Biology subjects

von Velsen, J.

Publications and source records attributed to von Velsen, J..

6 recordsLinked to original sources

bioRxiv2026

Molecular basis of mitogen-activated protein kinase ERK2 activation by its upstream kinase MEK1

The RAS-RAF-MEK-ERK mitogen-activated protein kinase (MAPK) pathway relays extracellular signals into a cellular response and its dysregulation leads to many pathologies, particularly cancer. Here, we determined cryo-EM structures of the MAP2K MEK1 activating its substrate MAPK ERK2, the final event in the cascade. We define the molecular details of specificity and phosphoryl transfer to the tyrosine of the ERK2 activation loop and examine the mechanism of substrate recognition using solution techniques and molecular dynamics. Binding of the substrate MAPK leads to release of the MAP2K catalytic machinery, a mechanism enhanced in many gain of function disease mutations. Further, we observe that ERK2 release is not required for nucleotide exchange, suggesting how a processive mechanism could proceed. Our data advance the understanding of MAPK signalling and provide a starting point for drug development. One-Sentence SummaryCryo-EM structures of the MEK1-ERK2 complex reveal details of cellular signal transmission.

molecular biology↗

bioRxiv2025

Hydra domain drives SNF2L multimerization and marks ISWI diversification in parasites

ISWI chromatin remodelers are conserved regulators of nucleosome positioning and chromatin accessibility across eukaryotes, yet their evolutionary diversification is poorly understood. In the apicomplexan parasite Toxoplasma gondii, we identify Hydra, a previously unrecognized globular domain embedded within TgSNF2L, one of two ISWI paralogues. Hydra is structurally unique, lacking homology to any known protein fold, and represents a lineage-specific insertion in an otherwise structurally conserved protein family. Biochemical analyses reveal that the isolated Hydra domain self-assembles into stable oligomers, undergoing reversible equilibrium with its monomeric form. Cryo-electron microscopy analysis reveals discrete globular assemblies, though little consistency could be obtained, suggesting a highly dynamic complex. Deletion of Hydra from full-length TgSNF2L disrupts its intrinsic ability to form higher order oligomers in solution, yielding predominantly monomeric and dimeric species. Functionally, the Hydra-driven multimerization of TgSNF2L modulates its availability for chromatin engagement in response to cell-cycle cues. Hydra thus represents the first reported structural innovation within the ISWI family.

molecular biology↗

bioRxiv2024

Metal fluorides - multi-functional tools for the study of phosphoryl transfer enzymes

Enzymes facilitating the transfer of phosphate groups constitute the most extensive protein group across all kingdoms of life, making up approximately 10% of the proteins found in the human genome. Understanding the mechanisms by which enzymes catalyse these reactions is essential in characterising the processes they regulate. Metal fluorides can be used as multifunctional tools for the study of these enzymes. These ionic species bear the same charge as phosphate and the transferring phosphoryl group and, in addition, allow the enzyme to be trapped in catalytically important states with spectroscopically sensitive atoms interacting directly with active site residues. The ionic nature of these phosphate surrogates also allows their removal and replacement with other analogues. Here, we describe the best practices to obtain these complexes, their use in NMR, X-ray crystallography, cryoEM and SAXS and describe a new metal fluoride, scandium tetrafluoride, which has significant anomalous signal with soft X-rays. Highlights Enzymes that catalyse phosphoryl transfer are the largest family of enzymes and are involved in the storage and transmission of genetic information, energy transfer, signalling and cellular differentiation Metal fluorides form a comprehensive tool kit to study the mechanisms of these enzymes by stabilizing the active conformation; mimicking both the transition state and ground state; and placing spectroscopically sensitive atoms into the active site A guide is presented to the optimal formation of these complexes and their use in a wide variety of techniques in structural biology

molecular biology↗

bioRxiv2024

The MAP2Ks can use ADP to phosphorylate and activate their substrate MAPKs in vitro

Kinases are a diverse group of enzymes that use ATP to phosphorylate a variety of substrates. Protein kinases evolved in eukaryotes as important mediators of cell signalling that target specific amino acid side chains to modulate downstream protein function. Among them, the MAPKs (mitogen-activated protein kinases) are a family of intracellular protein kinases that form signalling cascades responding to a number of stimuli, that control fundamental mechanisms such as proliferation, differentiation, inflammation and cell death. Signals propagate through consecutive kinases which eventually phosphorylate and activate a MAPK. Here, we show that the dual specificity threonine/tyrosine MAP kinase kinases (MAP2Ks or MEKs) are able to phosphorylate and activate their substrate MAPKs using ADP as well as ATP in vitro. As the pathways are involved in the stress response, we speculate that it would represent an advantage to be able to maintain signalling under conditions such as hypoxia, that occur under a number of cell stresses, including cancer and atherosclerosis, where the available pool of ATP could be depleted.

biochemistry↗

bioRxiv2023

The structural mechanism of MCIA complex assembly links mitochondrial redox pathways

The mitochondrial Complex I assembly (MCIA) complex is an essential player in the biogenesis of respiratory Complex I (CI), the multiprotein complex responsible for the initiation of oxidative phosphorylation (OXPHOS). It is not well understood how MCIA facilitates the assembly of CI. Here we report the structural basis of the complex formation between the MCIA subunits ECSIT and ACAD9. ECSIT binding induces a major conformational change in the FAD-binding loop of ACAD9, resulting in efflux of the FAD cofactor and redeployment of ACAD9 from fatty acid {beta}-oxidation (FAO) to CI assembly. We identify an adjacent -helix as a key structural element that specifically enables the CI assembly functionality of ACAD9, distinguishing it from its closely related VLCAD counterpart. Furthermore, we show that ECSIT is phosphorylated in vitro and ex cellulo and provide evidence that phosphorylation downregulates its association with ACAD9. Interestingly, ECSIT has previously been linked to the pathogenesis of Alzheimers disease and here we show that ECSIT phosphorylation in neuronal cells is reduced upon exposure to amyloid-{beta} (A{beta}) oligomers. These findings shed light on the assembly of the MCIA complex and implicate ECSIT as a potential reprogrammer of bioenergetic metabolic pathways that can be altered when mitochondria are affected by A{beta} toxicity, a hallmark of Alzheimers disease.

molecular biology↗

bioRxiv2019

Controlled dehydration, structural flexibility, and Gadolinium MRI contrast compound binding in human plasma glycoprotein afamin

Afamin, a human blood plasma glycoprotein, a putative multi-functional transporter of hydrophobic molecules and a marker for metabolic syndrome, poses multiple challenges for crystallographic structure determination, both practically and in analysis of the models. Several hundred crystals were analysed, and unusual variability in cell volume and difficulty solving the structure despite a ~34% sequence identity with non-glycosylated human serum albumin indicated that the molecule exhibits variable and context-sensitive packing, despite greatly simplified glycosylation in insect cell expressed recombinant afamin. Controlled dehydration of the crystals was able to stabilise the orthorhombic crystal form reducing the number of molecules in the asymmetric unit from the monoclinic form and changing the conformational states of the protein. An iterative strategy, using fully automatic experiments available on MASSIF-1, was used to quickly determine the optimal protocol to achieve the phase transition that should be readily applicable to many types of sample. The study also highlights the drawback of using a single crystallographic structure model for computation modelling purposes given that conformational state of the binding sites and electron density in the binding site, likely resulting from PEGs, greatly varies between models. This also holds for the analysis of unspecific low-affinity ligands, where often a variety fragments with similar uncertainty can be modelled, inviting interpretative bias. As a promiscuous transporter, afamin also seems to bind Gadoteridol, a magnetic resonance imaging contrast compound, in at least two sites. One pair of Gadoteridol molecules is located near the human albumin Sudlow-site, and a second Gadoteridol at an intermolecular site in proximity of domain IA. The data from the co-crystals provide an opportunity to evaluate modern metrics of data quality in the context of the information that can be gleaned from data sets that would be abandoned on classical measures.\n\nSynopsisControlled dehydration experiments have revealed a new crystal form of afamin, a human blood plasma glycoprotein and transporter of hydrophobic molecules. The comparison shows substantial molecular plasticity and amplifies the necessity to examine multiple crystal forms and to refine multiple models, while at the same time the new structure cautions against interpretation of fatty acid ligand density in crystals derived from PEG as major precipitants. An isomorphic low-resolution structure model suggests that afamin is capable of transporting Gadolinium-DO3A, a magnetic resonance imaging compound.

biochemistry↗