Purification of novel kinesins from embryonic systems

Determination of Transglutaminase Activity in Plants

Transglutaminase (TGase:E.C. 2.3.2.13) catalyzes the acyl-transfer reaction between one or two primary amino groups of polyamines and protein-bound Gln residues giving rise to post-translational modifications. One increasing the positive charge on a proteins surface and the other results in the covalent crosslinking of proteins. Pioneering studies on TGase in plants started in the middle of the 1980's but the methodology designed for use with animal extracts was not directly applicable to plant extracts. Here we describe radioactive and colorimetric methods adapted to study plant TGase, as well as protocols to analyze the involvement of TGase and polyamines in the functionality of cytoskeletal proteins.

Purification and assay of mitotic motors

To understand how mitotic kinesins contribute to the assembly and function of the mitotic spindle, we need to purify these motors and analyze their biochemical and ultrastructural properties. Here we briefly review our use of microtubule (MT) affinity and biochemical fractionation to obtain information about the oligomeric state of native mitotic kinesin holoenzymes from eggs and early embryos. We then detail the methods we use to purify full length recombinant Drosophila embryo mitotic kinesins, using the baculovirus expression system, in sufficient yields for detailed in vitro assays. These two approaches provide complementary biochemical information on the basic properties of these key mitotic proteins, and permit assays of critical motor activities, such as MT-MT crosslinking and sliding, that are not revealed by assaying motor domain subfragments.

Fractionation and characterization of kinesin II species in vertebrate brain

Recent research on kinesin motors has outlined the diversity of the superfamily and defined specific cargoes moved by kinesin family (KIF) members. Owing to the difficulty of purifying large amounts of native motors, much of this work has relied on recombinant proteins expressed in vitro. This approach does not allow ready determination of the complement of kinesin motors present in a given tissue, the relative amounts of different motors, or comparison of their native activities. To address these questions, we isolated nucleotide-dependent, microtubule-binding proteins from 13-day chick embryo brain. Proteins were enriched by microtubule affinity purification, then subjected to velocity sedimentation to separate the 20S dynein/dynactin pool from a slower sedimenting KIF containing pool. Analysis of the latter pool by anion exchange chromatography revealed three KIF species: kinesin I (KIF5), kinesin II (KIF3), and KIF1C (Unc104/KIF1). The most abundant species, kinesin I, exhibited the expected long range microtubule gliding activity. By contrast, KIF1C did not move microtubules. Kinesin II, the second most abundant KIF, could be fractionated into two pools, one containing predominantly A/B isoforms and the other containing A/C isoforms. The two motor species had similar activities, powering microtubule gliding at slower speeds and over shorter distances than kinesin I.

Analysis of the roles of kinesin and dynein motors in microtubule-based transport in the Caenorhabditis elegans nervous system

The heteromeric kinesins constitute a subfamily of kinesin-related motor complexes that function in several distinct intracellular transport events. The founding member of this subfamily, heterotrimeric kinesin II, has been purified and characterized from early sea urchin embryos, where it was shown using antibody perturbation to be required for the synthesis of motile cilia, presumably by driving the anterograde transport of raft complexes. To further characterize heteromeric kinesin transport pathways, and to attempt to identify cargo molecules, we are using the model organism Caenorhabditis elegans to exploit its well-characterized nervous system and simple genetics. Here we describe methods for large-scale nematode growth and partial purification of kinesin-related holoenzymes from C. elegans, and an in vivo transport assay that allows the direct labeling and visualization of motor complexes and putative cargo molecules moving in living C. elegans neurons. This transport assay is being used to characterize the in vivo transport properties of motor enzymes in living cells, and to exploit a number of existing mutations in C. elegans that may represent constituents of heteromeric kinesin-driven transport pathways, for example, the retrograde intraflagellar transport motor CHE-3 dynein, as well as cargo molecules and/or regulatory molecules.

The bipolar kinesin, KLP61F, cross-links microtubules within interpolar microtubule bundles of Drosophila embryonic mitotic spindles

Previous genetic and biochemical studies have led to the hypothesis that the essential mitotic bipolar kinesin, KLP61F, cross-links and slides microtubules (MTs) during spindle assembly and function. Here, we have tested this hypothesis by immunofluorescence and immunoelectron microscopy (immunoEM). We show that Drosophila embryonic spindles at metaphase and anaphase contain abundant bundles of MTs running between the spindle poles. These interpolar MT bundles are parallel near the poles and antiparallel in the midzone. We have observed that KLP61F motors, phosphorylated at a cdk1/cyclin B consensus domain within the BimC box (BCB), localize along the length of these interpolar MT bundles, being concentrated in the midzone region. Nonphosphorylated KLP61F motors, in contrast, are excluded from the spindle and display a cytoplasmic localization. Immunoelectron microscopy further suggested that phospho-KLP61F motors form cross-links between MTs within interpolar MT bundles. These bipolar KLP61F MT-MT cross-links should be capable of organizing parallel MTs into bundles within half spindles and sliding antiparallel MTs apart in the spindle midzone. Thus we propose that bipolar kinesin motors and MTs interact by a "sliding filament mechanism" during the formation and function of the mitotic spindle.