Prostaglandin E2 synthase
Secondary transport of sugars and other solutes across membrane barriers is carried out by specific membrane proteins which seem to have either 6 or 12 transmembrane helices. In E. coli the translocation of melibiose is performed by melibiose permease (MelB). As a result of an EU project on secondary transporters we were able to make 2-D crystals of MelB. Two types of tubular 2-D crystals are observed. As they flatten on the support film during preparation two crystalline layers on top of each other are formed. The information from these can be separated during image processing. In a conventional electron microscope the crystals give information to 8 Å resolution. Our recently published projection structure at this resolution level resembles that of a Na-antiporter also analysed with electron crystallography.
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