Purification, crystallization and preliminary crystallographic studies of a two fibronectin type-III domain segment from chicken tenascin encompassing the heparin- and contactin-binding regions

A fragment of chicken tenascin consisting of fibronectin type-III domains 5 and 6 has been expressed in Escherichia coli. After modifying a previously reported purification protocol, an electrophoretically homogeneous recombinant protein was obtained from which various crystal forms could be grown under identical conditions. Only one form was suitable for structure determination. These crystals belong to space group P2₁, with unit-cell parameters a = 45.2, b = 57.9, c = 72.2 Å, β = 91.4°, and diffract to at least 2.6 Å resolution using synchrotron radiation. From density measurements of the crystals, it was found that there are two molecules in the asymmetric unit. Diffraction data of native, two platinum-derivative and one palladium-derivative crystals were collected.