National Institute for Basic Biology

Radioisotope Facility

(Managed by NIBB)

Takashi Horiuchi
Associate Professor:
Kazuo Ogawa
NIBB Postdoctoral Fellow:
Hiroyuki Takai
Technical Staffs:
Kazuhiko Furukawa (Radiation Protection Supervisor)
Yosuke Kato (Radiation Protection Supervisor)
Yoshimi Matsuda (Radiation Protection Supervisor)

This Facility consists of a main center and two branch offices. The third branch office will open in the laboratory of Gene Expression and Regulation in May 1, 1977. The members of the Radioisotope Facility are engaged in maintaining and controlling both the center and two branch offices, and providing users an appropriate guidance for radioisotope handling.

The teaching staffs are also engaged in their own research. They are interested in clarifying the structure and function of dynein motor protein. Dyneins are a group of microtubule-activated ATPases that serve to convert chemical energy into mechanical energy. They have been divided into two large subgroups, namely, the axonemal and cytoplasmic dyneins. Figure 1 shows the localization of two dyneins in the outer arms (Ogawa et al., 1977) and the mitotic apparatus (Mohri et al., 1976) that have been visualized by the same antibodies directed against the motor domain of axonemal dynein (fragment A).

Figure 1.
Localization of dynein in sea urchin sperm axoneme (A) and a cleaving egg (B).

The native dyneins are very large. They range in molecular mass up to 1 to 2 mega daltons and they are complex proteins as shown in Figure 2. Each dynein contains two or three heavy chains (HCs) with ATPase activity, which range in molecular mass up to 500 kDa. The motor activity of dynein is associated with these chains. Some functional differences have been reported between HCs of outer arm dynein. Sea urchin outer arm dynein is a heterodimer of HCs (alpha and beta) and at least the beta-HC is able to induce gliding of microtubules in vitro. The Alpha-HC might amplify the function of beta-HC and it has been reported to have no motile activity. After the first cloning of beta-HC from sea urchin ciliary axonemes (Gibbons et al., 1991; Ogawa, 1991), the sequences of HCs of axonemal and cytoplasmic dyneins from a variety of organisms were determined in their entirety. Without exception, all the HCs cloned to date contain four P-loop (ATP-binding) sequences in the midregion of the molecule. Thus, they can be classified as a four P-loop family.

Figure 2.
Substructures of outer arm dyneins from sea urchin sperm flagella and Chlamydomonas flagella.

The outer arm dyneins contain two or three proteins that range in molecular mass from 70 to 120 kDa and copurify with HCs. ICs of sea urchin outer-arm dynein are abbreviated as IC1, IC2, and IC3. Those of Chlamydomonas are called IC78 and IC69, and ICs of cytoplasmic dynein are called IC74. Chlamydomonas IC78 and IC69 were cloned by Wilkerson et al. (1995) and Mitchell and Kang (1991), respectively. The sequences of sea urchin IC2 and IC3 were determined by Ogawa et al. (1995). Finally, the sequence of IC1 was determined this year by Ogawa et al. (1996). Thus, all the ICs found in the axonemal and cytoplasmic dyneins of the model organisms used for studies of dynein function have been completely sequenced. Comparison of amino acid sequences of IC2 and IC3 with those of IC78 and IC69 and with that of IC74 showed that, although all five ICs are homologous, IC2 is much more closely related to IC78, and IC3 is much more closely related to IC69, than either sea urchin chain or either Chlamydomonas chain is related to each other. Regions of similarity between all five ICs are limited to the carboxy-terminal halves of the molecules. Similarity are due primarily to conservation of the WD repeats in all of these chains. The WD repeats are involved in protein-protein interactions in a large family of regulatory molecules (Neer et al.,1994). A parsimony tree for these chains (Ogawa et al., 1995) shows that, although the carboxy-terminal halves of all of these chains contain WD repeats, the chains can be divided into three distinct subclasses (IC3 plus IC69, IC2 plus IC78, and IC78).

By contrast, sea urchin IC1 is not a member of the WD family. IC1 has a unique primary structure, the N-terminal part is homologous to the sequence of thioredoxin, the middle part consists of three repetitive sequences homologous to the sequence of nucleoside diphosphate kinase, and the C-terminal part contains a high proportion of negatively charged glutamic acid residues. Thus, IC1 is a novel dynein intermediate chain distinct from IC2 and IC3 and may be a multifunctional protein. Then, a question arises as whether Chlamydomonas outer arm dynein contains IC1. The answer is "no". Because it consists of just two intermediate chains. Alternatively, the answer is "yes". Because the sequences of two light chains (LC16 and LC14) from Chlamydomonas outer arm dynein shows that they are members of novel family of thioredoxin (Patel-King et al. 1996). The thioredoxin-related part of IC1 is more closely related to those of two redox-active Chlamydomonas light chains than thioredoxin. Antibodies were prepared against the N-terminal and middle domains of IC1 expressed as His-tagged proteins in bacteria. These antibodies cross-reacted with some dynein polypeptides (potential homologues of IC1) from distantly related species. We propose here that the three intermediate chains are the basic core units of sperm outer arm dynein because of their ubiquitous existence.

Publication List:
Kazuo Ogawa, Hiroyuki Takai, Atsushi Ogiwara, Etsuo Yokota, Takashi Shimizu, Kazuo Inaba, and Hideo Mohri (1996) Is outer arm dynein intermediate chain 1 multifunctional? Mol. Biol. Cell 7, 1895-1907.
Kazuo Ogawa and Hideo Mohri (1996) A dynein motor superfamily. Cell Struct. Funct. 21, 343-349.
Last Modified: 12:00, June 27, 1997