Cytoplasmic Dynein

Cytoplasmic dynein is a rather large multi-subunit protein complex composed of two identical heavy chains of about 530 kDa each (dark blue), two 74 kDa intermediate chains (magenta and yellow) and about four 53-59 kDa intermediate chains (green). In addition, there are several light chains that we know less about. The heavy chains each contain four ATP-binding sites, including the ATP-hydrolytic site that provides the energy for its movement along microtubules, and a microtubule binding site.

The 74 kDa intermediate chains are thought to bind the dynein to its cargo, whether that cargo is a membrane-bounded vesicle in a neuron, a golgi vesicle, a kinetochore or a mitotic spindle astral microtubule. The dynein then provides the force to move this cargo along a microtubule toward its minus end.

We have recently been concentrating on the 74 kDa intermediate chain (hereinafter refered to as IC74). When we run 2D gels of dynein immuno-precipitated from adult rat brain, we see six IC74 spots:

Work from Kevin Vaughn in Richard Vallee's lab has shown that the IC74's are actually encoded by two genes, one of which has two alternative splice variants and the other has three splice variants. In addition, we have shown that most of these spots are phosphorylated. Using an RT-PCR analysis of various tissues, some of which express only subsets of these IC74 variants, in combination with phosphatase treatment of immuno-precipitated IC74, we can now account for all of these spots.

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