NMR studies of a complex of RNAse from Penicillium brevicompactum with dinucleoside phosphonate and the implications for the mechanism of enzyme action.
The chemical-shift dependences of the proton signals of the guanosine and uridine moieties were measured as a function of the relative amount of GpcU complexed with RNase Pb1 (EC 3.1.27.3). The equal values of the chemical-shift changes of the guanosine C8-protons on complex formation between GpcU and RNase Pb1 and that of the 3'-GMP and RNase Pb1 allow to conclude that the guanosine base is bound in the same manner in these protein-ligand complexes. The guanosine moiety of GpcU is also most probably bound in the syn-conformation. The absence of changes in both the linewidths and the chemical shifts of the C1', C5 and C6-proton signals of the uridine on complex formation indicates that the uridine moiety of the dinucleoside phosphonate is not immobilized in the complex. The pH dependences of the chemical shifts of the C2-protons of the histidine-imidazole ring of RNase Pb1 and that of the 31P of GpcU in the RNase complex were studied. The results suggest that there is a direct interaction between the phosphonate group of the ligand and the protonated imidazole ring of His-90. The side groups of His-38 and Glu-56 are hydrogen bonded to each other at neutral pH and they are located in the vicinity of the phosphonate group of GpcU. When the carboxyl group of Glu-56 is protonated the His-38 imidazole ring forms a new hydrogen bond with one of the phosphoryl oxygens of the phosphonate group. On the basis of these results we propose the mechanism of action of RNase Pb1 which is probably also true for RNase T1.
Yakovlev
G I
GI
Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow.
Moiseyev
G P
GP
D001230:Aspergillus / Q000201:enzymology; D001665:Binding Sites; D015226:Dinucleoside Phosphates / Q000737:chemistry*; D005971:Glutamates / Q000737:chemistry; D018698:Glutamic Acid; D006639:Histidine / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D010407:Penicillium / Q000201:enzymology*; D012260:Ribonucleases / Q000737:chemistry* / Q000378:metabolism
D015226:Dinucleoside Phosphates; D005971:Glutamates; D018698:Glutamic Acid; C018310:guanylyl-(3'-5')-uridine; D006639:Histidine; D012260:Ribonucleases