Biology subjects
Publications and source records attributed to Jessen, H..
We present an amplicon-based assay for MinION Nanopore sequencing of monkeypox virus genomes from clinical specimens, obtaining high-quality results for up to 99 % of the genomes, even for samples with high Ct values of up to 30 which are not suitable for shotgun sequencing.
S-Adenosylmethionine (SAM) is an enzyme cofactor involved in methylation, aminopropyl transfer, and radical reactions. This versatility renders SAM-dependent enzymes of great interest in biocatalysis. The usage of SAM analogues adds to this diversity. However, high cost and instability of the cofactor impedes the investigation and usage of these enzymes. While SAM regeneration protocols from the methyltransferase (MT) byproduct S-adenosylhomocysteine are available, aminopropyl transferases and radical SAM enzymes are not covered. Here, we report an efficient one-pot system to supply or regenerate SAM and SAM analogues for all three enzyme classes. The systems flexibility is showcased by the transfer of an ethyl group with a cobalamin-dependent radical SAM MT using S-adenosylethionine as a cofactor. This shows the potential of SAM (analogue) supply and regeneration for the application of diverse chemistry, as well as for mechanistic studies using cofactor analogues.
Technical challenges have to date prevented a complete profiling of the levels of myo-inositol phosphates (InsPs) and pyrophosphates (PP-InsPs) in mammalian tissues. Here, we have deployed capillary electrophoresis mass spectrometry to identify and record the levels of InsPs and PP-InsPs in several tissues obtained from wild type mice and a newly-created PPIP5K2 knockout strain. We observe that the mouse colon harbours unusually high levels of InsPs and PP-InsPs. Additionally, the PP-InsP profile is considerably more complex than previously reported for animal cells: using chemically synthesized internal stable isotope references, and high-resolution mass spectra, we characterize two new PP-InsP isomers as 4/6-PP-InsP5 and 2-PP-InsP5. The latter has not previously been described in Nature. Analysis of feces and the commercial mouse diet suggest the latter is one potential source of noncanonical isomers in the colon. However, we also identify both molecules in the heart, indicating unknown synthesis pathways in mammals. We also demonstrate that the CE-MS method is sensitive enough to measure PP-InsPs from patient samples such as colon biopsies and peripheral blood mononuclear cells (PBMCs). Strikingly, PBMCs also contain 4/6-PP-InsP5 and 2-PP-InsP5. In summary, our study substantially expands PP-InsP biology in mammals.
The water-soluble inositol phosphates (InsPs) represent a functionally diverse group of small-molecule messengers central to a myriad of cellular processes. However, we have an incomplete understanding of InsP metabolism because the available analytical toolset for inositol phosphates is rather limited. Here, we have synthesized and utilized fully and unsymmetrically 13C-labeled myo-inositol and inositol phosphates. These probes were applied in combination with nuclear magnetic resonance spectroscopy (NMR) and capillary electrophoresis mass spectrometry (CE-MS) to further annotate central aspects of InsP metabolism in human cells. The labeling strategy provided detailed structural information via NMR - down to individual enantiomers - which overcomes a crucial blind spot in the analysis of InsPs. We uncovered a novel branch of InsP dephosphorylation in human cells which is dependent on MINPP1, a phytase-like enzyme, that contributes to cellular homeostasis. Full characterization of MINPP1 activity in vitro and in cells, provided a clear picture of this multifunctional phosphatase. Metabolic labeling with stable isotopomers thus constitutes a powerful tool for investigating InsP networks in a variety of different biological contexts.