Outer dense fibre protein 2 (ODF2) is a self-interacting centrosomal protein with affinity for microtubules

Outer dense fibre protein 2 (ODF2) is a major protein of sperm tail outer dense fibres which are prominent sperm tail-specific cytoskeletal structures. Moreover, ODF2 was also identified as a widespread component of the centrosomal scaffold and was found to associate preferentially with the appendages of the mother centriole [Nakagawa, Y., Yamane, Y., Okanoue, T., Tsukita, S. and Tsukita, S. (2001) Mol. Biol. Cell 12, 1687-1697]. Secondary structure predictions indicated ODF2 as an overall coiled-coil protein with a putative fibre forming capacity. To investigate its potential functions in generating the centrosomal scaffold and in microtubule nucleation we asked whether ODF2 is able to form a fibrillar structure by self-association in vivo and if it interacts with microtubules. By cytological investigation of transfected mammalian cells expressing ODF2-GFP fusion proteins and in vitro coprecipitation assays we could demonstrate that ODF2 is a self-interacting protein that forms a fibrillar structure partially linked to the microtubule network. Microtubule cosedimentation and coprecipitation assays indicated ODF2 as a microtubule-associated protein. However, we could not demonstrate a direct interaction of ODF2 with tubulin, suggesting that binding of endogenous ODF2 to the axonemal as well as to centrosomal microtubules may be mediated by, as yet, unknown proteins.