A novel neuronal calcium sensor family protein, calaxin, is a potential Ca(2+)-dependent regulator for the outer arm dynein of metazoan cilia and flagella.
BACKGROUND
Spermatozoa show several changes in flagellar waveform, such as upon fertilization. Ca(2+) has been shown to play critical roles in modulating the waveforms of sperm flagella. However, a Ca(2+)-binding protein in sperm flagella that regulates axonemal dyneins has not been fully characterized.


RESULTS
We identified a novel neuronal calcium sensor family protein, named calaxin (Ca(2+)-binding axonemal protein), in sperm flagella of the ascidian Ciona intestinalis. Calaxin has three EF-hand Ca(2+)-binding motifs, and its orthologues are present in metazoan species, but not in yeast, green algae or plant. Immunolocalization revealed that calaxin is localized near the outer arm of the sperm flagellar axonemes. Moreover, it is distributed in adult tissues bearing epithelial cilia. An in vitro binding experiment indicated that calaxin binds to outer arm dynein. A cross-linking experiment showed that calaxin binds to beta-tubulin in situ. Overlay experiments further indicated that calaxin binds the beta-dynein heavy chain of outer arm dynein in the presence of Ca(2+).


CONCLUSIONS
These results suggest that calaxin is a potential Ca(2+)-dependent modulator of outer arm dynein in metazoan cilia and flagella.
Mizuno
Katsutoshi
K
Shimoda Marine Research Center, University of Tsukuba, Shimoda, Shizuoka, Japan.
Padma
Potturi
P
Konno
Aru
A
Satouh
Yuhkoh
Y
Ogawa
Kazuo
K
Inaba
Kazuo
K
D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D002696:Chlamydomonas / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D002923:Cilia / Q000235:genetics / Q000378:metabolism*; D004398:Dyneins / Q000235:genetics / Q000378:metabolism*; D005407:Flagella / Q000235:genetics / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D005810:Multigene Family; D051580:Neuronal Calcium-Sensor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D011485:Protein Binding; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013094:Spermatozoa / Q000737:chemistry / Q000378:metabolism*
D051580:Neuronal Calcium-Sensor Proteins; D015800:Protozoan Proteins; D004398:Dyneins; D002118:Calcium