pyTWMR: transcriptome-wide Mendelian randomization in python.

MOTIVATION: Mendelian randomization (MR) is a widely used approach to estimate causal effect of variation in gene expression on complex traits. Among several MR-based algorithms, transcriptome-wide summary statistics-based Mendelian Randomization approach (TWMR) enables the uses of multiple SNPs as instruments and multiple gene expression traits as exposures to facilitate causal inference in observational studies. RESULTS: Here we present a Python-based implementation of TWMR and revTWMR. Our implementation offers GPU computational support for faster computations and robust computation mode resilient to highly correlated gene expressions and genetic variants. AVAILABILITY AND IMPLEMENTATION: pyTWMR is available at github.com/soreshkov/pyTWMR.

The crystal structure of yeast mitochondrial type pyrophosphatase provides a model to study pathological mutations in its human ortholog.

Mutations in human ppa2 gene encoding mitochondrial inorganic pyrophosphatase (PPA2) result in the mitochondria malfunction in heart and brain and lead to early death. In comparison with its cytosolic counterpart, PPA2 of any species is a poorly characterized enzyme with a previously unknown 3D structure. We report here the crystal structure of PPA2 from yeast Ogataea parapolymorpha (OpPPA2), as well as its biochemical characterization. OpPPA2 is a dimer, demonstrating the fold typical for other eukaryotic Family I pyrophosphatases, including the human cytosolic enzyme. Cofactor Mg2+ ions found in OpPPA2 structure have similar coordination to most known Family I pyrophosphatases. Most of the residues associated with the pathological mutations in human PPA2 are conserved in OpPPA2, and their structural context suggests possible explanations for the effects of the mutations on the human enzyme. In this work, the mutant variant of OpPPA2, Met52Val, corresponding to the natural pathogenic variant Met94Val of human PPA2, is characterized. The obtained structural and biochemical data provide a step to understanding the structural basis of PPA2-associated pathologies.

Aminooxy Click Modification of a Periodate-Oxidized Immunoglobulin G: A General Approach to Antibody-Drug Conjugates with Dye-Mediated Expeditious Stoichiometry Control.

A universal approach to the construction of antibody-drug conjugates (ADCs) has been developed. It relies on periodate oxidation of naturally present glycans of immunoglobulin G, followed by oxime ligation and, optionally, copper(I)-catalyzed alkyne-azide cycloaddition for conjugation with a toxic payload. The introduction of highly absorbing cyanine dyes into the linker allows for facile determination of the drug-antibody ratio. We applied this methodology to the synthesis of cytotoxic conjugates of an antibody against the tumor-associated antigen PRAME with doxorubicin and monomethyl auristatin E (MMAE). The resultant conjugates retained their affinity to a large extent, yet their cytotoxicity in vitro varied dramatically: while the doxorubicin-based conjugate did not produce any effect on cells, the MMAE-based one demonstrated specific activity against PRAME-expressing cancer cell lines. Importantly, the latter conjugate constitutes the first reported example of a PRAME-targeting ADC.

When less is more: sketching with minimizers in genomics.

The exponential increase in sequencing data calls for conceptual and computational advances to extract useful biological insights. One such advance, minimizers, allows for reducing the quantity of data handled while maintaining some of its key properties. We provide a basic introduction to minimizers, cover recent methodological developments, and review the diverse applications of minimizers to analyze genomic data, including de novo genome assembly, metagenomics, read alignment, read correction, and pangenomes. We also touch on alternative data sketching techniques including universal hitting sets, syncmers, or strobemers. Minimizers and their alternatives have rapidly become indispensable tools for handling vast amounts of data.

Reanalysis of mtDNA mutations of human primordial germ cells (PGCs) reveals NUMT contamination and suggests that selection in PGCs may be positive.

The resilience of the mitochondrial genome (mtDNA) to a high mutational pressure depends, in part, on negative purifying selection in the germline. A paradigm in the field has been that such selection, at least in part, takes place in primordial germ cells (PGCs). Specifically, Floros et al. (Nature Cell Biology 20: 144-51) reported an increase in the synonymity of mtDNA mutations (a sign of purifying selection) between early-stage and late-stage PGCs. We re-analyzed Floros' et al. data and determined that their mutational dataset was significantly contaminated with single nucleotide variants (SNVs) derived from a nuclear sequence of mtDNA origin (NUMT) located on chromosome 5. Contamination was caused by co-amplification of the NUMT sequence by cross-specific PCR primers. Importantly, when we removed NUMT-derived SNVs, the evidence of purifying selection was abolished. In addition to bulk PGCs, Floros et al. reported the analysis of single-cell late-stage PGCs, which were amplified with different sets of PCR primers that cannot amplify the NUMT sequence. Accordingly, there were no NUMT-derived SNVs among single PGC mutations. Interestingly, single PGC mutations show adecreaseof synonymity with increased intracellular mutant fraction. More specifically, nonsynonymous mutations show faster intracellular genetic drift towards higher mutant fraction than synonymous ones. This pattern is incompatible with predominantly negative selection. This suggests that germline selection of mtDNA mutations is a complex phenomenon and that the part of this process that takes place in PGCs may be predominantly positive. However counterintuitive, positive germline selection of detrimental mtDNA mutations has been reported previously andpotentially may be evolutionarily advantageous.