Orthorhombic crystal structure of an insulin mutant B9Asp at 0.20 nm resolution

Human B9(Ser→Asp) insulin, a fast-absorption insulin analogue, was obtained by site-directed mutagenesis at B9 position. The orthorhombic crystal structure of B9Asp insulin was analyzed by crystallography at 0.20 nm resolution. Although no significant change of its overall conformation was observed, the local conformation flanking B9 site differed greatly from native T6 human insulin. The substitution of serine at B9 position by aspartic acid resulted in obvious alteration of local hydrophobic and hydrophilic interactions. As a result, the insulin dimer became unstable and the capability of the hexamer formation was diminished extensively. All these properties contribute to the fast-absorption of B9Asp. In addition, the open state of N-terminus of B-chain, which differs from T- or R- state, might suggest a new conformational state in the monomer or dimer insulin.