Identification of essential residues in 2',3'-cyclic nucleotide 3'-phosphodiesterase. Chemical modification and site-directed mutagenesis to investigate the role of cysteine and histidine residues in enzymatic activity.
2',3'-Cyclic nucleotide 3'-phosphodiesterase (CNP; EC ) catalyzes in vitro hydrolysis of 3'-phosphodiester bonds in 2',3'-cyclic nucleotides to produce 2'-nucleotides exclusively. N-terminal deletion mapping of the C-terminal two-thirds of recombinant rat CNP1 identified a region that possesses the catalytic domain, with further truncations abolishing activity. Proteolysis and kinetic analysis indicated that this domain forms a compact globular structure and contains all of the catalytically essential features. Subsequently, this catalytic fragment of CNP1 (CNP-CF) was used for chemical modification studies to identify amino acid residues essential for activity. 5,5'-Dithiobis-(2-nitrobenzoic acid) modification studies and kinetic analysis of cysteine CNP-CF mutants revealed the nonessential role of cysteines for enzymatic activity. On the other hand, modification studies with diethyl pyrocarbonate indicated that two histidines are essential for CNPase activity. Consequently, the only two conserved histidines, His-230 and His-309, were mutated to phenylalanine and leucine. All four histidine mutants had k(cat) values 1000-fold lower than wild-type CNP-CF, but K(m) values were similar. Circular dichroism studies demonstrated that the low catalytic activities of the histidine mutants were not due to gross changes in secondary structure. Taken together, these results demonstrate that both histidines assume critical roles for catalysis.
Department of Biochemistry, McGill University, Montreal, Quebec H3G 1Y6, Canada.
J
J
Lee
M
M
Gravel
E
E
Gao
R C
RC
O'Neill
P E
PE
Braun
D063309:2',3'-Cyclic Nucleotide 3'-Phosphodiesterase; D015087:2',3'-Cyclic-Nucleotide Phosphodiesterases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D020134:Catalytic Domain; D003545:Cysteine / Q000378:metabolism*; D017931:DNA Primers; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006639:Histidine / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010727:Phosphoric Diester Hydrolases; D051381:Rats; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D017931:DNA Primers; D004791:Enzyme Inhibitors; D011994:Recombinant Proteins; D006639:Histidine; D004228:Dithionitrobenzoic Acid; D015087:2',3'-Cyclic-Nucleotide Phosphodiesterases; D010727:Phosphoric Diester Hydrolases; D063309:2',3'-Cyclic Nucleotide 3'-Phosphodiesterase; C571339:Cnp protein, rat; D003545:Cysteine