Format

Send to

Choose Destination
Biochim Biophys Acta. 2011 Feb;1807(2):167-88. doi: 10.1016/j.bbabio.2010.10.014. Epub 2010 Oct 26.

The structural basis of secondary active transport mechanisms.

Author information

1
Structural Biology Department, Max Planck Institute for Biophysics, Frankfurt, Germany.

Abstract

Secondary active transporters couple the free energy of the electrochemical potential of one solute to the transmembrane movement of another. As a basic mechanistic explanation for their transport function the model of alternating access was put forward more than 40 years ago, and has been supported by numerous kinetic, biochemical and biophysical studies. According to this model, the transporter exposes its substrate binding site(s) to one side of the membrane or the other during transport catalysis, requiring a substantial conformational change of the carrier protein. In the light of recent structural data for a number of secondary transport proteins, we analyze the model of alternating access in more detail, and correlate it with specific structural and chemical properties of the transporters, such as their assignment to different functional states in the catalytic cycle of the respective transporter, the definition of substrate binding sites, the type of movement of the central part of the carrier harboring the substrate binding site, as well as the impact of symmetry on fold-specific conformational changes. Besides mediating the transmembrane movement of solutes, the mechanism of secondary carriers inherently involves a mechanistic coupling of substrate flux to the electrochemical potential of co-substrate ions or solutes. Mainly because of limitations in resolution of available transporter structures, this important aspect of secondary transport cannot yet be substantiated by structural data to the same extent as the conformational change aspect. We summarize the concepts of coupling in secondary transport and discuss them in the context of the available evidence for ion binding to specific sites and the impact of the ions on the conformational state of the carrier protein, which together lead to mechanistic models for coupling.

PMID:
21029721
DOI:
10.1016/j.bbabio.2010.10.014
[Indexed for MEDLINE]
Free full text

Supplemental Content

Full text links

Icon for Elsevier Science
Loading ...
Support Center