Structure and mechanism of ADP‐ribose‐1″‐monophosphatase (Appr‐1″‐pase), a ubiquitous cellular processing enzyme

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Abstract
Appr‐1″‐pase, an important and ubiquitous cellular processing enzyme involved in the tRNA splicing pathway, catalyzes the conversion of ADP‐ribose‐1″monophosphate (Appr‐1″‐p) to ADP‐ribose. The structures of the native enzyme from the yeast and its complex with ADP‐ribose were determined to 1.9 Å and 2.05 Å, respectively. Analysis of the three‐dimensional structure of this protein, selected as a target in a structural genomics project, reveals its putative function and provides clues to the catalytic mechanism. The structure of the 284‐amino acid protein shows a two‐domain architecture consisting of a three‐layer αβα sandwich N‐terminal domain connected to a small C‐terminal helical domain. The structure of Appr‐1″‐pase in complex with the product, ADP‐ribose, reveals an active‐site water molecule poised for nucleophilic attack on the terminal phosphate group. Loop‐region residues Asn 80, Asp 90, and His 145 may form a catalytic triad.