Reconstitution in vitro of the valyl-tRNA synthetase-elongation factor (EF) 1 beta gamma delta complex. Essential roles of the NH2-terminal extension of valyl-tRNA synthetase and of the EF-1 delta subunit in complex formation.
Valyl-tRNA synthetase from mammalian cells is isolated exclusively as a complex with elongation factor (EF) 1H (the "heavy" form of eukaryotic EF-1, composed of subunits alpha, beta, gamma, and delta). In a previous study, the 140-kDa valyl-tRNA synthetase subunit dissociated from the purified rabbit liver complex was shown to display hydrophobic properties, unlike the corresponding yeast cytoplasmic enzyme of 125 kDa (Bec, G., and Waller, J.-P. (1989) J. Biol. Chem. 264, 21138-21143). Compared to the sequence of yeast cytoplasmic valyl-tRNA synthetase, that of the human enzyme displays an NH2-terminal extension of approximately 200 amino acid residues that bears strong sequence similarity to the NH2-terminal moiety of EF-1 gamma (Hsieh, S. L., and Campbell, R. D. (1991) Biochem. J. 278, 809-816). We now show that this NH2-terminal extension can be selectively excised by elastase treatment of the isolated rabbit valyl-tRNA synthetase, without impairing catalytic activity. To examine the role of the NH2-terminal extension of mammalian valyl-tRNA synthetase in complex formation and to identify the subunit(s) of EF-1H responsible for binding the enzyme, reconstitution experiments were undertaken. Native or truncated valyl-tRNA synthetases were incubated with the isolated EF-1 subunits beta gamma and delta, either separately or in combination, and the ensuing products were analyzed by chromatography on DEAE-Sepharose FF and Superose 6. The results demonstrate that the NH2-terminal extension of valyl-tRNA synthetase is required for complex formation and that the enzyme-binding site(s) resides on the EF-1 delta subunit. Moreover, although the EF-1 beta gamma binary complex does not bind valyl-tRNA synthetase, it is nevertheless required for assembly of a complex of defined quaternary structure by preventing the formation of high molecular weight aggregates generated in the presence of EF-1 delta alone.
Bec
G
G
Laboratoire d'Enzymologie, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.
Kerjan
P
P
Waller
J P
JP
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D015186:Hominidae / Q000378:metabolism; D006801:Humans; D008099:Liver / Q000201:enzymology*; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010196:Pancreatic Elastase; D020648:Peptide Elongation Factor 1; D010445:Peptide Elongation Factors / Q000302:isolation & purification / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D011817:Rabbits; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D017386:Sequence Homology, Amino Acid; D014637:Valine-tRNA Ligase / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*
D046911:Macromolecular Substances; D020648:Peptide Elongation Factor 1; D010445:Peptide Elongation Factors; D010446:Peptide Fragments; D010196:Pancreatic Elastase; D014637:Valine-tRNA Ligase