Increasing intracellular magnesium levels with the 31-amino acid MgtS protein

Significance Proteins of fewer than 50 amino acids are overlooked by most genomic and biochemical approaches and their functions are generally unknown. Here we report that a 31-amino acid inner membrane protein synthesized in response to limiting Mg 2+ binds and stabilizes the major Mg 2+ importer, thereby leading to increased intracellular levels of this critical ion. This discovery further supports the hypothesis that many of these overlooked small proteins regulate the functions and stabilities of larger membrane proteins.