Biology subjects

Heidebrecht, T.

Publications and source records attributed to Heidebrecht, T..

5 recordsLinked to original sources

bioRxiv2023

Distant sequence regions of JBP1 contribute to J-DNA binding

Base-J ({beta}-D-Glucopyranosyloxymethyluracil) is a modified DNA nucleotide that replaces 1% of thymine in kinetoplastid flagellates. The biosynthesis and maintenance of base-J depends on the base-J Binding Protein 1 (JBP1), that has a thymidine hydroxylase domain (THD) and a J-DNA binding domain (JDBD). How the THD synergizes with the JDBD to hydroxylate thymine in specific genomic sites, maintaining base-J during semi-conservative DNA replication, remains unclear. Here we present a crystal structure of the JDBD including a previously disordered DNA-contacting loop and use it as starting point for Molecular Dynamics (MD) simulations and computational docking studies to propose recognition models for JDBD binding to J-DNA. These models guided mutagenesis experiments, providing additional data for docking, which reveals a binding mode for JDBD onto J-DNA. This model, together with the crystallographic structure of the TET2 JBP1-homologue in complex with DNA and the AlphaFold model of full-length JBP1, allowed us to hypothesize that the flexible JBP1 N-terminus contributes to DNA-binding, which we confirmed experimentally. A high-resolution JBP1:J-DNA complex, which must involve conformational changes, would however need to be determined experimentally to further understand this unique underlying molecular mechanism that ensures replication of epigenetic information.

biochemistry↗

bioRxiv2018

The domain architecture of JBP1 suggests synergy between J-base DNA binding and thymidine hydroxylase activity

JBP1 (J-DNA Binding Protein 1) contributes to biosynthesis and maintenance of base J ({beta}-D-glucosyl-hydroxymethyluracil), a modification of thymidine (T) confined to pathogenic protozoa. JBP1 has two known functional domains: an N-terminal thymidine hydroxylase (TH) homologous to the 5-methylcytosine hydroxylase domain in TET proteins; and a J-DNA binding domain (JDBD) that resides in the middle of JBP1. Here we show that removing JDBD from JBP1 results in a soluble protein ({Delta}-JDBD) with the N- and C-terminal regions tightly associated together in a well-ordered domain. This {Delta}-JDBD domain retains thymidine hydroxylation activity in vitro, but displays a fifteen-fold lower apparent rate of hydroxylation compared to JBP1. Small Angle X-ray Scattering (SAXS) experiments on JBP1 and JDBD in the presence and absence of J-DNA, and on {Delta}-JDBD, allowed us to generate low-resolution three-dimensional models. We conclude that {Delta}-JDBD, and not the N-terminal region of JBP1 alone, is a distinct folding unit. Our SAXS-based model supports the notion that binding of JDBD specifically to J-DNA can facilitate hydroxylation a T 12-14 bp downstream on the complementary strand of the J-recognition site. We postulate that insertion of the JDBD module in the {Delta}-JDBD scaffold during evolution provided a mechanism to synergize between J recognition and T hydroxylation, ensuring inheritance of J in specific sequence patterns following DNA replication.

biochemistry↗

bioRxiv2018

Direct binding of Cdt2 to PCNA is important for targeting the CRL4Cdt2 E3 ligase activity to Cdt1

The CRL4Cdt2 ubiquitin ligase complex is an essential regulator of cell-cycle progression and genome stability, ubiquitinating substrates such as p21, Set8 and Cdt1, via a display of substrate degrons on PCNA. Here, we examine the hierarchy of the ligase and substrate recruitment kinetics onto PCNA at sites of DNA replication. We demonstrate that the C-terminal end of Cdt2 bears a PCNA interaction protein motif (PIP box, Cdt2PIP), which is necessary and sufficient for binding of Cdt2 to PCNA. Cdt2PIP binds PCNA directly with high affinity, two orders of magnitude tighter than the PIP box of Cdt1. X-ray crystallographic structures of PCNA bound to Cdt2PIP and Cdt1PIP show that the peptides occupy all three binding sites of the trimeric PCNA ring. Mutating Cdt2PIP weakens the interaction with PCNA, rendering CRL4Cdt2 less effective in Cdt1 ubiquitination and leading to defects in Cdt1 degradation. The molecular mechanism we present suggests a new paradigm for bringing substrates to the CRL4-type ligase, where the substrate receptor and substrates bind to a common multivalent docking platform to enable subsequent ubiquitination.\n\nSummary blurbThe C-terminal end of Cdt2 contains a PIP-box for binding to PCNA to promote CRL4Cdt2 function, creating a new paradigm, where the substrate receptor and substrates bind to a common multivalent docking platform for ubiquitination.

molecular biology↗

bioRxiv2018

Lysophosphatidic acid produced by Autotaxin acts as an allosteric modulator of its catalytic efficiency

Autotaxin is a secreted phosphodiesterase that converts lysophosphatidylcholine (LPC) into lysophosphatidic acid (LPA). LPA controls key cellular responses such as migration, proliferation and survival, implicating ATX-LPA signalling in various (patho)physiological processes and establishing it as a drug target. ATX structural and functional studies have revealed an orthosteric and an allosteric site, the \"pocket\" and the \"tunnel\". Here, we revisit the kinetics of the ATX catalytic cycle in light of allosteric regulation, dissecting the different steps and pathways that lead to LPC hydrolysis. Consolidating all experimental kinetics data to a comprehensive catalytic model supported by molecular modelling simulations, suggests a positive feedback mechanism, regulated by the abundance of the LPA products activating hydrolysis of different LPC species. Our results complement and extend current understanding of ATX hydrolysis in light of the allosteric regulation by produced LPA species, and have implications for the design and application of orthosteric and allosteric ATX inhibitors.

biochemistry↗

bioRxiv2018

Characterisation and structure determination of a llama-derived nanobody targeting the J-base binding protein 1

The J-base Binding Protein 1 (JBP1) contributes to biosynthesis and maintenance of base J ({beta}-D-glucosyl-hydroxymethyluracil), a modification of thymidine confined to some protozoa. Camelid (llama) single domain antibody fragments (nanobodies) targeting JBP1 were produced for use as crystallization chaperones. Surface plasmon resonance (SPR) screening identified Nb6 as a strong binder, recognising JBP1 with a 1:1 stoichiometry and high affinity (kD=30nM). Crystallisation trials of JBP1 in complex with Nb6, yielded crystals diffracting to 1.47[A] resolution.\n\nHowever, the asymmetric unit dimensions and molecular replacement with a nanobody structure, clearly showed that the crystals of the expected complex with JBP1 were of the nanobody alone. Nb6 crystallizes in spacegroup P31 with two molecules in the asymmetric unit; its crystal structure was refined to a final resolution of 1.64[A]. Ensemble refinement suggests that on the ligand-free state one of the complementarity determining regions (CDRs) is flexible while the other two adopt well-defined conformations.\n\nSynopsisA camelid single domain antibody fragment (nanobody) is shown to have high affinity towards its recognition target, the J-base binding protein 1 (JBP1). The serendipitous crystallisation of this nanobody alone, and its crystal structure solution and refinement to 1.64[A] resolution are described. Ensemble refinement suggests that on the ligand-free state one of the complementarity determining regions (CDRs) is flexible while the other two adopt well-defined conformations.

biochemistry↗