PMID:9693722
| Citation |
Jung, H (1998) Topology and function of the Na+/proline transporter of Escherichia coli, a member of the Na+/solute cotransporter family. Biochim. Biophys. Acta 1365:60-4 |
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| Abstract |
The Na+/proline transporter of Escherichia coli (PutP) is a member of the Na+/solute contransporter family (SCF) and catalyzes the uptake of proline by a Na+ dependent transport mechanism. Hydropathy profile analysis suggests that the protein consists of 12 transmembrane domains (TMs) that traverse the membrane in zigzag fashion connected by hydrophilic loops. However, analysis of a series of putP-phoA (PutP-alkaline phosphatase) and putP-lacZ (PutP-beta-galactosidase) fusions and site-directed labeling of the transporter indicate a 13-helix motif with the N-terminus on the outside and the C-terminus facing the cytoplasm. The findings are discussed with respect to a common topological motif for all members of the SCF. Furthermore, amino acid substitution analysis indicates that the N-terminal part of PutP is important for ion binding. Thus, Asp55 (putative TM II) is essential for transport and proposed to interact directly with Na+. The functional importance of TM II is further confirmed by the observation that replacement of Arg40, Ser50, Ala53, or Ser57 alters transport kinetics dramatically. |
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| Keywords |
Amino Acid Sequence; Amino Acid Transport Systems, Neutral; Carrier Proteins/chemistry; Carrier Proteins/genetics; Carrier Proteins/physiology; Escherichia coli/metabolism; Escherichia coli Proteins; Membrane Transport Proteins/chemistry; Membrane Transport Proteins/genetics; Membrane Transport Proteins/physiology; Membranes/metabolism; Molecular Sequence Data; Mutagenesis, Site-Directed; Proline; Protein Structure, Secondary; Sodium; Structure-Activity Relationship; Symporters |
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