Two-dimensional transferred nuclear Overhauser effect spectroscopy (TRNOESY) studies of nucleotide conformations in arginine kinase complexes.

Abstract

Two-dimensional proton transfer nuclear Overhauser spectroscopy (TRNOESY) studies of the conformations of the adenosine moieties in the nucleotides bound at the active site of the lobster (Homarus americanus) muscle arginine kinase are reported. TRNOESY measurements were made using a sample protocol chosen to minimize contributions from weak non-specific binding of the nucleotides to the observed NOE's. This was done by making the measurements as a function of ligand concentration while keeping the ligand to enzyme concentration ratio fixed at 10:1. The experiments were performed at 500 MHz and 10 degrees C for six different mixing times in the range 40-300 ms. The measurements were made on three complexes of the enzyme: E.MgATP, E.MgADP, and the long-lived transition-state-analog complex (E.MgADP.NO-3.arginine). All the complexes, including the transition-state-analog complex with an estimated lifetime of about 50 ms, satisfy the fast-exchange condition. The TRNOE buildup curves for all the nucleotide-proton pairs in each complex were analyzed using a complete relaxation matrix appropriate for fast exchange. The interproton distances obtained from the NOE analysis were used as constraints in obtaining an energy-minimized conformation on the basis of the program CHARMm. The glycosidic torsion angle (chi) for the adenosine moiety in all three complexes is about 50 degrees +/- 5 degrees. The glycosidic orientation agrees well with that determined for MgATP and MgADP complexes of creatine kinase (Murali et al., 1993), MgATP bound at the active and ancillary sites of pyruvate kinase (Jarori et al., 1994a), and PRPP synthetase (Jarori et al., 1994b).(ABSTRACT TRUNCATED AT 250 WORDS)