New aspects of formation of 1,2-cyclic phosphates by phospholipase C-delta1

Phosphoinositide-specific phospholipase C-delta1 (PI-PLC-delta1) cleaves phosphatidylinositol 4,5-bisphosphate (PI-4,5-P(2), 1), 5-phosphate (PI-5-P, 2) and 4-phosphate (PI-4-P, 3) to form the mixture of the corresponding 4,5-, 5- and 4-phosphorylated inositol 1,2-cyclic phosphate (IcP) and 1-phosphate (IP) (4-6 and 7-9, respectively). In this work, we have studied the rates of the cleavage and the ratios of the cyclic-to-acyclic phosphate products under various pH and Ca(2+) concentration conditions using 31P NMR to monitor the reactions. In agreement with the previous report (Kim et al. Biochim. Biophys. Acta 1989, 163, 177), our results indicate that the IcP/IP ratios strongly depend on the reaction conditions, with the cyclic phosphate products formed predominantly at low pH (pH 5.0) and high calcium concentration (5 mM). Surprisingly, however, we have found that at pH 8.0 and 5 mM Ca(2+), PI-5-P rather than PI-4,5-P(2) is the most preferred substrate with the highest V(max). The cleavage of PI-5-P generated also more cyclic phosphate product than the other two substrates. In addition, we have studied the analogous reaction of phosphorothioate analogues of 1 with the sulfur placed in the nonbridging (10) or bridging (13) positions. We have found that the phosphorothioate analogue 10 produced exclusively the cyclic product 11, whereas the analogue 13 afforded exlusively the acyclic product 7. These results are discussed in terms of the mechanism of PI-PLC, where the cyclic product is formed by 'leaking' from the active site before its subsequent hydrolysis. The potential significance of the cyclic products in the signaling pathways is also discussed.     

Structural aspects of Ca2+ binding by acyclic peptides: low-energy conformational domains and molecular dynamics of N-acetyl-L-prolyl-D-alanyl-L-alanine-N'-methylamide.

We have applied random-search, energy minimization and molecular dynamics simulations to investigate the structural aspects of the interaction of N-acetyl-L-prolyl-D-alanyl-L-alanine-N'-methylamide with Ca2+. Spectral data on related peptides had suggested that the beta-turn conformation might be a prerequisite for the binding of cation ion by such short linear peptides. In order to relate the conformational characteristics with the Ca(2+)-binding affinities of these peptides, the molecular events involved in cation binding need to be understood. We have addressed this problem in this study by using a systematic approach that involved the following steps. First, a random search technique was used to generate a large population of conformers for the free peptide in the absence of Ca2+. Next, the energies of these conformers were computed. Conformations with energies within 4 kcal/mol of the global minimum were analysed and found to fall into four main groups characterized by the presence of different types of hydrogen-bonded structures including single and consecutive beta-turns. The energies for interconversion of conformers from one group to another were computed and found to be relatively small (< 10 kcal/mol). Finally, molecular dynamics of the peptide at 300K in the presence of Ca2+ were used to simulate the cation binding process. Starting points for these simulations were generated by placing the ion in the vicinity of two molecules of the peptide. The simulation results showed that the conformers with two consecutive beta-turns led to the formation of a stable 2:1 (peptide:Ca2+) sandwich complex in agreement with earlier experimental observations on similar linear peptides. While the starting conformation of the peptide in the consecutive beta-turn structure allowed for the proper orientation of three carbonyl oxygen atoms for chelation to the metal ion, the dynamics of complex formation rearranged the peptide structure substantially, leading to the formation of an 8-coordinated Ca2+ complex in a dodecahedral spatial arrangement. Thus, based on the energetics of the structures and processes involved, the present study demonstrates that: a) peptide-Ca2+ complex formation is initiated by conformers adopting consecutive beta-turn structures which subsequently go over to a significantly different conformation found in the complex; and, b) The facile interconversion between the low-energy conformers in the different groups would help shift the equilibrium population towards the consecutive beta-turn structure during the complex formation.     

The story of science: successes,failures, luck,privilege, and bias

I am incredibly honored to receive the 2021 WICB Junior Award for Excellence in Research in WICB’s golden jubilee year. In this essay, I traverse my scientific journey starting with my PhD, highlighting the highs and the lows and how these intersect with luck, privilege, and bias.

V. AnanthanarayananMy pursuit for a PhD started with a hiccup—I had applied to several places in the United States, but barely got any offers due to the economic upheaval that happened that year (2008). I had to forgo any dreams of a PhD in the United States and remained in Bangalore, India to complete a project I had started with William (Bill) Thies at Microsoft Research India on a programming language for expressing biology protocols. Applying to U.S. schools was an expensive task, one which I was unwilling to put my family through again. So, a year later, when I recommenced my search for a PhD position, I set my sights on Europe. I had heard about the PhD program at the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG ) at Dresden from a friend who had just joined the institute for her PhD. Fortunately, I received an interview call from MPI-CBG. At the end of a crucial interview week at Dresden, I “matched” with Iva Tolic´’s (now Institut Ruđer Boškovic´, Croatia) lab for my PhD. At the start of my PhD, I knew next to nothing about the cytoskeleton, motor proteins, or microscopy, but I found Iva and my lab members to be some of the warmest and most welcoming people. I made friends for life and graduated with a PhD in Biophysics, with a thesis focused on understanding the regulation of the motor protein cytoplasmic dynein. I was lucky to have been able to get a position at MPI-CBG and join Iva’s lab—of the other three places in Europe I had applied to for a PhD, only one other institute invited me for an interview, which also proved to be unsuccessful.On completing my PhD in 2014, I didn’t quite know what I wanted to do. Due to personal reasons, I had to return to India and was open to options in both industry and academia. But with my training in motor protein and cytoskeleton research, I had some ideas for exploring scientific questions related to dynein activation. However, most labs I approached for a postdoctoral position were not open to a project that was outside the realm of their research focus. Nonetheless, Iva, Nenad Pavin (University of Zagreb), and Jonathon (Joe) Howard (Yale University), who were members of my thesis advisory committee, gave me the courage to continue in academia. In my naïveté, I went ahead and applied for the INSPIRE Faculty Fellowship, which is targeted at fresh PhDs and junior postdoctoral fellows to establish their own independent group at an Indian institute. To my surprise, I ended up getting the fellowship. The next issue was finding a host institute that was preferably in Bangalore, where my partner was based. I applied at a few different places, but only after I attended IndiaBioscience’s Young Investigator Meeting in 2014 did I get the chance to meet representatives of potential host institutes, including the Indian Institute of Science (IISc). After a couple of research seminars at IISc, my application was assessed and I was offered the position of INSPIRE Faculty Fellow at the newly formed Centre for BioSystems Science and Engineering, IISc.While I did not have any additional start-up funding, I was given the infrastructure and the independence to pursue my research program. It was slow and frustrating at the start, not unlike most starting labs. I always wondered if it might have been easier if I had had a regular postdoctoral stint. During this time, I also started recognizing how hard it was to be a woman in Indian academia. As a woman principal investigator, one’s authority, expertise, and ability are constantly called into question. Justifying your presence in academia on a daily basis is an exhausting task. I had a great mentor in Sandhya Visweswariah (IISc) who helped me navigate the system. I also had an extremely supportive partner, who kept me going through some of the worst times. Eventually, my lab and I landed on our feet (more about this in “My INSPIRE’d Journey”). Our research has been recognized with grants and awards, but one of the most rewarding parts of the job is seeing other lab members discovering the joy of science (I wrote about my approach to mentorship recently [https://www.nature.com/articles/s41580-020-0256-6]).Three years into the faculty fellowship, I was able to transition to an Assistant Professor position in the same institute. However, this did not change my experience as a young woman in Indian science, and the implicit and explicit biases continued. In 2020, I accepted a fantastic opportunity to further my lab’s science as an EMBL Australia Group Leader at the Single Molecule Science Node at UNSW Sydney and made the move during a pandemic. My lab’s research focus is in understanding how stochastic and rare events pertaining to cytoskeleton and motor proteins give rise to complexity in intracellular organization. With this theme as the essence of our research, we ask specific questions about motor protein regulation to effect differential cellular trafficking, mitochondria-microtubule interactions, and their role in mitochondrial dynamics, and we aim to determine barcodes of global organelle positioning in health and disease.I have the privilege of being able-bodied, born in an upper middle-class family to college-educated parents who were extremely supportive of my choices. I have also inordinately benefitted from the fact that I was born to an Indian ‘upper caste’ family. I therefore had an undue head start in life. These were circumstances beyond my control and yet played a huge role in how my story turned out. I was embarrassingly ignorant of the rampant misogyny in academia until I had to contend with explicit and implicit gender-based biases myself when I started my independent research group in India. Women make up ∼40% of science PhDs awarded in India but represent only ∼13% of Indian academia (biaswatchindia.com), highlighting the stark gender biases at play in creating a leaky pipeline. While I tried my best to voice my discontent and affect changes to create an equitable environment within my department and institute, it was slow work. In 2020, when the pandemic hit and all conferences and meetings went virtual, conference posters advertised on social media made it immediately apparent just how much women were underrepresented in Indian STEM conferences. So, I teamed up with Shruti Muralidhar (now a scientist at Deep Genomics, Canada) to found BiasWatchIndia, an initiative to document women representation and combat gender-biased panels in Indian STEM conferences.BiasWatchIndia has been in existence for a little over a year now—we have achieved several milestones, but there’s still so much to do. “Manels” (conferences that feature only men) are still as rampant as they were when we first started—40% of all Indian STEM conferences are manels. And while we have just about started to tackle the underrepresentation of women in Indian STEM, we are conscious of the intersectionality of bias with gender, caste, ableism, and socioeconomic background and aim to understand how best we can advocate for all minorities.People who are in power in academia and who oppose equity, diversity, and inclusion initiatives and instead preach merit and equality as the gold standard need to introspect, because when options and opportunities are offered without consideration to the millennia of oppression based on gender, race, and background, it is not promoting equality but upholding values that will continue to oppress underrepresented groups. Still, I am optimistic and hope to see real changes that will result in equity in academia in my lifetime.     

Helix, sheet, and polyproline II frequencies and strong nearest neighbor effects in a restricted coil library

A central issue in protein folding is the degree to which each residue's backbone conformational preferences stabilize the native state. We have studied the conformational preferences of each amino acid when the amino acid is not constrained to be in a regular secondary structure. In this large but highly restricted coil library, the backbone preferentially adopts dihedral angles consistent with the polyproline II conformation rather than alpha or beta conformations. The preference for the polyproline II conformation is independent of the degree of solvation. In conjunction with a new masking procedure, the frequencies in our coil library accurately recapitulate both helix and sheet frequencies for the amino acids in structured regions, as well as polyproline II propensities. Therefore, structural propensities for alpha-helices and beta-sheets and for polyproline II conformations in unfolded peptides can be rationalized solely by local effects. In addition, these propensities are often strongly affected by both the chemical nature and the conformation of neighboring residues, contrary to the Flory isolated residue hypothesis.     

Vacuum ultraviolet circular dichroism spectrum of beta-turn in solution.

The vacuum ultraviolet circular dichroism spectrum of an isolated 4 → 1 hydrogen bonded β-turn is reported. The observed spectrum of N-acetyl-Pro-Gly-Leu-OH at ? 40°C in trifluoroethanol is in good agreement with the theoretically calculated CD spectrum of the β-turn conformation. This spectrum, particularly the presence of a strong negative band around 180 nm and a large ratio $\text{[θ]}{}_{201}\text{[θ]}{}_{225}$, can be taken as a characteristic feature of the isolated β-turn conformation. These CD spectral features can thus be used to distinguish the β-turn conformation from the β-structure in solution.     

Recognition of Human Erythrocyte Receptors by the Tryptophan-Rich Antigens of Monkey Malaria Parasite Plasmodium knowlesi

Background

The monkey malaria parasite Plasmodium knowlesi also infect humans. There is a lack of information on the molecular mechanisms that take place between this simian parasite and its heterologous human host erythrocytes leading to this zoonotic disease. Therefore, we investigated here the binding ability of P. knowlesi tryptophan-rich antigens (PkTRAgs) to the human erythrocytes and sharing of the erythrocyte receptors between them as well as with other commonly occurring human malaria parasites.

Methods

Six PkTRAgs were cloned and expressed in E.coli as well as in mammalian CHO-K1 cell to determine their human erythrocyte binding activity by cell-ELISA, and in-vitro rosetting assay, respectively.

Results

Three of six PkTRAgs (PkTRAg38.3, PkTRAg40.1, and PkTRAg67.1) showed binding to human erythrocytes. Two of them (PkTRAg40.1 and PkTRAg38.3) showed cross-competition with each other as well as with the previously described P.vivax tryptophan-rich antigens (PvTRAgs) for human erythrocyte receptors. However, the third protein (PkTRAg67.1) utilized the additional but different human erythrocyte receptor(s) as it did not cross-compete for erythrocyte binding with either of these two PkTRAgs as well as with any of the PvTRAgs. These three PkTRAgs also inhibited the P.falciparum parasite growth in in-vitro culture, further indicating the sharing of human erythrocyte receptors by these parasite species and the biological significance of this receptor-ligand interaction between heterologous host and simian parasite.

Conclusions

Recognition and sharing of human erythrocyte receptor(s) by PkTRAgs with human parasite ligands could be part of the strategy adopted by the monkey malaria parasite to establish inside the heterologous human host.     

Proteomic Analysis of Anti-Cancerous Scopularide Production by a Marine Microascus brevicaulis Strain and Its UV Mutant

The marine fungus Microascus brevicaulis strain LF580 is a non-model secondary metabolite producer with high yields of the two secondary metabolites scopularides A and B, which exhibit distinct activities against tumour cell lines. A mutant strain was obtained using UV mutagenesis, showing faster growth and differences in pellet formation besides higher production levels. Here, we show the first proteome study of a marine fungus. Comparative proteomics were applied to gain deeper understanding of the regulation of production and of the physiology of the wild type strain and its mutant. For this purpose, an optimised protein extraction protocol was established. In total, 4759 proteins were identified. The central metabolic pathway of strain LF580 was mapped using the KEGG pathway analysis and GO annotation. Employing iTRAQ labelling, 318 proteins were shown to be significantly regulated in the mutant strain: 189 were down- and 129 upregulated. Proteomics are a powerful tool for the understanding of regulatory aspects: The differences on proteome level could be attributed to limited nutrient availability in the wild type strain due to a strong pellet formation. This information can be applied for optimisation on strain and process level. The linkage between nutrient limitation and pellet formation in the non-model fungus M. brevicaulis is in consensus with the knowledge on model organisms like Aspergillus niger and Penicillium chrysogenum.     

Stability Performance of Inductively Coupled Plasma Mass Spectrometry-Phenotyped Kernel Minerals Concentration and Grain Yield in Maize in Different Agro-Climatic Zones

Deficiency of iron and zinc causes micronutrient malnutrition or hidden hunger, which severely affects ~25% of global population. Genetic biofortification of maize has emerged as cost effective and sustainable approach in addressing malnourishment of iron and zinc deficiency. Therefore, understanding the genetic variation and stability of kernel micronutrients and grain yield of the maize inbreds is a prerequisite in breeding micronutrient-rich high yielding hybrids to alleviate micronutrient malnutrition. We report here, the genetic variability and stability of the kernel micronutrients concentration and grain yield in a set of 50 maize inbred panel selected from the national and the international centres that were raised at six different maize growing regions of India. Phenotyping of kernels using inductively coupled plasma mass spectrometry (ICP-MS) revealed considerable variability for kernel minerals concentration (iron: 18.88 to 47.65 mg kg^–1; zinc: 5.41 to 30.85 mg kg^–1; manganese: 3.30 to17.73 mg kg^–1; copper: 0.53 to 5.48 mg kg^–1) and grain yield (826.6 to 5413 kg ha^–1). Significant positive correlation was observed between kernel iron and zinc within (r = 0.37 to r = 0.52, p < 0.05) and across locations (r = 0.44, p < 0.01). Variance components of the additive main effects and multiplicative interactions (AMMI) model showed significant genotype and genotype × environment interaction for kernel minerals concentration and grain yield. Most of the variation was contributed by genotype main effect for kernel iron (39.6%), manganese (41.34%) and copper (41.12%), and environment main effects for both kernel zinc (40.5%) and grain yield (37.0%). Genotype main effect plus genotype-by-environment interaction (GGE) biplot identified several mega environments for kernel minerals and grain yield. Comparison of stability parameters revealed AMMI stability value (ASV) as the better representative of the AMMI stability parameters. Dynamic stability parameter GGE distance (GGED) showed strong and positive correlation with both mean kernel concentrations and grain yield. Inbreds (CM-501, SKV-775, HUZM-185) identified from the present investigation will be useful in developing micronutrient-rich as well as stable maize hybrids without compromising grain yield.     

PON-P2: Prediction Method for Fast and Reliable Identification of Harmful Variants

More reliable and faster prediction methods are needed to interpret enormous amounts of data generated by sequencing and genome projects. We have developed a new computational tool, PON-P2, for classification of amino acid substitutions in human proteins. The method is a machine learning-based classifier and groups the variants into pathogenic, neutral and unknown classes, on the basis of random forest probability score. PON-P2 is trained using pathogenic and neutral variants obtained from VariBench, a database for benchmark variation datasets. PON-P2 utilizes information about evolutionary conservation of sequences, physical and biochemical properties of amino acids, GO annotations and if available, functional annotations of variation sites. Extensive feature selection was performed to identify 8 informative features among altogether 622 features. PON-P2 consistently showed superior performance in comparison to existing state-of-the-art tools. In 10-fold cross-validation test, its accuracy and MCC are 0.90 and 0.80, respectively, and in the independent test, they are 0.86 and 0.71, respectively. The coverage of PON-P2 is 61.7% in the 10-fold cross-validation and 62.1% in the test dataset. PON-P2 is a powerful tool for screening harmful variants and for ranking and prioritizing experimental characterization. It is very fast making it capable of analyzing large variant datasets. PON-P2 is freely available at http://structure.bmc.lu.se/PON-P2/.