Nat. Struct. Mol. Biol. 11, 412–419 (2004).
Some of the enzymatic activity data for paraoxonase (PON1) reported in this article were biased by two factors. First, the gene encoding the H115Q mutant contained an additional H177R mutation introduced during PCR amplification. Although His177 is far from the active site and the H177R mutant by itself is 70% active compared to the wild-type PON1, the combined H115Q H177R mutant is almost completely inactive. Second, the H115Q and the H134Q mutants are unstable and prone to misfolding and thus aggregation.
We have now generated the H115Q mutant without the interfering H177R mutation. We have also modified the purification protocol to include 10% (v/v) glycerol and 0.1% (v/v) tergitol in the lysis, loading and elution buffers. The activities of both the H115Q and the H134Q mutants are assayed immediately after purification. For comparison, we also generated another mutant (H115W) that has been studied recently by Yeung et al. (Biochim. Biophys. Acta 1702, 67–77, 2004) and assayed its activity. The activity data for these mutants under the revised conditions are reported below:
When these same mutations are incorporated into the recombinant PON1 variant G2E6, the structure of which was determined and reported in the article, and into another recombinant PON1 variant (G3C9; see Table 1 of the article), we obtained similar activity data as above (not shown). These results indicate that His115 and His134 are responsible for the aryl-esterase activity but not the paraoxonase activity of PON1. Thus, the two hydrolytic activities may be catalyzed by different active site residues, and the model postulated in the article may be valid only for the aryl-esterase activity. We apologize for any inconvenience this may have caused.
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