I am looking for PDB file for Osteopontin (SPP1). The entry- 3CXD shows the structure of an Osteopontin antibody, not of the protein itself. Thanks
There doesn't seem to be a 3D structure of Osteopontin available, and after looking a bit at the literature about this protein I'm not really surprised.
Osteopontin is hypothesized to assume an elongated and flexible structure (Sodek et al., 2000). Flexible proteins are very hard to impossible to crystallize, typically the flexible parts are either removed or stabilized in some way. I'm not a crystallographer, but this protein doesn't look like it can be crystallized in the full form.
For NMR it is a bit on the large side, a full structure would likely be not feasible.
It also has extensive posttranslational modifications, which makes it much harder to produce in large amounts as needed for crystallography, and extremely expensive for NMR where you would have to isotope-label the protein as well.
only a small peptide of Osteopontin is available currently