A novel rare splice variant of the human voltage‐dependent proton channel hH V 1

Diversity among human voltage‐gated proton channels (hH V 1) arises exclusively from alternative splicing or post‐translational modification. In addition to the canonical 273‐amino acid form (hH V 1‐l), two shorter isoforms, HVCN1 S and H V 1Sper, have been described, both characterized by truncated N‐terminal domains. To date, isoforms longer than hH V 1‐l were unidentified in humans. Here, we report a novel ‘very‐long’ hH V 1 splice variant (hH V 1‐vl) containing a 47 amino acid N‐terminal insertion derived from alternative splicing of exon 12 of the HVCN1 gene . The additional amino acid sequence is predicted to be largely unstructured and contains several potential phosphorylation sites. Molecular dynamics simulations further suggest that the conserved poly‐glutamate motif downstream of Thr29 can interact with cytosolic arginine residues at the base of the S4 segment. Nested PCR unambiguously identified hH V 1‐vl in healthy tissues (pons and choroid plexus epithelial cells) as well as in three different types of lymphoma. However, quantitative PCR showed that hH V 1‐vl is expressed at low levels in the analyzed tissues, 0.3–2% of the total HVCN1 transcripts. Heterologous expression of hH V 1‐vl followed by patch‐clamp recordings demonstrated that this isoform retains the key properties of proton channels, including high proton selectivity and voltage‐ and pH‐dependent conductance. Compared with the canonical 273‐amino acid hH V 1‐l isoform, hH V 1‐vl exhibits similar gating parameters, including proton selectivity, ΔpH‐dependent gating, conductance density, g H – V relationship, and closing kinetics, but shows markedly slower activation kinetics.