Conformational analysis of the leukocyte-specific EF-hand protein p65/L-plastin by X-ray scattering in solution

p65/L-Plastin is a leukocyte-specific EF-hand protein which plays a vital role in organizing the actin cytoskeleton. Since its overall structural information has been largely unknown, we employed the X-ray scattering technique to elucidate the structure. Kratky plots of p65/l-plastin showed one peak, indicating that the protein takes compact globular conformations. The radii of gyration (Rg) of the monomer p65/l-plastin estimated from Guinier plots were 27.5 ± 0.5 Å and 28.6 Å in the absence and presence of Ca2+, respectively. The distance distribution function P(r) gave single peaks at 31.5-32.3 Å and 33 Å in the absence and presence of Ca2+, respectively. These indicate that p65/l-plastin becomes somewhat larger in the presence of Ca2+. The molecular shape of p65/l-plastin reconstructed from X-ray scattering data using the DAMMIN program has provided the first view of the overall structure of full-length plastin/fimbrin family proteins: a compact horseshoe-like shape with a small projection, which also exhibits Ca2+-induced conformational changes.