Axoneme beta-tubulin sequence determines attachment of outer dynein arms.
Axonemes of motile eukaryotic cilia and flagella have a conserved structure of nine doublet microtubules surrounding a central pair of microtubules. Outer and inner dynein arms on the doublets mediate axoneme motility [1]. Outer dynein arms (ODAs) attach to the doublets at specific interfaces [2-5]. However, the molecular contacts of ODA-associated proteins with tubulins of the doublet microtubules are not known. We report here that attachment of ODAs requires glycine 56 in the beta-tubulin internal variable region (IVR). We show that in Drosophila spermatogenesis, a single amino acid change at this position results in sperm axonemes markedly deficient in ODAs. Moreover, we found that axonemal beta-tubulins throughout the phylogeny have invariant glycine 56 and a strongly conserved IVR, whereas nonaxonemal beta-tubulins vary widely in IVR sequences. Our data reveal a deeply conserved physical requirement for assembly of the macromolecular architecture of the motile axoneme. Amino acid 56 projects into the microtubule lumen [6]. Imaging studies of axonemes indicate that several proteins may interact with the doublet-microtubule lumen [3, 4, 7, 8]. This region of beta-tubulin may determine the conformation necessary for correct attachment of ODAs, or there may be sequence-specific interaction between beta-tubulin and a protein involved in ODA attachment or stabilization.
Raff
Elizabeth C
EC
Department of Biology, Indiana Molecular Biology Institute, Indiana University, Bloomington, IN 47405, USA. raff@indiana.edu <raff@indiana.edu>
Hoyle
Henry D
HD
Popodi
Ellen M
EM
Turner
F Rudolf
FR
D000595:Amino Acid Sequence; D000818:Animals; D054468:Axoneme / Q000378:metabolism / Q000648:ultrastructure*; D004330:Drosophila / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D004398:Dyneins / Q000378:metabolism*; D005998:Glycine / Q000737:chemistry; D008297:Male; D008969:Molecular Sequence Data; D011487:Protein Conformation; D013091:Spermatogenesis / Q000502:physiology*; D013094:Spermatozoa / Q000378:metabolism / Q000648:ultrastructure; D014057:Tomography, X-Ray Computed; D014404:Tubulin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D014404:Tubulin; D004398:Dyneins; D005998:Glycine