TRNA/Aminoacyl-tRNA Synthetase Interactions

Abstract

Aminoacyl-tRNA synthetases (aaRS) bring together amino acids and their cognate tRNAs. In the reaction, the amino acid is esterified to one of the hydroxyl groups of the 3′-terminal adenosine of the tRNA via an aminoacyl-adenylate intermediate, and the energy in the overall reaction is supplied by the hydrolysis of ATP (Schimmel and Soll 1979). Generally, there is one aaRS for each amino acid, which may in turn be specified by several isoacceptor tRNA species (Yarus 1972; Schimmel and Soll 1979). The subject of aaRS was recently reviewed by Carter (1993) and Meinnel et al. (1995). aaRS are a diverse family of enzymes, whose quaternary structures range from monomeric to dimeric to tetrameric (Table 1); still, the family represents two structural and functional solutions to the organization of the active-site domain, which makes it possible to group these enzymes into two classes of 10 members each (Eriani et al. 1990b; Ruff et al. 1991). The active sites of class I aaRS harbor signature amino acid sequences KMSKS and HIGH (Fig. 1A). Their structures contain the Rossmann fold nucleotide-binding motif, an alternating α-β structure with a central parallel β-sheet (Rossmann et al. 1974). These aaRS attach the amino acid to the 2′-OH of the 3′-terminal ribose (Sprinzl and Cramer 1975). The active sites of class II aaRS have three concatenated homologous sequence motifs 1, 2, and 3 (Fig. 1B). Their structures are based on an antiparallel β-sheet (Moras 1992; Delarue and Moras 1993); so far this fold has only been found in...