Human TMEM16K (ANO10); A Target Enabling Package

There are ten members of the TMEM16/Anoctamin family of proteins in mammals. Although the first members of this family to be discovered, TMEM16A and TMEM16B, have a calcium-regulated chloride channel function, subsequently other members of the family, such as TMEM16F, were found to have lipid scramblase activity combined with non-selective ion channel activity. TMEM16K was a relatively understudied member of the family despite the observation that mutations in TMEM16K have been linked to the genetic disease autosomal recessive spinocerebellar ataxia Type 10 (Also known as SCAR10 or ARCA3). SCAR10 is a late-onset neurodegenerative disorder which causes marked atrophy of the cerebellum with consequential deterioration in limb co-ordination, speech and eye movement. We have solved several structures of human TMEM16K through X-ray crystallography and cryo-EM capturing both active and inactive conformational states. Through collaborations, we have investigated TMEM16K’s function and location in cells. We were able to show that TMEM16K acts as a lipid scramblase with non-selective ion channel activity that is sensitive to both Ca²⁺ and lipid chain lengths. We also showed that TMEM16K mainly resides in the endoplasmic reticulum where it may be regulated by the ER’s unique lipid profile. Our highest resolution cryo-EM structure for TMEM16K allowed us to identify a bound lipid in the cavity behind the groove that transports the lipid headgroups and this lipid binding site may represent an allosteric modulator site, providing a direction for the design of binders which could modulate TMEM16K activity in cells.