Hansenula polymorpha Pmt4p Plays Critical Roles in O-Mannosylation of Surface Membrane Proteins and Participates in Heteromeric Complex Formation

A Split-Marker System for CRISPR-Cas9 Genome Editing in Methylotrophic Yeasts

Methylotrophic yeasts such as Ogataea polymorpha and Komagataella phaffii (sin. Hansenula polymorpha and Pichia pastoris, respectively) are commonly used in basic research and biotechnological applications, frequently those requiring genome modifications. However, the CRISPR-Cas9 genome editing approaches reported for these species so far are relatively complex and laborious. In this work we present an improved plasmid vector set for CRISPR-Cas9 genome editing in methylotrophic yeasts. This includes a plasmid encoding Cas9 with a nuclear localization signal and plasmids with a scaffold for the single guide RNA (sgRNA). Construction of a sgRNA gene for a particular target sequence requires only the insertion of a 24 bp oligonucleotide duplex into the scaffold. Prior to yeast transformation, each plasmid is cleaved at two sites, one of which is located within the selectable marker, so that the functional marker can be restored only via recombination of the Cas9-containing fragment with the sgRNA gene-containing fragment. This recombination leads to the formation of an autonomously replicating plasmid, which can be lost from yeast clones after acquisition of the required genome modification. The vector set allows the use of G418-resistance and LEU2 auxotrophic selectable markers. The functionality of this setup has been demonstrated in O. polymorpha, O. parapolymorpha, O. haglerorum and Komagataella phaffii.

Hyperosmotic medium partially restores the growth defect and the impaired production of sterigmatocystin of an Aspergillus nidulans ΔpmtC mutant in a HogA-independent manner

The protein O-mannosyltransferase catalyzes O-mannosylation in the endoplasmic reticulum by transferring mannose to the seryl or threonyl residues of substrate proteins. We previously reported a deletion mutant of O-mannosyltransferase C (ΔpmtC) in Aspergillus nidulans with impaired vegetative growth and sterigmatocystin (ST) production. In this study, we investigated whether osmotic conditions contribute to the developmental processes and ST biosynthesis of the ΔpmtC deletion mutant. We found that hyphal growth and ST production partially improved in the presence of NaCl, KCl or sorbitol as osmotic stabilizers. Conidiation of the ΔpmtC deletion mutant was not restored under osmotic stress conditions when the hogA gene was deleted. The hogA gene encodes a protein required for the cellular response to osmotic pressure. However, the yield of ST and the vegetative growth of the ΔhogA ΔpmtC double deletant was restored by high osmolarity in a HogA-independent manner.

Pentose metabolism and conversion to biofuels and high-value chemicals in yeasts

Pentose sugars are widespread in nature and two of them, D-xylose and L-arabinose belong to the most abundant sugars being the second and third by abundance sugars in dry plant biomass (lignocellulose) and in general on planet. Therefore, it is not surprising that metabolism and bioconversion of these pentoses attract much attention. Several different pathways of D-xylose and L-arabinose catabolism in bacteria and yeasts are known. There are even more common and really ubiquitous though not so abundant pentoses, D-ribose and 2-deoxy-D-ribose, the constituents of all living cells. Thus, ribose metabolism is example of endogenous metabolism whereas metabolism of other pentoses, including xylose and L-arabinose, represents examples of the metabolism of foreign exogenous compounds which normally are not constituents of yeast cells. As a rule, pentose degradation by the wild-type strains of microorganisms does not lead to accumulation of high amounts of valuable substances; however, productive strains have been obtained by random selection and metabolic engineering. There are numerous reviews on xylose and (less) L-arabinose metabolism and conversion to high value substances; however, they mostly are devoted to bacteria or the yeast Saccharomyces cerevisiae. This review is devoted to reviewing pentose metabolism and bioconversion mostly in non-conventional yeasts, which naturally metabolize xylose. Pentose metabolism in the recombinant strains of S. cerevisiae is also considered for comparison. The available data on ribose, xylose, L-arabinose transport, metabolism, regulation of these processes, interaction with glucose catabolism and construction of the productive strains of high-value chemicals or pentose (ribose) itself are described. In addition, genome studies of the natural xylose metabolizing yeasts and available tools for their molecular research are reviewed. Metabolism of other pentoses (2-deoxyribose, D-arabinose, lyxose) is briefly reviewed.

Bacterial staphylokinase as a promising third-generation drug in the treatment for vascular occlusion

Vascular occlusion is one of the major causes of mortality and morbidity. Blood vessel blockage can lead to thrombotic complications such as myocardial infarction, stroke, deep venous thrombosis, peripheral occlusive disease, and pulmonary embolism. Thrombolytic therapy currently aims to rectify this through the administration of recombinant tissue plasminogen activator. Research is underway to design an ideal thrombolytic drug with the lowest risk. Despite the potent clot lysis achievable using approved thrombolytic drugs such as alteplase, reteplase, streptokinase, tenecteplase, and some other fibrinolytic agents, there are some drawbacks, such as high production cost, systemic bleeding, intracranial hemorrhage, vessel re-occlusion by platelet-rich and retracted secondary clots, and non-fibrin specificity. In comparison, bacterial staphylokinase, is a new, small-size plasminogen activator, unlike bacterial streptokinase, it hinders the systemic degradation of fibrinogen and reduces the risk of severe hemorrhage. A fibrin-bound plasmin-staphylokinase complex shows high resistance to a₂-antiplasmin-related inhibition. Staphylokinase has the potential to be considered as a promising thrombolytic agent with properties of cost-effective production and the least side effects.

Advances in Using Hansenula polymorpha as Chassis for Recombinant Protein Production

The methylotrophic yeast Hansenula polymorpha, known as a non-conventional yeast, is used for the last 30 years for the production of recombinant proteins, including enzymes, vaccines, and biopharmaceuticals. Although a large number of reviews have been published elucidating the applications of this yeast as a cell factory, the latest was released about 10 years ago. Therefore, this review aimed at summarizing available information on the use of H. polymorpha as a host for recombinant protein production in the last decade. Examples of chemicals and virus-like particles produced using this yeast also are discussed. Firstly, the aspects that feature this yeast as a host for recombinant protein production are highlighted including the techniques available for its genetic manipulation as well as strategies for cultivation in bioreactors. Special attention is given to the novel genomic editing tools, mainly CRISPR/Cas9 that was recently established in this yeast. Finally, recent examples of using H. polymorpha as an expression platform are presented and discussed. The production of human Parathyroid Hormone (PTH) and Staphylokinase (SAK) in H. polymorpha are described as case studies for process establishment in this yeast. Altogether, this review is a guideline for this yeast utilization as an expression platform bringing a thorough analysis of the genetic aspects and fermentation protocols used up to date, thus encouraging the production of novel biomolecules in H. polymorpha.

Functional analysis of Mpk1-mediated cell wall integrity signaling pathway in the thermotolerant methylotrophic yeast Hansenula polymorpha

Understanding the characteristics and regulation mechanisms of cell wall integrity (CWI) in yeast is important not only for basic research but also in biotechnological applications. We found significantly different CWIs in two representative strains of the thermotolerant methylotrophic yeast Hansenula polymorpha. Compared to the A16 strain (classified as Ogataea polymorpha), the DL1-L strain (classified as Ogataea parapolymorpha) has a thinner cell wall that was found to be more fragile following long-term cultivation and more sensitive to zymolyase. To gain a deeper insight into this difference, we compared the characteristics of the Mpk1pmediated CWI signaling pathway in the two strains. While a DL1-L mutant deficient in Mpk1p (mpk1Δ) showed severe growth retardation at both normal and high growth temperatures and in the presence of cell-wall disrupting agents, the A16 mpk1Δ mutant displayed only a mild defect in cell growth. Sorbitol effect on rescuing growth retardation was different in the two mpk1Δ strains, which could partly be ascribed to subtle differences in the activation of HOG pathway. Among the cell wall disruptors evaluated, only caffeine clearly increased phosphorylation of Mpk1p in DL1-L, but not in A16. A transcriptome analysis of the DL1-L strain revealed that caffeine significantly increased the expression of a subset of cell-wall related genes in an Mpk1p-dependent manner, but not the expected Rlm1-target genes. Taken together, our data support an essential role for Mpk1p in maintaining CWI in H. polymorpha, although the requirement for Mpk1p and its regulation under diverse stress conditions varies depending on the strain background.