Molecular interaction of neutral trehalase with other enzymes of trehalose metabolism in the fission yeast Schizosaccharomyces pombe

Active Learning: A Shift from Passive Learning to Student Engagement Improves Understanding and Contextualization of Nutrition and Community Health

Challenging the notion of “teaching by telling,” active learning utilizes a student-oriented approach by emphasizing the concept of knowledge retention through peer interaction. To further examine the potential of active learning, we created a workshop based on didactic education and student collaboration. Participants included undergraduate students from traditionally underrepresented and disadvantaged backgrounds. The workshop was part of our summer academic enrichment program run in an urban, medically underserved community. The workshop focused on clinical and biochemical nutrition, wherein students synthesized information by discussing dietary choices and the socioeconomic aspects of nutrition. Student reception of the workshop was adjudged by anonymous surveys. The survey questions were designed to gauge how the workshop objectives were achieved. Cronbach alpha (0.276) confirmed that there was more than a single theme contained in the questions. The majority of students (97%) agreed that the workshop met the learning objectives: (1) acquire basic clinical knowledge, (2) gain a better understanding of nutrition, (3) formulate a linkage between clinical nutrition and disease, and (4) benefit from peer interaction. Students’ performance in the post-quiz (100% correct answers) had improved significantly compared to the pre-quiz (25% correct answers) suggesting acquisition, understanding and application of nutrition aspects taught in the workshop. Overall, the present study demonstrated the engagement and understanding of students with respect to learning about nutrition and community health in an active learning setting. These types of active-learning-based sessions may have broad applicability for any academic discipline to improve student engagement and knowledge retention.

Loss of ppr3, ppr4, ppr6, or ppr10 perturbs iron homeostasis and leads to apoptotic cell death in Schizosaccharomyces pombe

Pentatricopeptide repeat (PPR) proteins characterized by tandem arrays of a degenerate 35-amino-acid repeat belong to a large family of RNA-binding proteins that are involved in post-transcriptional control of organelle gene expression. PPR proteins are ubiquitous in eukaryotes, and particularly prevalent in higher plants. Schizosaccharomyces pombe has 10 PPR proteins. Among them, ppr3, ppr4, ppr6, and ppr10 participate in mitochondrial post-transcriptional processes and are required for mitochondrial electron transport chain (ETC) function. In the present work, we showed that deletion of ppr3, ppr4, ppr6, or ppr10 led to apoptotic cell death, as revealed by DAPI and Annexin V-FITC staining. These mutants also exhibited elevated levels of reactive oxygen species (ROS). RNA sequencing (RNA-seq) and quantitative RT-PCR analyses revealed that deletion of ppr10 affected critical biological processes. In particular, a core set of genes involved in iron uptake and/or iron homeostasis was elevated in the Δppr10 mutant, suggesting an elevated level of intracellular iron in the mutant. Consistent with this notion, Δppr3, Δppr4, Δppr6, and Δppr10 mutants exhibited increased sensitivity to iron. Furthermore, the iron chelator, bathophenanthroline disulfonic acid, but not the calcium chelator EGTA, nearly restored the viabilities of Δppr3, Δppr4, Δppr6, and Δppr10 mutants, and reduced ROS levels in the mutants. These results show for the first time that deletion of a ppr gene leads to perturbation of iron homeostasis. Our results also suggest that disrupted iron homeostasis in Δppr3, Δppr4, Δppr6, and Δppr10 mutants may lead to an increase in the level of ROS and induction of apoptotic cell death in S. pombe.

DATABASE

The RNA-seq data have been deposited in the National Center for Biotechnology Information (NCBI) BioProject database (accession number SRP091623) and Gene Expression Omnibus (GEO) database (accession number GSE90144).

Functional characterization of Schizosaccharomyces pombe neutral trehalase altered in phosphorylatable serine residues

The activation of neutral trehalase (Ntp1) by metabolic and physical stresses in Schizosaccharomyces pombe is dependent on protein kinases Pka1 or Sck1. Mutant ntp1 alleles altered for potentially phosphorylatable serine residues within the regulatory domain of the enzyme were integrated under the control of the native promoter in an ntp1-deleted background. The trehalase variants were expressed to a level similar to that of wild type trehalase from control cells. Wild type trehalase protein accumulated and became activated upon stress while a single change in the evolutionary conserved perfect consensus site for Pka1-dependent phosphorylation (Ser71), as well as point mutations in two other putative phosphorylation sites (Ser6, Ser51), produced inactive trehalases unresponsive to stress. Trehalose content in the trehalase mutated strains increased upon salt stress to a level comparable to that shown by an ntp1-deleted mutant. When exposed to heat shock, trehalose hyperaccumulated in the ntp1-null strain lacking trehalase protein and this phenotype was shown by some (Ser71), but not all, strains with serine mutated trehalases. The mutant trehalases retained the ability to form complexes with trehalose-6-phosphate synthase. These data support a role of potentially phosphorylated specific sites for the activation of S. pombe neutral trehalase and for the heat shock-induced accumulation of trehalose.

A role for calcium in the regulation of neutral trehalase activity in the fission yeast Schizosaccharomyces pombe

Neutral trehalases mobilize trehalose accumulated by fungal cells as a protective and storage carbohydrate. A structural feature of these enzymes is the presence of an EF-like motif similar to that shown by many Ca2+-binding proteins. In this study we provide direct evidence for physical binding of Ca2+ to neutral trehalase (Ntp1p) of the fission yeast Schizosaccharomyces pombe, and show that aspartic residues at positions 97 and 108 in the conserved putative Ca2+-binding motif of Ntp1p appear to be responsible for this interaction. Mutations in these residues do not interfere with the ability of Ntp1p to associate in vivo with trehalose-6-phosphate synthase, but prevent activation of neutral trehalase triggered by the addition of glucose or by subjecting cells to stressing conditions. Strains expressing Ntp1p variants that are unable to bind Ca2+ partially resemble those devoid of the ntp1+ gene in terms of trehalose hyperaccumulation. Gel filtration of cell extracts from wild-type cells after EDTA treatment or from cells containing Ntp1p with mutations in aspartic acid residues within the Ca2+-binding site revealed that Ntp1p eluted mainly in an inactive conformation instead of the dimeric or trimeric active form of the enzyme. These results suggest that activation of S. pombe Ntp1p under different conditions depends upon Ca2+ binding through the Ca2+-binding motif as a prerequisite for correct enzyme oligomerization to its active form. Given the high degree of conservation of the Ca2+ accommodation site, this might be a general mechanism regulating neutral trehalase activity in other yeasts and filamentous fungi.