We are systematically embarking on experiments to improve the quality ofcrystals of human aquaporin-1 (AQP-1). To date, the best crystals diffract (at a synchrotron) to approximately 4A resolution, with a few very weak spots to approximately 3.5A resolution. For integral membrane proteins, the detergent that is used during crystallization can have a profound effect upon crystal quality (or even the existnece or lack of existence of crystals). Therefore, exchange into various detergents and subsequent crystallization is underway. We have a major effort to develop membrane protein crystallization screens. Modification of the protein by glycosidases or proteases is also underway. It is imperative to have access to synchrotrons in order to be able to examine the crystals that are obtained from crystallization screens, as well as to collect data from better-quality crystals. Historically, membrane protein crystals have been of poorer quality than soluble protein crystals, necessitating the frequent use of synchrotrons. Aquaporin-1 is the subject of study by electron crystallographic methods, whcih has yielded a variety of lower-resolution structural information. We are using models based upon these results to carry out molecular replacement structure determation at low resolution. Such a low-resolution structure would be a useful intermediate result.
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