DEDUCED AMINO-ACID-SEQUENCE OF ESCHERICHIA-COLI ADENOSINE-DEAMINASE REVEALS EVOLUTIONARILY CONSERVED AMINO-ACID-RESIDUES - IMPLICATIONS FOR CATALYTIC FUNCTION

The goal of the research reported here is to identify evolutionarily conserved amino acid residues associated with enzymatic deamination of adenosine. To do this, we isolated molecular clones of the Escherichia coli adenosine deaminase gene by functional complementation of adenosine deaminase deficient bacteria and deduced the amino acid sequence of the enzyme from the nucleotide sequence of the gene. Nucleotide sequence analysis revealed the presence of a 996-nucleotide open reading frame encoding a protein of 332 amino acids having a molecular weight of 36 345. The deduced amino acid sequence of the E. coli enzyme has approximately 33% identity with those of the mammalian adenosine deaminases. With conservative amino acid substitutions the overall sequence homology approaches 50%, suggesting that the structures and functions of the mammalian and bacterial enzymes are similar. Additional amino acid sequence analysis revealed specific residues that are conserved among all three adenosine deaminases and four AMP deaminases for which sequence information is currently available. In view of previously published enzymological data and the conserved amino acid residues identified in this study, we propose a model to account for the enzyme-catalyzed hydrolytic deamination of adenosine. Potential catalytic roles are assigned to the conserved His 214, Cys 262, Asp 295, and Asp 296 residues of mammalian adenosine deaminases and the corresponding conserved amino acid residues in bacterial adenosine deaminase and the eukaryotic AMP deaminases.