Structural analysis of desheptapeptide (B24-B30) insulin by molecular replacement

Desheptapeptide (B24-B30) insulin (DHPI), a virtually inactive insulin analog, has been crystallized in space group P2(1)2(1)2(1) with two DHPI molecules in an asymmetric unit. The orientations and positions of the molecules were determined by molecular replacement, and a structural model was built at 0.3 nm resolution. The current model shows that the two DHPI monomers are related by a non-crystallographic 2-fold axis, nearly parallel to the crystallographic c axis. This structural feature complicated the determination of the orientation of the local 2-fold axis, which was later confirmed by analysing the diffraction data of DHPI crystals.