Lysine exporter


Lysine Exporters are a superfamily of transmembrane proteins which export amino acids, lipids and heavy metal ions. They provide ionic homeostasis, play a role in cell envelope assembly, and protect from excessive concentrations of heavy metals in cytoplasm. The superfamily was named based on the early discovery of the LysE carrier protein of Corynebacterium glutamicum.

Families

- The L-Lysine Exporter Family
- The Resistance to Homoserine/Threonine Family
- The Cadmium Resistance Family
- The 6TMS Neutral Amino Acid Transporter Family
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- The Mn2+ exporter Family
- The Iron/Lead Transporter Family
- The Tellurium Ion Resistance Family
- The Nickel/Cobalt Transporter Family
- The Peptidoglycolipid Addressing Protein Family
- The Disulfide Bond Oxidoreductase D Family

The LysE family

Two members of the LysE family have been functionally characterized, but functionally uncharacterized homologues are encoded within the genomes of many bacteria including Bacillus subtilis, Mycobacterium tuberculosis, Aeromonas salmonicida, Helicobacter pylori, Vibrio cholerae and Yersinia pestis. Thus, LysE family members are found widely distributed in Gram-negative and Gram-positive bacteria.

Structure

These proteins are 190-240 amino acyl residues in length and possess six hydrophobic regions. PhoA fusion analyses of LysE of C. glutamicum provided evidence for a 5 transmembrane α-helical spanner typology with the N-terminus inside and the C-terminus outside. However, some evidence suggests a 6 TMS topology.

Function

LysE appears to catalyze unidirectional efflux of L-lysine, and it provides the sole route for L-lysine excretion. The energy source is believed to be the proton motive force. The E. coli ArgO homologue effluxes arginine and possibly lysine and canavanine as well.
Early studies showed that the LysE family is related to the RhtB family as well as the CadD family based both on the similar sizes and topologies of their members and on PSI-BLAST results.

Generalized Transport Reaction

The generalized transport reaction for LysE is:
Lysine + Lysine + .