The association of glycolytic enzymes from yeast confers resistance against inhibition by trehalose

Proteomics Readjustment of the Yarrowia lipolytica Yeast in Response to Increased Temperature and Alkaline Stress

Yeasts cope with a wide range of environmental challenges using different adaptive mechanisms. They can prosper at extreme ambient pH and high temperatures; however, their adaptation mechanisms have not been entirely investigated. Previously, we showed the pivotal role and flexibility of the sugar and lipid composition of Yarrowia lipolytica W 29 upon adaptation to unfavorable conditions. In this study, we showed that extreme pH provoked significant changes in the cell wall proteins expression, with an increase in both the chaperones of heat shock protein HSP60 and some other proteins with chaperone functions. The mitochondria activity changes inducing the VDAC and malate dehydrogenase played an essential role in the adaptation, as did the altered carbohydrate metabolism, promoting its shift towards the pyruvate formation rather than gluconeogenesis. The elevated temperature led to changes in the cell wall proteins and chaperones, the induced expression of the proteins involved in the cell structural organization, ribosomal proteins, and the enzymes of formaldehyde degradation. Moreover, the readjustment of the protein composition and amount under combined stress indicated the promotion of catabolic processes related to scavenging the damaged proteins and lipids. Under all of the stress conditions studied, the process of folding, stress resistance, redox adaptation, and oxidative phosphorylation were the dominant pathways. The combined chronic alkaline and heat stress (pH 9.0, 38 °C) led to cross-adaptation, which caused "switching" over the traditional metabolism to the adaptation to the most damaging stress factor, namely the increased temperature.

Inhibition of S. aureus-Infection of HUVECs by Trehalose and Glucose-functionalized Gold Nanoparticles

Microbial adhesion to host cells represents the initial step in the infection process. Several methods have been explored to inhibit microbial adhesion including the use of glycopolymers based on mannose, galactose, sialic acid and glucose. These sugar receptors are however abundant in the body and they are not unique to bacteria. Trehalose in contrast is a unique disaccharide that is wildly expressed by microbes. This carbohydrate has not yet been explored as an anti-adhesive. Herein, gold nanoparticles (AuNPs) coated with trehalose-based polymers were prepared and compared to glucose-functionalized AuNPs and examined for their ability to prevent binding to endothelial cells. Acting as anti-adhesive, trehalose-functionalized nanoparticles decreased the binding of S. aureus to HUVEC cells, while outperforming the control nanoparticles. Microscopy revealed that trehalose coated nanoparticle bound strongly to S. aureus compared to the controls. In conclusion, nanoparticles based on trehalose could be a non-toxic alternative to inhibit S. aureus infection.

The paradoxical and still obscure properties of fungal extracellular vesicles

Early compositional studies of fungal EVs revealed a complex combination of biomolecules, including proteins, lipids, glycans, polysaccharides, nucleic acid and pigments, indicating that these compartments could be involved with multiple functions. Curiously, some of the activities attributed to fungal EVs were already attested experimentally and are implicated with contrasting effects in vitro and in vivo. For instance, the presence of virulence factors is correlated with increased pathogenic potential. Indeed, the administration to hosts of EVs along with some fungal pathogens seems to help the disease development. However, it has been clearly shown that immunization of insects and mice with fungal EVs can protect these animals against a subsequent infection. Fungal EVs not only influence the host response, as concluded from the observation that these compartments also work as messengers between fungal organisms. In this context, despite their size characterization, other physical properties of EVs are poorly known. For instance, their stability and half-life under physiological conditions can be a crucial parameter determining their long-distance effects. In this review, we will discuss the paradoxical and still unexploited functions and properties of fungal EVs that could be determinant for their biological functions.

Breaking the Fourth Wall: Modulating Quaternary Associations for Protein Regulation and Drug Discovery

Protein-protein interactions (PPIs) are an effective means to orchestrate intricate biological processes required to sustain life. Approximately 650 000 PPIs underlie the human interactome; thus underscoring its complexity and the manifold signaling outputs altered in response to changes in specific PPIs. This minireview illustrates the growing arsenal of PPI assemblies and offers insights into how these varied PPI regulatory modalities are relevant to customized drug discovery, with a focus on cancer. First, known and emerging PPIs and PPI-targeted drugs of both natural and synthetic origin are categorized. Building on these discussions, the merits of PPI-guided therapeutics over traditional drug design are discussed. Finally, a compare-and-contrast section for different PPI blockers, with gain-of-function PPI interventions, such as PROTACS, is provided.

A cryoprotectant induces conformational change in glyceraldehyde-3-phosphate dehydrogenase

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a glycolytic enzyme, catalyses the conversion of D-glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate. While mammalian and yeast GAPDHs are multifunctional proteins that have additional functions beyond those involved in glycolysis, including reactions related to nuclear RNA transport, DNA replication/repair, membrane fusion and cellular apoptosis, Escherichia coli GAPDH (ecGAPDH) has only been reported to function in glycolysis. The S-loop of GAPDH is required for interaction with its cofactor and with other proteins. In this study, the three-dimensional crystal structure of GAPDH treated with trehalose is reported at 2.0 Å resolution. Trehalose was used as a cryoprotectant for the GAPDH crystals. The structure of trehalose-bound ecGAPDH was compared with the structures of both NAD+-free and NAD+-bound ecGAPDH. At the S-loop, the bound trehalose in the GAPDH structure induces a 2.4° rotation compared with the NAD+-free ecGAPDH structure and a 3.1° rotation compared with the NAD+-bound ecGAPDH structure.

Carbon metabolism and transcriptional variation in response to salt stress in the genome shuffled Candida versatilis and a wild-type salt tolerant yeast strain

The carbon metabolism and molecular mechanisms of adaptation response when exposed to conditions causing osmotic stress in strains of a wild-type of Candida versatilis (WT) and S3–5 were investigated.

Inhibitory Role of Greatwall-Like Protein Kinase Rim15p in Alcoholic Fermentation via Upregulating the UDP-Glucose Synthesis Pathway in Saccharomyces cerevisiae

The high fermentation rate of Saccharomyces cerevisiae sake yeast strains is attributable to a loss-of-function mutation in the RIM15 gene, which encodes a Greatwall-family protein kinase that is conserved among eukaryotes. In the present study, we performed intracellular metabolic profiling analysis and revealed that deletion of the RIM15 gene in a laboratory strain impaired glucose-anabolic pathways through the synthesis of UDP-glucose (UDPG). Although Rim15p is required for the synthesis of trehalose and glycogen from UDPG upon entry of cells into the quiescent state, we found that Rim15p is also essential for the accumulation of cell wall β-glucans, which are also anabolic products of UDPG. Furthermore, the impairment of UDPG or 1,3-β-glucan synthesis contributed to an increase in the fermentation rate. Transcriptional induction of PGM2 (phosphoglucomutase) and UGP1 (UDPG pyrophosphorylase) was impaired in Rim15p-deficient cells in the early stage of fermentation. These findings demonstrate that the decreased anabolism of glucose into UDPG and 1,3-β-glucan triggered by a defect in the Rim15p-mediated upregulation of PGM2 and UGP1 redirects the glucose flux into glycolysis. Consistent with this, sake yeast strains with defective Rim15p exhibited impaired expression of PGM2 and UGP1 and decreased levels of β-glucans, trehalose, and glycogen during sake fermentation. We also identified a sake yeast-specific mutation in the glycogen synthesis-associated glycogenin gene GLG2, supporting the conclusion that the glucose-anabolic pathway is impaired in sake yeast. These findings demonstrate that downregulation of the UDPG synthesis pathway is a key mechanism accelerating alcoholic fermentation in industrially utilized S. cerevisiae sake strains.

Cyanohydrin reactions enhance glycolytic oscillations in yeast

Synchronous metabolic oscillations can be induced in yeast by addition of glucose and removal of extracellular acetaldehyde (ACAx). Compared to other means of ACAx removal, cyanide robustly induces oscillations, indicating additional cyanide reactions besides ACA to lactonitrile conversion. Here, (13)C NMR is used to confirm our previous hypothesis, that cyanide directly affects glycolytic fluxes through reaction with carbonyl-containing compounds. Intracellularly, at least 3 cyanohydrins were identified. Extracellularly, all signals could be identified and lactonitrile was found to account for ~66% of total cyanide removal. Simulations of our updated computational model show that intracellular cyanide reactions increase the amplitude of oscillations and that cyanide addition lowers [ACA] instantaneously. We conclude that cyanide provides the following means of inducing global oscillations: a) by reducing [ACAx] relative to oscillation amplitude, b) by targeting multiple intracellular carbonyl compounds during fermentation, and c) by acting as a phase resetting stimulus.

The yeast protein interaction network has a capacity for self-organization

The organization of the cellular interior gives rise to properties including metabolic channeling and micro-compartmentalization of signaling. Here, we use a lattice model of molecular crowding, together with literature-derived protein interactions and abundances, to describe the molecular organization and stoichiometry of local cellular regions, showing that physical protein-protein interactions induce emergent structures not seen when random interaction networks are modeled. Specifically, we find that the lattices give rise to micro-groups of enzymes on the surfaces of protein clusters. These arrangements of proteins are also robust to protein overexpression, while still showing evidence for expression tuning. Our results indicate that some of the complex organization of the cell may derive from simple rules of molecular aggregation and interaction.

Linking post-translational modifications and variation of phenotypic traits

Enzymes can be post-translationally modified, leading to isoforms with different properties. The phenotypic consequences of the quantitative variability of isoforms have never been studied. We used quantitative proteomics to dissect the relationships between the abundances of the enzymes and isoforms of alcoholic fermentation, metabolic traits, and growth-related traits in Saccharomyces cerevisiae. Although the enzymatic pool allocated to the fermentation proteome was constant over the culture media and the strains considered, there was variation in abundance of individual enzymes and sometimes much more of their isoforms, which suggests the existence of selective constraints on total protein abundance and trade-offs between isoforms. Variations in abundance of some isoforms were significantly associated to metabolic traits and growth-related traits. In particular, cell size and maximum population size were highly correlated to the degree of N-terminal acetylation of the alcohol dehydrogenase. The fermentation proteome was found to be shaped by human selection, through the differential targeting of a few isoforms for each food-processing origin of strains. These results highlight the importance of post-translational modifications in the diversity of metabolic and life-history traits.

Copper stress and filamentous fungus Humicola lutea 103 — ultrastructural changes and activities of key metabolic enzymes

Humicola lutea 103 is a copper-tolerant fungal strain able to grow in the presence of 300 μg·mL–1 Cu2+ under submerged cultivation. To prevent the consequences of copper overload, microorganisms have evolved molecular mechanisms that regulate its uptake, intracellular traffic, storage, and efflux. In spite of this avoidance strategy, high heavy-metal concentrations caused distinct and widespread ultrastructural alterations in H. lutea. The mitochondria were the first and main target of the toxic action. The effect of copper on activities of the key enzymes (hexokinase, glucose-6-phosphate dehydrogenase, malate dehydrogenase, and isocitrate dehydrogenase) included in the 3 main metabolic pathways, glycolysis, pentose phosphate pathway, and tricarboxylic acid cycle, was investigated. High metal concentrations exhibited a dramatic negative effect on hexokinase, while the other 3 enzymes showed a significant and dose-dependent stimulation. On the basis of the present and previous results we concluded that the copper-induced oxidative stress plays an important role in the fungal tolerance to high Cu 2+ concentrations.

Patterns of indirect protein interactions suggest a spatial organization to metabolism

It has long been believed that cells organize their cytoplasm so as to efficiently channel metabolites between sequential enzymes. This metabolic channeling has the potential to yield higher metabolic fluxes as well as better regulatory control over metabolism. One mechanism for achieving such channeling is to ensure that sequential enzymes in a pathway are physically close to each other in the cell. We present evidence that indirect protein interactions between related enzymes represent a global mechanism for achieving metabolic channeling; the intuition being that protein interactions between enzymes and non-enzymatic mediator proteins are a powerful means of physically associating enzymes in a modular fashion. By analyzing the metabolic and protein-protein interactions networks of Escherichia coli, yeast and humans, we are able to show that all three species have many more indirect protein interactions linking enzymes that share metabolites than would be expected by chance. Moreover, these interactions are distributed non-randomly in the metabolic network. Our analyses in yeast and E. coli show that reactions possessing such interactions also show higher flux than do those lacking them. On the basis of these observations, we suggest that an important role of protein interactions with mediator proteins is to contribute to the spatial organization of the cell. This hypothesis is supported by the fact that these mediator proteins are also enriched with annotations related to signal transduction, a system where scaffolding proteins are known to limit cross-talk by controlling spatial localization.