Genetic, enzymatic, and structural analyses of phenylalanyl-tRNA synthetase from Thermococcus kodakaraensis KOD1

Phenylalanyl-tRNA synthetase from the hyperthermophilic archaeon Thermococcus kodakaraensis KOD1 (Tk-PheRS) was cloned. The open reading frames for both the alpha-subunit (Tk-pheRSA) and beta-subunit (Tk-pheRSB) genes were 1,503 bp (501 amino acids) and 1,722 bp (574 amino acids), respectively. Tk-pheRSB located 879 bp downstream from Tk-pheRSA with a putative TATA box, suggesting that these two subunits are transcribed and regulated independently in KOD1 cells. Tk-PheRS and its respective subunits were expressed in Escherichia coli cells and the proteins were purified. Tk-PheRS showed an optimum enzymatic activity at around 95 degrees C and retained its tertiary structure at 98 degrees C. The estimated isoelectric point (pI) for the alpha-subunit is 9.4 and that for the beta-subunit is 4.6, the largest difference among the 12 kinds of PheRSs reported. The considerable thermostability of Tk-PheRS may be responsible for the electrostatic interaction between the alpha- and beta-subunits.