Recognition of different nucleotidyl-derivatives as substrates of reactions catalyzed by various HIT-proteins

Proteins that have a histidine triad in their active sites belong to the HIT-protein superfamily. They are ubiquitous, are involved in the metabolism of different nucleotides and catalyze their hydrolysis and/or phosphorolysis liberating either the corresponding 5′-NMP or 5′-NDP, respectively. We studied substrate specificity of nine recombinant HIT-proteins with adenosine 5′-phosphosulfate (1), adenosine 5′-phosphoramidate (2), adenosine 5′-phosphorothioate (3), adenosine 5′-phosphorofluoride (4), diadenosine 5′,5′′′-P1,P3-triphosphate (5), di(7-methylguanosine) 5′,5′′′-P1,P3-triphosphate (6) and adenosine 5′-hypophosphate (7). Preferences for the recognition of these compounds as substrates by individual proteins differed. All the proteins hydrolyzed (1) but the Arabidopsis thaliana Hint1 did it very slowly. None of the proteins cleaved (7). Only A. thaliana Hint1 and Escherichia coli HinT hydrolyzed (3). Three proteins known as dinucleoside triphosphatases, human and A. thaliana Fhit-proteins and Trypanosoma brucei HIT-45, cleaved (1), (2), (4), (5) and (6). Caenorhabditis elegans decapping protein DcpS degraded (1), (5), (6) and poorly (4). A. thaliana aprataxin-like protein and Hint4 hydrolyzed only (1), (2) and (4), in that order of efficiency. Velocities of those reactions and some Km values were determined. Applicability of this study to the metabolism of certain nucleotidyl-derivatives is discussed.