The use of protein templates to direct the formation of inorganic nanostructures offers a novel bio-inspired route to nanomaterial synthesis that avoids the use of harsh reaction conditions and offers unique functionalities including biocompatibility and hierarchical assembly. Pair distribution function (PDF) analysis from total X-ray scattering has been used to determine the structure of TiO2 nanoparticles grown within an icosahedral virus capsid. The protein-TiO2 composites are similar to nanocrystalline anatase and show photocatalytic activity. PDF analysis is ideally suited to the study of protein-inorganic nanocomposites, and may be able to provide information about the hard/soft interface.