Structure of desheptapeptide (B24-B30) insulin in a new crystal form

The structure of desheptapeptide (B24-B30) insulin (DHPI) in a new crystal form (form B) has been determined and refined to 0.2 nm resolution. The cry stals were obtained under the same crystallization condition as previously reported crystal form (form A). The overall structures of the two crystal f orms are similar but obvious differences can be observed in crystal packing and local conformation. The crystal structures of the two forms show that the two independent molecules in an asymmetric unit from a DHPI dimer, and the dimer formation buries mole than 18.20 and 16.95 nm(2) of solvent acces sible surfaces for form A and form B DHPI, respectively, the largest among insulin and insulin analogs ever reported. Close examination at crystal pac king shows that the dimer-forming surface of DHPI, namely Surface II, is no rmally present in the association of insulin and insulin analogs in their c rystal structures. The results demonstrate that Surface II is crucially imp ortant for the formation of two crystal forms under the same crystallizatio n condition.