Characterization of the tryptophan residues of human placental ribonuclease inhibitor and its complex with bovine pancreatic ribonuclease A by steady-state and time-resolved emission spectroscopy.
Human placental ribonuclease inhibitor (hRI) containing six tryptophan (Trp) residues located at positions 19, 261, 263, 318, 375, and 438 and its complex with RNase A have been studied using steady-state and time-resolved fluorescence (298 K) as well as low-temperature phosphorescence (77 K). Two Trp residues in wild-type hRI and also in the protein-protein complex with RNase A are resolved optically. The accessible surface area values of Trp residues in the wild-type hRI and its complex and consideration of inter-Trp energy transfer in the wild-type hRI reveal that one of the Trp residues is Trp19, which is located in a hydrophobic buried region. The other Trp residue is tentatively assigned as Trp375 based on experimental results on wild-type hRI and its complex. This residue in the wild-type hRI is more or less solvent exposed. Both the Trp residues are perturbed slightly on complex formation. Trp19 moves slightly toward a more hydrophobic region, and the environment of Trp375 becomes less solvent exposed. The complex formation also results in a more heterogeneous environment for both the optically resolved Trp residues.
Sardar
Pinki Saha
PS
Department of Chemistry, Presidency College, Calcutta 700073, India.
Maity
Shyam Sundar
SS
Ghosh
Sanjib
S
Chatterjee
Juin
J
Maiti
Tushar Kanti
TK
Dasgupta
Swagata
S
D000818:Animals; D002417:Cattle; D004735:Energy Transfer; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D010926:Placental Hormones / Q000737:chemistry*; D012259:Ribonuclease, Pancreatic / Q000737:chemistry*; D013057:Spectrum Analysis; D014364:Tryptophan / Q000737:chemistry*
D010926:Placental Hormones; C022052:placental ribonuclease inhibitor; D014364:Tryptophan; D012259:Ribonuclease, Pancreatic