Favourable mediation of crystal contacts by cocoamidopropylbetaine (CAPB).

Crystals of excellent quality are a prerequisite for high-resolution X-ray data. However, in refinement protocols of crystallization conditions it is often difficult to obtain the right combination of, for example, protein concentration, drop size, temperature and additives. A novel approach for optimizing crystal contacts in a most favourable fashion by performing crystallization setups with the zwitterionic surfactant cocoamidoproylbetaine (CAPB) is introduced. In the presence of this surfactant, highly diffracting crystals were obtained. Here, data from a right-handed coiled coil (RHCC) in complex with CAPB at 1.4 A resolution are presented. The addition of CAPB using otherwise identical crystallization conditions and the same X-ray source caused an improvement in resolution from 2.9 to 1.4 A.