ZnT5b

ZnT5b is an isoform of the zinc transporter ZnT5, encoded by the human SLC30A5 gene. It arises from an alternative promoter that yields an N-terminally distinct transcript, ZnT5b, in contrast to the ZnT5a isoform. Like other ZnT family members, ZnT5b contributes to cellular zinc homeostasis by moving zinc into intracellular compartments.

ZnT transporters in the SLC30 family generally import zinc from the cytosol into organelles or out of the cytosol. ZnT5b shares the conserved transport domain with ZnT5a but differs at the N-terminus due to alternative transcription, which can influence localization and regulation of the protein.

Localization studies indicate ZnT5b resides in intracellular compartments involved in zinc handling, with evidence for localization to Golgi-associated membranes and/or late endosomes/lysosome-related organelles in a cell-type dependent manner. This contrasts with ZnT5a, which is commonly associated with the Golgi apparatus, highlighting potential isoform-specific roles within secretory pathway compartments.

Functionally, ZnT5b is believed to mediate zinc import into the lumen of secretory pathway organelles, contributing to zinc sequestration in the Golgi and related compartments and providing zinc for zinc-dependent enzymes and processes within the secretory pathway. The precise substrates and regulatory mechanisms of ZnT5b are areas of ongoing research.

Research into ZnT5b's physiological role remains active. Although less studied than ZnT5a, ZnT5b is thought to work alongside other ZnT5 isoforms to support cellular zinc homeostasis, with potential implications for tissues relying on secretory pathway zinc handling and enzyme maturation.

See also: SLC30A5, ZnT family, zinc transporter.