Predicting the targeting of tail-anchored proteins to subcellular compartments in mammalian cells

Abstract

Tail-anchored (TA) proteins contain a single transmembrane domain (TMD) at the Cterminus, anchoring them to organelle membranes where they mediate a variety of critical cellular processes. Mutations in individual TA proteins cause a number of severe inherited disorders. However, the molecular mechanisms and signals facilitating proper TA protein targeting are not fully understood, in particular in mammals. Here, we identify additional TA proteins at peroxisomes or shared by multiple organelles in mammals and reveal that a combination of TMD hydrophobicity and tail charge determines targeting to distinct organelles. Specifically, an increase in tail charge can override a hydrophobic TMD signal and re-direct a protein from the ER to peroxisomes or mitochondria and vice versa. We demonstrate that subtle alterations in those physicochemical parameters can shift TA protein targeting between organelles, explaining why peroxisomes and mitochondria share many TA proteins. Our analyses enabled us to allocate characteristic physicochemical parameters to different organelle groups. This classification allows for the first time, successful prediction of the location of uncharacterized TA proteins.