33 ]. In the nphp-4(tm925);osm-3(yhw66 ) mutants obtained from the screen the distal segments of cilia appear to be absent and they have a severe Dyf phenotype (Figs 1C and 3D and 3E ) closely resembling osm-3(mn357) null mutants.…”

Intraflagellar Transport

“…Initially OSM-3 was thought to be a subunit of a heterotrimeric kinesin-II (Wedaman et al 1996, Cole et al 1998, Khan et al 2000, but careful fractionation experiments showed that it is a subunit of a distinct homodimeric complex, whose two N-terminal motor domains are predicted to be linked by a 26-nm coiled-coil rod to a short tail (Signor et al 1999b). Perhaps, homodimeric kinesin-II transports a cargo distinct from that transported by heterotrimeric kinesin-II, but the functional relationship between these motors is unknown.…”

The Intraflagellar Transport Machinery of Chlamydomonas reinhardtii

“…This was not necessarily expected because some lower organisms are known to have two distinct kinesin‐II complexes operating in their cilia. The best characterized of these is Caenorhabditis elegans where CeKRP85, CeKRP95 and CeKAP combine to form a heterotrimeric complex analogous to the Chlamydomonas FLA10/FLA10H/CrKAP complex (39,40). C. elegans also expresses OSM‐3 (41), a third kinesin‐II motor protein, which is required for ciliary assembly (42) and appears to homodimerize with itself but does not associate with CeKRP85, CeKRP95 or CeKAP (39).…”