نبذة مختصرة : Human hyaluronidase 1 (HYAL1) and PH20 play vital roles in degrading hyaluronic acids through the substrate-assisted double displacement mechanism. While HYAL1, a lysosomal enzyme, functions optimally under acidic conditions, PH20, a sperm surface hyaluronidase, displays a broader pH range, from acidic to neutral. Our objective was to extend HYAL1's pH range towards neutral pH by introducing repulsive charge-charge interactions involving the catalytic Glu131, increasing its pKa as the proton donor. Substituting individual acidic residues in the β3-loop (S77D), β3'-β3″ hairpin (T86D and P87E), and at Ala132 (A132D and A132E) enabled HYAL1 to demonstrate enzyme activity at pH 7, with the mutants S77D, P87E, and A132E showing the highest activity in the substrate gel assay. However, double and triple substitutions, including S77D/T86D/A132E as found in the PH20 configuration, did not result in enhanced activity compared to single substitutions. Conversely, PH20 mutants with non-acidic substitutions, such as D94S in the β3-loop and D103T in the β3'-β3″ hairpin, significantly reduced activity within the pH range of 4 to 7. However, the PH20 mutant E149A, reciprocally substituted compared to A132E in HYAL1, exhibited activity similar to PH20 wild-type (WT) at pH 7. In a turbidimetric assay, HYAL1 mutants with single acidic substitutions exhibited activity similar to that of PH20 WT at pH 7. These results suggest that substituting acidic residues near Glu131 results in HYAL1 activity at neutral pH through electrostatic repulsion. This study highlights the significance of charge-charge interactions in both HYAL1 and PH20 in regulating the pH-dependent activity of hyaluronidases.
Competing Interests: M.G.C. is an employee of and holds shares in Odysgen Inc. A patent application titled "NEUTRAL pH-ACTIVE VARIANTS OF HYALURONIDASE HYAL1" has been submitted in Korea and through the PCT system by Odysgen Inc., based on the findings of this study (International publication number: WO2024005502A1). This does not alter our adherence to PLOS ONE policies on sharing data and materials
(Copyright: © 2024 Nguyen et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)
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