STRUCTURAL-ANALYSIS OF THE HIGH MOLECULAR MASS AMINOACYL-TRANSFER RNA-SYNTHETASE COMPLEX - EFFECTS OF NEUTRAL SALTS AND DETERGENTS

The effects of a variety of detergents and neutral salts on the structure of the eukaryotic high molecular mass aminoacyl-tRNA synthetase complex have been directly determined by observing alterations in the composition, sedimentation behavior, and electron microscopic appearance of the rabbit reticulocyte complex. The intact complex is shown to exhibit the enzymatic activities, polypeptide composition, relative stoichiometry, and morphological features that are characteristic of this eukaryotic multienzyme particle. The structure of the high molecular mass aminoacyl-tRNA synthetase complex is seen to be resistant to both ionic and nonionic detergents. However, both 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate and deoxycholate induce formation of large protein aggregates. In contrast, the chaotropic salts LiCl and NaSCN both selectively remove individual polypeptides from the high molecular mass aminoacyl-tRNA synthetase complex and promote formation of specific particulate subcomplexes which have distinct sizes, polypeptide compositions, and structural features. These data support the view that many of the protein interactions within the high molecular mass aminoacyl-tRNA synthetase complex are hydrophobic in nature. This study also provides direct evidence that the complex contains a core of tightly interacting synthetases onto which the remaining polypeptides are arrayed. The structural alterations observed here may account for the ability of these reagents to markedly inhibit several enzymatic activities within the complex.