$^{15}$N NMR Relaxation Study of the Catalytic Residues in Y14F Mutant Ketosteroid Isomerase

  • Yoon, Ye-Jeong (Department of Chemistry/Division of Molecular and Life Sciences Pohang Universtity of Science and Technology) ;
  • Lee, Hyeong-Ju (Department of Chemistry/Division of Molecular and Life Sciences Pohang Universtity of Science and Technology) ;
  • Kim, Chul (Department of Chemistry/Division of Molecular and Life Sciences Pohang Universtity of Science and Technology) ;
  • Lee, Hee-Cheon (Department of Chemistry/Division of Molecular and Life Sciences Pohang Universtity of Science and Technology)
  • 발행 : 2004.12.20

초록

$^1$H-detected $^{15}$N NMR was employed to investigated the effect of mutation (Y14F) on the dynamic properties of catalytic residues in ${\Delta}^5$-3- ketosteroid isomerase (KSI) from Conamonas testosteroni. In particular, the backbone dynamics of the catalytic residues have been studied in free enzyme and its complex with a steroid ligand, 19-nortestosterone hemisuccinate, by $^{15}$N relaxation measurements. The relaxation data were analyzed using the model-free formalism to extract the model-free parameters (S$^2$, ${\tau}_e$, and R$_{ex}$). The results show that the mutation causes a significant decrease in the order parameter (S$^2$) for the catalytic residues of free Y14F KSI, presumably due to breakdown of the hydrogen bond network by mutation. In addition, the order parameters of Phe-14 and Asp-99 increased slightly upon ligand binding, indicating a slight restriction of the high-frequency (pico- to nanosecond) internal motions of the residues in the complexed Y14F KSI, while the order parameter of Tyr-55 decreased significantly upon ligand binding.

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