8.A.161. The Acyl Protein Thioesterase (APTE) Family
These enzymes hydrolyze fatty acids from S-acylated cysteine residues in proteins (Lin and Conibear 2015), and have depalmitoylating activity towards a variety of acylated proteins. S-Acylation, the reversible post-translational lipid modification of proteins, is important for control of the properties and functions of ion channels and other polytopic transmembrane proteins. McClafferty et al. 2020 showed that ABHD17a (alpha/beta-hydrolase domain-containing protein 17a) deacylates the stress-regulated exon domain of large conductance voltage- and calcium-activated potassium (BK) channels, inhibiting channel activity independently of effects on channel surface expression. ABHD17a (310 aas and 1 N-terminal TMS) deacylates BK channels in a site-specific manner because it has no effect on the S-acylated S0-S1 domains conserved in all BK channels that controls membrane trafficking and is deacylated by the acyl protein thioesterase Lypla1. Thus, distinct S-acylated domains in the same polytopic transmembrane protein can be regulated by different acyl protein thioesterases, revealing mechanisms for generating both specificity and diversity for these enzymes to control the properties and functions of ion channels (McClafferty et al. 2020). This family has two TC #s, the other being 4.C.3, and the ABHD17a thioesterase has TC#s 8.A.161.1.1 and.4.C.3.2.1.