Functional analysis of a Hansenula polymorpha MNN2-2 homologue encoding a putative UDP-N-acetylglucosamine transporter localized in the endoplasmic reticulum

Ero1-Pdi1 module-catalysed dimerization of a nucleotide sugar transporter, FonNst2, regulates virulence of Fusarium oxysporum on watermelon

Fusarium oxysporum f. sp. niveum (Fon) is a soil-borne fungus causing vascular Fusarium wilt on watermelon; however, the molecular network regulating Fon virulence remains to be elucidated. Here, we report the function and mechanism of nucleotide sugar transporters (Nsts) in Fon. Fon genome harbours nine FonNst genes with distinct functions in vegetative growth, asexual production, cell wall stress response and virulence. FonNst2 and FonNst3 are required for full virulence of Fon on watermelon and FonNst2 is mainly involved in fungal colonization of the plant tissues. FonNst2 and FonNst3 form homo- or hetero-dimers but function independently in Fon virulence. FonNst2, which has UDP-galactose transporter activity in yeast, interacts with FonEro1 and FonPdi1, both of which are required for full virulence of Fon. FonNst2, FonPdi1 and FonEro1 target to endoplasmic reticulum (ER) and are essential for ER homeostasis and function. FonEro1-FonPdi1 module catalyses the dimerization of FonNst2, which is critical for Fon virulence. Undimerized FonNst2 is unstable and degraded via ER-associated protein degradation in vivo. These data demonstrate that FonEro1-FonPdi1 module-catalysed dimerization of FonNst2 is critical for Fon virulence on watermelon and provide new insights into the regulation of virulence in plant fungal pathogens via disulfide bond formation of key pathogenicity factors.

Evaluation of Ogataea (Hansenula) polymorpha for Hyaluronic Acid Production

Hyaluronic acid (HA) is a biopolymer formed by UDP-glucuronic acid and UDP-N-acetyl-glucosamine disaccharide units linked by β-1,4 and β-1,3 glycosidic bonds. It is widely employed in medical and cosmetic procedures. HA is synthesized by hyaluronan synthase (HAS), which catalyzes the precursors’ ligation in the cytosol, elongates the polymer chain, and exports it to the extracellular space. Here, we engineer Ogataea (Hansenula) polymorpha for HA production by inserting the genes encoding UDP-glucose 6-dehydrogenase, for UDP-glucuronic acid production, and HAS. Two microbial HAS, from Streptococcus zooepidemicus (hasAs) and Pasteurella multocida (hasAp), were evaluated separately. Additionally, we assessed a genetic switch using integrases in O. polymorpha to uncouple HA production from growth. Four strains were constructed containing both has genes under the control of different promoters. In the strain containing the genetic switch, HA production was verified by a capsule-like layer around the cells by scanning electron microscopy in the first 24 h of cultivation. For the other strains, the HA was quantified only after 48 h and in an optimized medium, indicating that HA production in O. polymorpha is limited by cultivation conditions. Nevertheless, these results provide a proof-of-principle that O. polymorpha is a suitable host for HA production.

Nucleotide sugar transporters of Entamoeba histolytica and Entamoeba invadens involved in chitin synthesis

Chitin, a homopolymer of β-(1,4) linked N-acetylglucosamine (GlcNAc), is a major component of cyst wall in the protozoan parasites Entamoeba histolytica (Eh) and Entamoeba invadens (Ei). The Entamoeba chitin synthase makes chitin at the vesicular membrane rather than the plasma membrane in fungi, even though the chemistry of chitin synthesis is most likely the same. However, the role of nucleotide sugar transporter(s) (NSTs) that are involved in chitin synthesis in Entamoeba are not yet established. In this study, we have identified the putative UDP-GlcNAc transporter (EiNst5) of Ei by BLASTP analysis using the amino acid sequence of EhNst3, the UDP-GlcNAc transporter of Eh. Heterologous expression of both EhNst3 and EiNst5 was found to complement the function of Yea4p (UDP-GlcNAc transporter of S. cerevisiae) in YEA4 null mutant and increased the cell wall chitin content. Like Yea4p in S. cerevisiae, Myc-epitope tagged EhNst3 and EiNst5 were localized to the endoplasmic reticulum in Δyea4 cells. The EiNST5 transcript was up-regulated during the in vitro encystation and oxidative stress in E. invadens. Similar up-regulation was also seen for EhNST3 under oxidative stress in E. histolytica. Down-regulation of EiNst5 expression using gene-specific dsRNA significantly reduced cyst formation during in vitro encystation in E. invadens. Our observations suggest for the first time the involvement of EhNst3 and EiNst5 in chitin synthesis and so in encystation of Entamoeba.