Pedobacter heparinus heparin lyase II (
PhHepII) is composed of N-terminal, central, and C-terminal domains. A long surface loop, designated loop-A, is in the N-terminal domain and is composed of amino acids 84-89. In this study, we deleted two, three, or four residues in loop-A to create Δ86-87, Δ85-87, and Δ84-87
PhHepII deletion mutants. We hypothesized that the deletions would increase
PhHepII thermostability. After heating purified
PhHepII enzymes at 45 °C for 5 min, 6.1 % of the enzyme activity remained in wild-type
PhHepII, whereas 10.6 % of the enzyme activity remained in Δ86-87
PhHepII. The results indicated that the deletion caused a significant decrease in the activity, although Δ86-87
PhHepII is slightly more thermostable than wild-type
PhHepII. In addtion, Δ85-87 and Δ84-87
PhHepII had weak or no enzyme activity, even when unheated. Circular dichroism spectra showed that Δ85-87
PhHepII was properly folded. These results suggest that the flexibility of loop-A is important for
PhHepII enzyme activity.
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