Project Title

Microbial Voltage-gated Ion Channels

Presenters

Academic department under which the project should be listed

CSM - Molecular and Cellular Biology

Faculty Sponsor Name

Tsai-Tien Tseng

Abstract (300 words maximum)

Voltage-gated ion channels (VIC) form a superfamily that is well known for transporting potassium, sodium and calcium ions in excitable tissues. Ancestral members of this superfamily were thought to transport only potassium ions, unlike modern homologs from eukaryotes, which also transport sodium and calcium ions. The discovery of a sodium channel from Bacillus halodurans had significantly renewed the interest of physiological roles for ion transport in bacterial and archaeal species. Structurally, these bacterial channels shared the same topology with their eukaryotic counterparts while their shared history of evolution remained unresolved. The selectivity filter for ion specificity had a markedly different sequence composition that contradicted the canonical understanding of sodium-selectivity development, despite a highly conserved topology. This study addresses the inclusion of novel homologs into the overall evolution of ion-selectivity. An exhaustive similarity search was conducted on all domains of life to include all sequences that showed similarity to functionally characterized voltage-gated ion channels. Bacterial sequences were compared against other characterized sequences with multiple alignment to confirm the observed similarity to eukaryotic calcium selectivity pores. Phylogenetic trees were also built from these alignments to show that potassium-selective channels from ancestral bacteria gave rise to a potential calcium-selective precursor in addition to potential functional assignments of putative homologs. This precursor likely gave rise to sodium selectivity when passed to bacteria and calcium selectivity in eukaryotes. These findings would suggest that sodium specificity arose at least twice in VIC evolution, which provided the explanation for a sodium-selective channel from Bacillus halodurans.

Project Type

Poster

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Microbial Voltage-gated Ion Channels

Voltage-gated ion channels (VIC) form a superfamily that is well known for transporting potassium, sodium and calcium ions in excitable tissues. Ancestral members of this superfamily were thought to transport only potassium ions, unlike modern homologs from eukaryotes, which also transport sodium and calcium ions. The discovery of a sodium channel from Bacillus halodurans had significantly renewed the interest of physiological roles for ion transport in bacterial and archaeal species. Structurally, these bacterial channels shared the same topology with their eukaryotic counterparts while their shared history of evolution remained unresolved. The selectivity filter for ion specificity had a markedly different sequence composition that contradicted the canonical understanding of sodium-selectivity development, despite a highly conserved topology. This study addresses the inclusion of novel homologs into the overall evolution of ion-selectivity. An exhaustive similarity search was conducted on all domains of life to include all sequences that showed similarity to functionally characterized voltage-gated ion channels. Bacterial sequences were compared against other characterized sequences with multiple alignment to confirm the observed similarity to eukaryotic calcium selectivity pores. Phylogenetic trees were also built from these alignments to show that potassium-selective channels from ancestral bacteria gave rise to a potential calcium-selective precursor in addition to potential functional assignments of putative homologs. This precursor likely gave rise to sodium selectivity when passed to bacteria and calcium selectivity in eukaryotes. These findings would suggest that sodium specificity arose at least twice in VIC evolution, which provided the explanation for a sodium-selective channel from Bacillus halodurans.