Modulating the Structure and Function of an Aminoacyl-tRNA Synthetase Cofactor by Biotinylation

Arc1p is a yeast-specific tRNA-binding protein that forms a ternary complex with glutamyl-tRNA synthetase (GluRS(c)) and methionyl-tRNA synthetase (MetRS) in the cytoplasm to regulate their catalytic activities and subcellular distributions. Despite Arc1p not being involved in any known biotin-dependent reaction, it is a natural target of biotin modification. Results presented herein show that biotin modification had no obvious effect on the growth-supporting activity, subcellular distribution, tRNA binding, or interactions of Arc1p with GluRS(c) and MetRS. Nevertheless, biotinylation of Arc1p was temperature dependent; raising the growth temperature from 30 to 37 degrees C drastically reduced its biotinylation level. As a result, Arc1p purified from a yeast culture that had been grown overnight at 37 degrees C was essentially biotin free. Non-biotinylated Arc1p was more heat stable, more flexible in structure, and more effective than its biotinylated counterpart in promoting glutamylation activity of the otherwise inactive GluRS(c) at 37 degrees C in vitro. Our study suggests that the structure and function of Arc1p can be modulated via biotinylation in response to temperature changes.