Structures of vertebrate hyaluronidases and their unique enzymatic mechanism of hydrolysis |
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Authors: | Jedrzejas Mark J Stern Robert |
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Affiliation: | Children's Hospital Oakland Research Institute, Oakland, California 94609, USA. |
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Abstract: | Human hyaluronidases (Hyals) are a group of five endo-beta-acetyl-hexosaminidase enzymes, Hyal-1, -2, -3, -4, and PH-20, which degrade hyaluronan using a hydrolytic mechanism of action. Catalysis by these Hyals has been shown to follow a double-displacement scheme. This involves a single Glu residue within the enzyme, the only catalytic residue, as the proton donor (acid). Also involved is a carbonyl group of the hyaluronan (HA) N-acetyl-D-glucosamine as a unique type of nucleophile. Thus the substrate participates in the mechanism of action of its own catalysis. An oxocarbonium ion transition state is postulated, but there is no formation of a covalent enzyme-glycan intermediate, as found in most such reactions. The major domain is catalytic and has a distorted (beta/alpha)8 triose phosphate isomerase (TIM) barrel fold. The C-terminal domain is separated by a peptide linker. Each Hyal has a different C-terminal sequence and structure, the function of which is unknown. These unique C-termini may participate in the additional function(s) associated with these multifunctional enzymes. |
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Keywords: | chondroitin hyaluronan hyaluronidase mechanism of action modeling structure/function |
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