From the Uncharacterized Protein Family 0016 to the GDT1 family: Molecular insights into a newly-characterized family of cation secondary transporters

Abstract

The Uncharacterized Protein Family 0016 (UPF0016) gathers poorly studied membrane proteins well conserved through evolution that possess one or two copies of the consensus motif Glu-x-Gly-Asp-(Arg/Lys)-(Ser/Thr). Members are found in many eukaryotes, bacteria and archaea. The interest for this protein family arose in 2012 when its human member TMEM165 was linked to the occurrence of Congenital Disorders of Glycosylation (CDGs) when harbouring specific mutations. Study of the UPF0016 family is undergone through the characterization of the bacterium Vibrio cholerae (MneA), cyanobacterium Synechocystis (SynPAM71), yeast Saccharomyces cerevisiae (Gdt1p), plant Arabidopsis thaliana (PAM71 and CMT1), and human (TMEM165) members. These proteins have all been identified as transporters of cations, more precisely of Mn 2+ , with an extra reported function in Ca 2+ and/or H + transport for some of them. Apart from glycosylation in humans, the UPF0016 members are required for lactation in humans, photosynthesis in plants and cyanobacteria, Ca 2+ signaling in yeast, and Mn 2+ homeostasis in the five aforementioned species. The requirement of the UPF0016 members for key physiological processes most likely derives from their transport activity at the Golgi membrane in human and yeast, the chloroplasts membranes in plants, the thylakoid and plasma membranes in cyanobacteria, and the cell membrane in bacteria. In the light of these studies on various UPF0016 members, this family is not considered as uncharacterized anymore and has been renamed the Gdt1 family according to the name of its S. cerevisiae member. This review aims at assembling and confronting the current knowledge in order to identify shared and distinct features in terms of transported molecules, mode of action, structure, etc., as well as to better understand their corresponding physiological roles.

Gene Replacement in Arabidopsis Reveals Manganese Transport as an Ancient Feature of Human, Plant and Cyanobacterial UPF0016 Proteins

“…Like PAM71, CMT1, MNX and TMEM165 are capable of transporting Mn 2+ into the thylakoid lumen for efficient reconstitution of inorganic Mn clusters in photosystem II (Figures 5C,D)-as demonstrated by the recovery of photosystem II efficiency (Figure 4C), which eventually increased plant growth (Figure 4B). A strong proton gradient across the thylakoid membrane (Hohner et al, 2016;Pottosin and Shabala, 2016) is established upon illumination, which presumably energizes Mn 2+ uptake into the acidic thylakoid lumen, in accordance with the current model of a cation/proton antiport mechanism for the UPF0016 protein family (Thines et al, 2020). In this respect, it is interesting to note that CMT1 can functionally replace PAM71 at the thylakoid membrane, but not vice versa (Figure 6 and Supplementary Figure 5).…”

“…Furthermore, we linked the PAM71 cTP sequence to the full-length TMEM165 sequence and replaced the original cTP sequence of CMT1 . An extended cTP sequence was used to generate the MNX construct, in order to increase the size of the protein ( Supplementary Figure 2 ), as the naturally occurring MNX/SynPAM71 is smaller than any of the other three proteins ( Thines et al, 2020 ). The five constructs were introduced into Agrobacterium cells and successfully transformed into the pam71 background.…”

“…The uncharacterized protein family 0016 (UPF0016), also referred to as the Gcr1-dependent translation factor1 (GDT1) family ( Thines et al, 2020 ), is a highly conserved membrane transporter family with members in many lineages of the tree of life ( Demaegd et al, 2014 ). One prominent member, which is responsible for the alternative family name just mentioned, is the Golgi-localized Gdt1p, originally identified as a Ca 2+ /H + antiporter in Saccharomyces cerevisiae ( Demaegd et al, 2013 ; Colinet et al, 2016 ).…”

“…Eukaryotic proteins of the UPF0016 family share a conserved overall structure, comprising two regions consisting of three transmembrane (TM) domains each, which are connected by an acidic loop, and contain a highly conserved Glu-x-Gly-Asp-(Arg/Lys)-(Ser/Thr) motif in TM1 and TM4, respectively ( Demaegd et al, 2014 ; Hoecker et al, 2017 ; Thines et al, 2020 ). This type—with six TM domains—is also found in many prokaryotes, while some others harbor one or two genes coding for a version that consists of only three TM domains, which are assumed to form homo- or heterodimers ( Demaegd et al, 2014 ).…”

Transport, functions, and interaction of calcium and manganese in plant organellar compartments

“…The Ca 2+ exchanger (CAX) family, reviewed by Pittman and Hirschi (2016) , contains both Ca 2+ -specific transporters and those transporting Ca 2+ and Mn 2+ ; both are energized by H + antiport ( Waight et al, 2013 ). The bivalent cation transporter (BICAT) family, with its chloroplast-localized members BICAT1 and BICAT2, has been identified only recently as a family of Ca 2+ /Mn 2+ transport proteins with a yet unresolved transport mechanism ( Thines et al, 2020 ). The inconsistent nomenclature of these transporters is explained in the chloroplast section of this review.…”