1ll7
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STRUCTURE OF THE E171Q MUTANT OF C. IMMITIS CHITINASE 1
OverviewOverview
Allosamidin is a known inhibitor of class 18 chitinases. We show that, allosamidin is a competitive inhibitor of the fungal chitinase CiX1 from, Coccidioides immitis, with a K(i) of 60 nM. We report the X-ray structure, of the complex and show that upon inhibitor binding the side-chain of, Asp169 rotates to form an ion pair with the oxazolinium cation. The, mechanism of action is thought to involve protonation of the leaving group, by Glu171 and substrate assistance by the sugar acetamido moiety to form, an oxazoline-like intermediate. We converted both amino acid residues to, the corresponding amide and found that each mutation effectively abolishes, enzyme activity. X-ray structures show the mutant enzymes retain the basic, wild-type structure and that the loss of mutant activity is due to their, altered chemical properties. The high affinity of allosamidin, and its, similarity to the putative reaction intermediate, suggests it is a, transition state analog. This helps validate our contention that the role, of Asp169 is to electrostatically stabilize the reaction transition state.
About this StructureAbout this Structure
1LL7 is a Single protein structure of sequence from Coccidioides immitis. Active as Chitinase, with EC number 3.2.1.14 Full crystallographic information is available from OCA.
ReferenceReference
The structure of an allosamidin complex with the Coccidioides immitis chitinase defines a role for a second acid residue in substrate-assisted mechanism., Bortone K, Monzingo AF, Ernst S, Robertus JD, J Mol Biol. 2002 Jul 5;320(2):293-302. PMID:12079386
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