Differential enzymatic activity of common haplotypic versions of the human acidic mammalian chitinase protein

Max A. Seibold, Tiffany A. Reese, Shweta Choudhry, Muhammad T. Salam, Kenny Beckman, Celeste Eng, Amha Atakilit, Kelley Meade, Michael Lenoir, H. Geoffrey Watson, Shannon Thyne, Rajesh Kumar, Kevin B. Weiss, Leslie C. Grammer, Pedro Avila, Robert P. Schleimer, John V. Fahy, Jose Rodriguez-Santan, William Rodriguez-Cintron, Rolf G. BootDean Sheppard, Frank D. Gilliland, Richard M. Locksley, Esteban G. Burchard

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


Mouse models have shown the importance of acidic mammalian chitinase activity in settings of chitin exposure and allergic inflammation. However, little is known regarding genetic regulation of AMCase enzymatic activity in human allergic diseases. Resequencing the AMCase gene exons we identified 8 non-synonymous single nucleotide polymorphisms including three novel variants (A290G, G296A, G339T) near the gene area coding for the enzyme active site, all in linkage disequilibrium. AMCase protein isoforms, encoded by two gene-wide haplotypes, and differentiated by these three single nucleotide polymorphisms, were recombinantly expressed and purified. Biochemical analysis revealed the isoform encoded by the variant haplotype displayed a distinct pH profile exhibiting greater retention of chitinase activity at acidic and basic pH values. Determination of absolute kinetic activity found the variant isoform encoded by the variant haplotype was 4-, 2.5-, and 10-fold more active than the wild type AMCase isoform at pH 2.2,4.6, and 7.0, respectively. Modeling of the AMCase isoforms revealed positional changes in amino acids critical for both pH specificity and substrate binding. Genetic association analyses of AMCase haplotypes for asthma revealed significant protective associations between the variant haplotype in several asthma cohorts. The structural, kinetic, and genetic data regarding the AMCase isoforms are consistent with the Th2-priming effects of environmental chitin and a role for AMCase in negatively regulating this stimulus.

Original languageEnglish (US)
Pages (from-to)19650-19658
Number of pages9
JournalJournal of Biological Chemistry
Issue number29
StatePublished - Jul 17 2009


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