PDBsum entry 1eq9

Hydrolase

PDB id: 1eq9

Contents

Protein chains

222 a.a. *

Ligands

PMS ×2

Waters ×529

* Residue conservation analysis

References listed in PDB file

Key reference

Title

The structure of an insect chymotrypsin.

Authors

I.Botos, E.Meyer, M.Nguyen, S.M.Swanson, J.M.Koomen, D.H.Russell, E.F.Meyer.

Ref.

J Mol Biol, 2000, 298, 895-901. [DOI no: 10.1006/jmbi.2000.3699]

PubMed id

10801356

Abstract

The South American imported fire ant (Solenopsis invicta), without natural enemies in the United States, widely infests the southern United States, causing more than a half billion dollars in health and agriculture-related damage annually in Texas alone. Fire ants are resistant to most insecticides, so control will require a more fundamental understanding of their biochemistry and metabolism leading to the design of selective, ecologically safe insecticides. The 4th instar larvae play a crucial role in the nutrition of the colony by secreting proteinases (especially chymotrypsin) which digest food products for the entire colony. The first structure of an ant proteolytic enzyme, fire ant chymotrypsin, was determined to atomic resolution (1.7 A). A structural comparison of the ant and mammalian structures confirms the "universality" of the serine proteinase motif and reveals a difference at residues 147-148, which are proteolytically removed in the bovine enzyme but are firmly intact in the ant chymotrypsin, suggesting a different activation mechanism for the latter. Likewise, the absence of the covalently attached propeptide domain (1-15) further suggests an uncharacteristic activation mechanism. The presence of Gly189 in the S1 site is an atypical feature of this chymotrypsin and is comparable only to human leukocyte elastase, hornet chymotrypsin and fiddler crab collagenase. Binding studies confirm the chymotrypsin nature of this novel enzyme.

Figure 1.
Figure 1. Structure of fire ant chymotrypsin C1. Stereo view of the 1.7 Å resolution structure of C1 superimposed on bovine aC (root mean square deviation 5.4 Å) shows the structural similarities and differences of their peptide scaffolds. The active site tetrad is shown, the aC propeptide is blue; peptide substrates bind from left (N terminus) to right. The arrowhead points to the backbone of residues 147-148. All structural Figures were created using program SPOCK [Christopher 1998].

Figure 3.
Figure 3. Omit F[o] - F[c] map of the catalytic residues contoured at 2.5s shows the strong, covalent binding of the inhibitor, PMSF. The orientation of Figure 1 is retained.

The above figures are reprinted by permission from Elsevier: J Mol Biol (2000, 298, 895-901) copyright 2000.