Structural Superimposition

Abstact

Pch-GlmA is a hyperthermophilic GH35 exo-beta-d-glucosaminidase whose structure closely resembles its archaeal homologs, yet its functional behavior differs markedly. Calorimetric and fluorimetric temperature scans consistently reveal a complex thermodynamic profile of the enzyme, characterized by distinct thermal transitions. The freshly purified protein appears to be monomeric and required thermal annealing to attain its biologically relevant dimeric state. Catalytic activity is observed only above 75 degrees C, where the enzyme specifically hydrolyses the glycosidic bond of GlcN-GlcNAc. These findings support a sequential role for Pch-GlmA alongside Pch-Dac in the processing of chitin-derived carbohydrates. Comparison with related GlmA proteins demonstrates that substantial structural similarity does not necessarily translate into equivalent enzymatic properties and that hyperthermophilic enzymes may operate within narrow temperature ranges. Overall, this work underscores the importance of experimental validation when interpreting or predicting the activity of enzymes derived from extremophiles.