1.A.35.2.1
Aluminum resistance protein Al^R1p; Alr1; ALR1, LLR1; MNR1 (Mg²⁺ homeostasis transporter [Mg²⁺ regulated]) Al^R1p and Al^R2p (P43553; a close paralogue) both catalyze uptake of Mg²⁺ and a variety of heavy metals (da Costa et al., 2007). Truncation of Alr1 showed that the N-terminal 239 amino acids and the C-terminal 53 amino acids are not essential for magnesium uptake (Lee and Gardner 2006). Mutations in the C-terminal part of ALR1 that is homologous to bacterial CorA magnesium transporters that gave severe phenotypes had amino acid changes in the small region containing the TMSs. Eighteen single amino acid mutants in this region were classified into three categories for magnesium uptake: no, low and moderate activity. Conservative mutations that reduced or inactivated uptake led to the identification of Ser(729), Ile(746) and Met(762) (part of the conserved GMN motif) as critical residues. High expression of inactive mutants inhibited the capability of wild-type Alr1 to transport magnesium, consistent with Alr1 forming homo-oligomers (Lee and Gardner 2006). Alr1 may play a role in cadmium resistance (Kern et al. 2005).