An exchanger-like protein underlies the large Mg2+ current in Paramecium

AUTOR(ES)

Haynes, W. John

FONTE

National Academy of Sciences

RESUMO

There are very few molecules known to transport Mg2+ in eukaryotes. The membrane of Paramecium tetraurelia passes a large Mg2+-selective current and exhibits a corresponding backward swimming behavior. Both are missing in a group of mutants called eccentric. By sorting an indexed WT genomic library through microinjection into the macronucleus, we have isolated a DNA fragment that complements the eccentric mutations. The Mg2+ currents and behavior are restored fully in the transformed cells. Surprisingly, the conceptually translated protein is not homologous to any known ion channel but instead has some similarity to K+-dependent Na+/Ca2+ exchangers. Exchangers are either electrically silent or only pass very small and slow currents compared with ion-channel currents. In light of recent ion-channel crystal structures and considering the need to have narrow ion-selective filters, we speculate on how an exchanger might evolve to show channel-like activities in special circumstances. The significance of finding the molecular basis of a Mg2+-specific pathway is also discussed.

Documentos Relacionados

• Mg2+-dependent gating of bacterial MgtE channel underlies Mg2+ homeostasis
• Mechanisms of glutamate-stimulated Mg2+ influx and subsequent Mg2+ efflux in rat forebrain neurones in culture.
• The Mg2+ block and intrinsic gating underlying inward rectification of the K+ current in guinea-pig cardiac myocytes.
• An optimal Mg2+ concentration for kinetic folding of the Tetrahymena ribozyme
• Mrs2p is an essential component of the major electrophoretic Mg2+ influx system in mitochondria