Topology and function of the Na+/proline transporter of Escherichia coli, a member of the Na+/solute cotransporter family.
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.
Universität Osnabrück, Fachbereich Biologie/Chemie, Osnabrück, Germany. Jung_H@mail.biologie.uni-osnabrueck.de
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D000595:Amino Acid Sequence; D026921:Amino Acid Transport Systems, Neutral; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008566:Membranes / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011392:Proline; D017433:Protein Structure, Secondary; D012964:Sodium; D013329:Structure-Activity Relationship; D027981:Symporters
D026921:Amino Acid Transport Systems, Neutral; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D027981:Symporters; C060609:PutP protein, E coli; C033082:proline transporter; D011392:Proline; D012964:Sodium