Origin and evolution of Auxin Efflux Carrier family: PIN, PILS, GPR155 and the others

Abstract The resolution of the 3D structure of PIN proteins and the ability to universally predict protein structures using AlphaFold allowed us to reconsider the classification of Auxin efflux carriers within the BART superfamily, and we propose to merge members of this superfamily, possessing a characteristic fold with a helical crossover, with other families carrying this fold (BASS, NhaA, CPA and others) into a newly proposed superfamily named X-Helices Carriers (XHC). We further demonstrate a profound divergence between PIN and PILS proteins and monophyly of eukaryotic PINs with the animal cholesterol receptor GPR155/LYCHOS. We hypothesise that its signalling capacity is derived from a general feature of PIN proteins to interact with membrane lipids within the core membrane fold. Finally, we discuss the auxin-transport ability of PIN and PILS proteins in the context of the described properties of bacterial homologs that act as organic acid permeases. Disclaimer This version is a draft and it will be updated during the next few weeks. Highlights PINs are in plants and fragmentary in many algae and protists, but never in fungi Eukaryotic PINs are monophyletic together with animal cholesterol receptor GPR155 PILS are frequently present in protists and in all fungi, but not in animals PINs/PILS split is occurred very early in Prokaryota AECs belongs to proposed superfamily of transporter with helical crossover Competing Interest Statement The authors have declared no competing interest.