Plants contain small families of UPF0016 proteins including the PHOTOSYNTHESIS AFFECTED MUTANT71 transporter

Abstract

PHOTOSYNTHESIS AFFECTED MUTANT71 (PAM71) is an integral thylakoid membrane protein that functions in manganese uptake into the lumen. Manganese is needed in the thylakoid lumen to build up the inorganic MnCaO cluster, the catalytic center for water oxidation, and is hence indispensable for oxygen evolution. A recent study revealed that PAM71 is well conserved in plants and shares homology to GCR1 DEPENDENT TRANSLATION FACTOR1 (GDT1) and TRANSMEMBRANE PROTEIN 165 (TMEM165) in Saccharomyces cerevisiae and Homo sapiens, respectively. In most eukaryotes only single members of this family, designated "Uncharacterized Protein Family 0016" (UPF0016), are present; however, plant genomes contain genes for several UPF0016 proteins. In Arabidopsis thaliana, this protein family comprises 5 members, which mainly differ in their N-terminal regions. PAM71 and its closest homolog PAM71-HL possess chloroplast transit peptides at their N-terminus. Two of the remaining 3 members are derived from a segmental chromosomal duplication event and lack an N-terminal extension. Thus, plants have evolved UPF0016 members residing in various compartments of the cell, whereas in non-plant eukaryotes just a Golgi localization occurs. The identification of PAM71 as a candidate Mn transporter opens the question on the function of the remaining plant members. Here we resume briefly our current knowledge of UPF0016 members in Arabidopsis in comparison to their yeast and human UPF0016 members.

Manganese in Plants: From Acquisition to Subcellular Allocation

“…BICAT proteins, also denominated Photosynthesis-Affected Mutant71 (PAM71) or Chloroplast Manganese Transporter (CMT) proteins, belong to the Uncharacterized Protein Family 0016 (UPF0016), which represents a new family of cation transporters present in all eukaryotes and prokaryotes, except in Lactobacillales and Bacillales (Demaegd et al, 2013(Demaegd et al, , 2014Hoecker et al, 2017). The protein structure of the plant homologs is characterized by two clusters of three transmembrane domains separated by a central loop.…”

“…The protein structure of the plant homologs is characterized by two clusters of three transmembrane domains separated by a central loop. BICAT proteins act as Mn 2+ and Ca 2+ transporters (Hoecker et al, 2017;Frank et al, 2019).…”

Homologous Proteins of the Manganese Transporter PAM71 Are Localized in the Golgi Apparatus and Endoplasmic Reticulum

“…The UPF0016 family of membrane proteins comprises five members in Arabidopsis, and a sequence alignment is shown in Figure 1. PAM71 and CMT1 each contain a chloroplast-targeting signal (cTP) [8,10,23], whereas PML3 contains an N-terminal extension, which is predicted to be a secretory signal peptide (SP) [23] (Figure 1) and is notably lacking in PML4 and PML5 ( Figure 1). The five proteins each possess six conserved transmembrane domains and share two highly conserved E-x-G-D-(KR)-(TS) motifs in transmembrane domain TM1 and TM4.…”

“…According to the Transporter Classification Database (TCDB) [24] this protein family (classification number 2.A.106 in the TCDB) belongs to the LysE superfamily, this superfamily contains no other Mn transporters from plants. The three proteins PML3, PML4, and PML5 are predicted as substrates of the secretory pathway [10,23]. In the present study, we determined their subcellular localization and isolated insertion alleles.…”

“…In addition to PAM71 and CMT1, the Arabidopsis genome encodes three other members of the uncharacterized protein family 0016 (UPF0016) [23], which we refer here as PML for PAM71-like proteins: PML3 (encoded by At5g36290), PML4 (encoded by At1g25520) and PML5 (encoded by At1g68650). According to the Transporter Classification Database (TCDB) [24] this protein family (classification number 2.A.106 in the TCDB) belongs to the LysE superfamily, this superfamily contains no other Mn transporters from plants.…”