title: Structure and function of SemiSWEET and SWEET sugar transporters.
abstract: SemiSWEETs and SWEETs have emerged as unique sugar transporters. First discovered in plants with the help of fluorescent biosensors, homologs exist in all kingdoms of life. Bacterial and plant homologs transport hexoses and sucrose, whereas animal SWEETs transport glucose. Prokaryotic SemiSWEETs are small and comprise a parallel homodimer of an approximately 100 amino acid-long triple helix bundle (THB). Duplicated THBs are fused to create eukaryotic SWEETs in a parallel orientation via an inversion linker helix, producing a similar configuration to that of SemiSWEET dimers. Structures of four SemiSWEETs have been resolved in three states: open outside, occluded, and open inside, indicating alternating access. As we discuss here, these atomic structures provide a basis for exploring the evolution of structure-function relations in this new class of transporters.
authors.affiliation: Department of Molecular and Cellular Physiology, 279 Campus Drive, Stanford University School of Medicine, Stanford, CA 94305, USA. Electronic address: liangf@stanford.edu.
authors.forename: Liang
authors.initials: L
authors.lastname: Feng
authors.affiliation: Carnegie Institution for Science, Department of Plant Biology, 260 Panama St, Stanford, CA 94305, USA. Electronic address: wfrommer@carnegiescience.edu.
authors.forename: Wolf B
authors.initials: WB
authors.lastname: Frommer
mesh_terms: D000818:Animals; D001692:Biological Transport; D006601:Hexoses / Q000378:metabolism*; D006801:Humans; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D011487:Protein Conformation
chemical_list: D006601:Hexoses; D026901:Membrane Transport Proteins
keywords: carrier; crystal structure; fructose; glucose; hexose; sucrose