Light chains of mammalian cytoplasmic dynein: Identification and characterization of a family of LC8 light chains

Cytoplasmic dynein is a large multisubunit motor protein that moves various cargoes toward the minus ends of microtubules. in addition to the previous ly identified heavy, intermediate, and light intermediate chains, it has re cently been recognized that cytoplasmic dynein also has several light chain subunits with apparent molecular weights between 8-20 kDa. To systematical ly identify the light chains of purified rat brain cytoplasmic dynein, pept ide sequences were obtained from each light chain band resolved by gel elec trophoresis. Both members of the tctex 1 light chain family, tctex 1 and rp 3, were identified in a single band. Only one member of the roadblock famil y, roadblock-2, was found. Two members of the LC8 family were resolved as s eparate bands, the previously identified LC8 subunit, and a second novel cy toplasmic dynein family member, LC8b. The tissue distribution of these two dynein LC8 subunits differed, although LC8b was the major family member in brain. Database searches found that both LC8a and LC8b were also present in several mammalian species, and a third mammalian LC8 sequence, LC8c was fo und in the human database. The amino acid sequences of both LC8a and LC8b w ere completely conserved in mammals. LC8a and LC8b differ in only six of th e 89 amino acids. The amino acid differences between LC8a and LC8b were loc ated near the N-terminus of the molecules, and most were in the outward fac ing alpha -helices of the LC8 dimer. When the mammalian LC8a sequence was c ompared to the LC8 sequences found in six other animal species including Xe nopus and Drosophila, there was, on average, 94% sequence identity. More va riation was found in LC8 sequences obtained from plants, fungi, and parasit es. LC8c differed from the other two human LC8 sequences in that it has ami no acid substitutions in the intermediate chain binding domain at the C-ter minal of the molecule. The position of amino acid substitutions of the thre e mammalian LC8 family members is consistent with the hypothesis that they bind to different proteins. Cell Motil. Cytoskeleton 49:229-240, 2001. (C) 2001 Wiley-Liss, Inc.