title: Structural insight into the PTS sugar transporter EIIC.
abstract: BACKGROUND
  The enzyme IIC (EIIC) component of the phosphotransferase system (PTS) is responsible for selectively transporting sugar molecules across the inner bacterial membrane. This is accomplished in parallel with phosphorylation of the sugar, which prevents efflux of the sugar back across the membrane. This process is a key part of an extensive signaling network that allows bacteria to efficiently utilize preferred carbohydrate sources.
  
  
  METHODS
  The goal of this review is to examine the current understanding of the structural features of the EIIC and how it mediates concentrative, selective sugar transport. The crystal structure of an N,N'-diacetylchitobiose transporter is used as a structural template for the glucose superfamily of PTS transporters.
  
  
  CONCLUSIONS
  Comparison of protein sequences in context with the known EIIC structure suggests that members of the glucose superfamily of PTS transporters may exhibit variations in topology. Despite these differences, a conserved histidine and glutamate appear to have roles shared across the superfamily in sugar binding and phosphorylation. In the proposed transport model, a rigid body motion between two structural domains and movement of an intracellular loop provide the substrate binding site with alternating access, and reveal a surface required for interaction with the phosphotransfer protein responsible for catalysis.
  
  
  CONCLUSIONS
  The structural and functional data discussed here give a preliminary understanding of how transport in EIIC is achieved. However, given the great sequence diversity between varying glucose-superfamily PTS transporters and lack of data on conformational changes needed for transport, additional structures of other members and conformations are still required. This article is part of a Special Issue entitled: Structural biochemistry and biophysics of membrane proteins.
authors.affiliation: Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: Jason G
authors.initials: JG
authors.lastname: McCoy
authors.affiliation: Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: Elena J
authors.initials: EJ
authors.lastname: Levin
authors.affiliation: Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: Ming
authors.initials: M
authors.lastname: Zhou
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005947:Glucose / Q000737:chemistry* / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; C436306:ChbC protein, Borrelia burgdorferi; D026901:Membrane Transport Proteins; D005947:Glucose
keywords: ChbC; Enzyme IIC; Membrane protein; Phosphotransferase system; Sugar transport; Transporter