Towards the molecular mechanism of Na(+)/solute symport in prokaryotes

Biochim Biophys Acta. 2001 May 1;1505(1):131-43. doi: 10.1016/s0005-2728(00)00283-8.


The Na(+)/solute symporter family (SSF, TC No. 2.A.21) contains more than 40 members of pro- and eukaryotic origin. Besides their sequence similarity, the transporters share the capability to utilize the free energy stored in electrochemical Na(+) gradients for the accumulation of solutes. As part of catabolic pathways most of the transporters are most probably involved in the acquisition of nutrients. Some transporters play a role in osmoadaptation. With a high resolution structure still missing, a combination of genetic, protein chemical and spectroscopic methods has been used to gain new insights into the structure and molecular mechanism of action of the transport proteins. The studies suggest a common 13-helix motif for all members of the SSF according to which the N-terminus is located in the periplasm and the C-terminus is directed into the cytoplasm (except for proteins containing a N- or C-terminal extension). Furthermore, an amino acid substitution analysis of the Na(+)/proline transporter (PutP) of Escherichia coli, a member of the SSF, has identified regions of particular functional importance. For example, amino acids of TM II of PutP proved to be critical for high affinity binding of Na(+) and proline. In addition, it was shown that ligand binding induces widespread conformational alterations in the transport protein. Taken together, the studies substantiate the common idea that Na(+)/solute symport is the result of a series of ligand-induced structural changes.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Transport Systems, Neutral*
  • Bacterial Proteins / metabolism*
  • Binding Sites
  • Carrier Proteins / chemistry
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Cations, Monovalent
  • Cytoplasm / metabolism
  • Escherichia coli / metabolism
  • Escherichia coli Proteins*
  • Ligands
  • Models, Chemical
  • Molecular Sequence Data
  • Periplasm / metabolism
  • Proline / metabolism
  • Protein Conformation
  • Sodium / metabolism*
  • Symporters*


  • Amino Acid Transport Systems, Neutral
  • Bacterial Proteins
  • Carrier Proteins
  • Cations, Monovalent
  • Escherichia coli Proteins
  • Ligands
  • Symporters
  • PutP protein, E coli
  • Proline
  • Sodium