CONFORMATIONAL FEATURES OF 5'-O-[N-(L-ALANYL)SULFAMOYL]ADENOSINE, A SUBSTRATE-ANALOG OF ALANYL-TRANSFER-RNA SYNTHETASE, STUDIED BY H-1-NMR AND ENERGY CALCULATION METHODS

The solution conformation of 5'-O-[N-(L-alanyl)sulfamoyl]adenosine (al a-SA), an analogue of alanyl-AMP, was studied by H-1-NMR spectroscopic and energy calculation methods for elucidating the substrate-specific ity of the cognate alanyl-tRNA synthetase. The ala-SA molecule existed in several conformational equilibria such as anti half arrow right ov er half arrow left syn, C3'-endo half arrow right over half arrow left C2'-endo and gauche.gauche half arrow right over half arrow left gauc he.trans (or trans-gauche) orientations concerning the glycosyl bond, ribose puckering and exocyclic C4'-C5' bond, respectively. However, th eir populations were solvent-dependent, and the major form in D2O solu tion could be characterized as the anti-C2'-endo-gauche-gauche conform ation, although no predominant conformation, except for C2'-endo ribos e puckering, existed in dimethyl sulfoxide solution. Possible conforme rs satisfying the NMR data were surveyed using empirical energy calcul ations, and the solution conformation of the ala-SA molecule was compa red with its crystal conformation.