# Expression and molecular characterization of an intriguing hyaluronan synthase (HAS) from the symbiont “Candidatus Mycoplasma liparidae” in snailfish

## TL;DR

This study explores a new hyaluronan synthase from a deep-sea snailfish symbiont, revealing its unique properties for producing low molecular weight hyaluronic acid efficiently.

## Contribution

The paper reports the first characterization of a hyaluronan synthase from a deep-sea symbiont with distinct structural and kinetic features.

## Key findings

- snHAS lacks transmembrane regions and does not fit into known HAS classes.
- snHAS produces low molecular weight hyaluronic acid more efficiently than mammalian HAS.
- snHAS activity is not influenced by cardiolipin, unlike some other HAS enzymes.

## Abstract

Hyaluronan synthases (HASs) are ubiquitous in living organisms, and the hyaluronic acid (HA) synthesized by them are important to their body and well used in medicine, cosmetics and other fields. HAS from deep-sea creatures has not yet been explored before. The study aims to analyse the characteristics and enzyme kinetics of a novel hyaluronan synthase derived from the symbiont “Candidatus Mycoplasma liparidae” found in deep-sea snailfish (snHAS).

snHAS was over-expressed using His 6 as tag in the study. The sequence alignment was conducted by Cluster W and then the phylogenetic analyse of HASs was performed by Mega 6.0 to investigate the position of snHAS during evolution. Km and Vmax were detected to study the enzyme kinetics of snHAS wildtype and its mutant. The molecular weight of HA was evaluated by high performance gel permeation chromatography (HPGPC). The cardiolipin was added to investigate whether it had a promoting effect on the snHAS.

The length of snHAS was 933 bp with an open reading frame (ORF) of 310 amino acids. Unlike other repoted HASs, snHAS had no transmembrane region and was not classified into the currently known Class I or Class II. snHAS could synthesize hyaluronan with lower molecular weights using the substrates of uridine-diphosphate—N-acetylglucosamine (UDP-GlcNAc) and uridine-diphosphate—glucuronic acid (UDP-GlcA) in vitro. The Km values of snHAS were 258 ± 45 µM and 39 ± 5 µM for UDP-GlcNAc and UDP-GlcA, respectively, much lower than those from mice (Km for UDP-GlcA: 55 ± 5 µM; Km for UDP-GlcNAc: 870 ± 60 µM). The kcat/Km values of snHAS were 163.5 s−1 mM−1 and 8.08 s−1 mM−1 for UDP-GlcA and UDP-GlcNAc, respectively. Furthermore, the activity of snHAS was independent of cardiolipin.

snHAS was a novel HAS based on the characteristics of the animo acid sequence, which could produce low molecular weight of HA with high efficiency. This provides a molecular basis for the biosynthesis of low molecular weight of HA.