Crystallographic studies of insulin crystals grown in microgravity

Data have been measured from T3R3 insulin crystals, grown in microgravity and complexed with p‐hydroxybenzamide, to a resolution of 1.4 A. The X‐ray diffraction data which have been measured from these crystals are superior in every respect to those grown in normal gravity and the resulting electron density maps demonstrate considerably more detail than earlier maps. During the refinement of the structure, the primary p‐hydroxybenzamide molecule was found to bind in the expected position through the formation of a pair of hydrogen bonds to A6 Cys and A11 Cys. As the refinement progressed, a second p‐hydroxybenzamide molecule was identified deeper within the phenolic binding site where it participates in an extensive hydrogen bonded network extending from the surface of the hexamer to the interior. This was an unexpected result and is the first time that an R‐state trimer has been found to bind six molecules of a phenolic derivative.