# Bioinformatic, Enzymatic, and Structural Characterization of Trichuris suis Hexosaminidase HEX-2

## TL;DR

This paper characterizes a hexosaminidase enzyme from a pig parasite, revealing its structure and function, which helps understand this enzyme family better.

## Contribution

The study reports the first X-ray structure of a subfamily 1 GH20 hexosaminidase and reveals its unique substrate preferences and structural features.

## Key findings

- HEX-2 prefers aryl β-N-acetylgalactosaminide and has a neutral pH optimum.
- HEX-2 shows broader substrate specificity than insect hexosaminidases but narrower than plant homologues.
- The X-ray structure of HEX-2 is the first for subfamily 1 GH20 and reveals a key glutamate residue found in human hexosaminidases.

## Abstract

Hexosaminidases are key enzymes in glycoconjugate metabolism
and
occur in all kingdoms of life. Here, we have investigated the phylogeny
of the GH20 glycosyl hydrolase family in nematodes and identified
a β-hexosaminidase subclade present only in the Dorylaimia.
We have expressed one of these, HEX-2 from Trichuris
suis, a porcine parasite, and shown that it prefers
an aryl β-N-acetylgalactosaminide in
vitro. HEX-2 has an almost neutral pH optimum and is best
inhibited by GalNAc-isofagomine. Toward N-glycan substrates, it displays
a preference for the removal of GalNAc residues from LacdiNAc motifs
as well as the GlcNAc attached to the α1,3-linked core mannose.
Therefore, it has a broader specificity than insect fused lobe (FDL)
hexosaminidases but one narrower than distant homologues from plants.
Its X-ray crystal structure, the first of any subfamily 1 GH20 hexosaminidase
to be determined, is closest to Streptococcus pneumoniae GH20C and the active site is predicted to be compatible with accommodating
both GalNAc and GlcNAc. The new structure extends our knowledge about
this large enzyme family, particularly as T. suis HEX-2 also possesses the key glutamate residue found in human hexosaminidases
of either GH20 subfamily, including HEXD whose biological function
remains elusive.