title: Oligomerization of the Mg2+-transport proteins Alr1p and Alr2p in yeast plasma membrane.
abstract: Alr1p is an integral plasma membrane protein essential for uptake of Mg(2+) into yeast cells. Homologs of Alr1p are restricted to fungi and some protozoa. Alr1-type proteins are distant relatives of the mitochondrial and bacterial Mg(2+)-transport proteins, Mrs2p and CorA, respectively, with which they have two adjacent TM domains and a short Mg(2+) signature motif in common. The yeast genome encodes a close homolog of Alr1p, named Alr2p. Both proteins are shown here to be present in the plasma membrane. Alr2p contributes poorly to Mg(2+) uptake. Substitution of a single arginine with a glutamic acid residue in the loop connecting the two TM domains at the cell surface greatly improves its function. Both proteins are shown to form homo-oligomers as well as hetero-oligomers. Wild-type Alr2p and mutant Alr1 proteins can have dominant-negative effects on wild-type Alr1p activity, presumably through oligomerization of low-function with full-function proteins. Chemical cross-linking indicates the presence of Alr1 oligomers, and split-ubiquitin assays reveal Alr1p-Alr1p, Alr2p-Alr2p, and Alr1p-Alr2p interactions. These assays also show that both the N-terminus and C-terminus of Alr1p and Alr2p are exposed to the inner side of the plasma membrane.
authors.affiliation: Max F. Perutz Laboratories, Department of Genetics, University of Vienna, Austria.
authors.forename: Marcin
authors.initials: M
authors.lastname: Wachek
authors.forename: Michael C
authors.initials: MC
authors.lastname: Aichinger
authors.forename: Jochen A
authors.initials: JA
authors.lastname: Stadler
authors.forename: Rudolf J
authors.initials: RJ
authors.lastname: Schweyen
authors.forename: Anton
authors.initials: A
authors.lastname: Graschopf
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry*; D008274:Magnesium / Q000378:metabolism*; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016133:Polymerase Chain Reaction; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism
chemical_list: C110206:ALR1 protein, S cerevisiae; C110207:ALR2 protein, S cerevisiae; D002352:Carrier Proteins; D027682:Cation Transport Proteins; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; D008274:Magnesium