Biology subjects

Kajander, T.

Publications and source records attributed to Kajander, T..

6 recordsLinked to original sources

bioRxiv2026

Structure determination and dual targeting of a plant TACO1 identifies its ancient role as an organelle translation regulator

Ribosome stalling caused by polyproline (PPs) motifs is common. Their translation is enhanced by accessory proteins such as YebC in bacteria, whose homolog, TRANSLATIONAL ACTIVATOR OF CYTOCHROME C OXIDASE 1 (TACO1), aids the translation of mitochondria-encoded proteins. The prevalence of PP motifs across plastid-encoded genes and their impact on the translation of photosynthesis-relevant proteins remains unexplored. Equally, a translation-enhancer of PP motifs equivalent to TACO1 for plastid ribosomes has not been reported. Here, we show that plastid genomes encode 24 proteins with a minimum of one PP motif on average, half of which are conserved in their cyanobacterial homologs, and that the vast majority of eukaryotes, including plants, encode a single TACO1 that we demonstrate to be dually targeted to mitochondria and plastids of Marchantia polymorpha. We resolved the MpTACO1 structure at 2.34 [A] by X-ray crystallography and the flexibility by small-angle X-ray scattering. Through modelling, we demonstrate that MpTACO1 can fit into the peptidyl transfer centre of plant chlororibosomes in a similar manner as human TACO1 in the mitoribosome. The identification and structure determination of the first plastid-targeted YebC/TACO1 allows us to sketch a unified model for the function and evolution of this ancient family of ribosomal accessory proteins, underscoring their indispensable role in the translation of bioenergetic membrane proteins reaching back almost 4 billion years. HighlightsO_LIDozens of GC-rich polyproline (PP) encoding regions are retained by AT-rich genomes C_LIO_LIPP motif conservation hints at regulatory mechanisms and required translation pauses C_LIO_LIChloroplast targeting of a (mitochondrial) translation enhancer of PP motifs C_LIO_LIMpTACO1 structure at 2.34 [A] resolution demonstrates its high level of conservation C_LI

plant biology↗

bioRxiv2025

Structure and functional analysis of CDNF-BiP interaction reveal a role in endoplasmic reticulum proteostasis regulation

Cerebral dopamine neurotrophic factor (CDNF) was identified for ability to rescue midbrain dopamine neurons and as endoplasmic reticulum (ER)-located protein that can be secreted. Structurally homologous to mesencephalic astrocyte-derived neurotrophic factor (MANF), CDNF has been shown to interact with ER-localized chaperone BiP. The ER plays a crucial role in protein synthesis, folding, and quality control, with BiP being a key player in maintaining protein homeostasis. CDNF is protective against ER stress and involved in regulating the unfolded protein response (UPR) signaling and interaction with BiP. Recent studies have shown that CDNF interacts with UPR sensor proteins PERK, IRE1, and ATF6, suggesting an overlap in CDNF binding with UPR sensors and BiP. In rodent models of Parkinsons disease (PD), CDNF protects and restores the function of brain dopamine neurons and was successful in PD phase 1 clinical studies. CDNF has shown therapeutic potential for several neurological diseases, including amyotrophic lateral sclerosis, and ischemic stroke. Despite extensive knowledge on CDNFs impact on cellular function and neuronal degeneration, its detailed molecular mechanism of action in the ER remains unclear. Here, we have characterized the CDNF interaction with BiP both structurally and functionally and solved the crystal structures of CDNF-BiP complexes to 1.5 [A] resolution, complemented with molecular dynamics simulations. Results show CDNFs role as an antagonist of BiP nucleotide exchange, and thus in its chaperone function, binding to the ADP-bound state. Finally, we show its effect on neuroprotection with stem cell-derived human dopamine neurons, highlighting its potential in neurodegenerative disease treatment.

biochemistry↗

bioRxiv2024

CDNF rescues human iPSCs-derived dopamine neurons through direct binding to unfolded protein response sensors PERK and IRE1α

Cerebral dopamine neurotrophic factor (CDNF) is an unconventional trophic factor that protects dopamine neurons in cellular and animal models of Parkinsons disease (PD). CDNF was safe and well tolerated in phase 1 clinical trials for PD treatment, and currently, its peptide analogue is under investigation in phase 1 clinical trials for PD. Despite prominent neuroprotective and neurorestorative activity, the receptors and exact mechanism of CDNF functioning have been obscure. Intracellularly acting CDNF exerts cytoprotection by attenuating endoplasmic reticulum (ER) stress and unfolded protein response (UPR). We demonstrated that this activity occurs through the direct binding of CDNF to ER transmembrane UPR sensors PERK and IRE1 for purified proteins and in cells. We identified CDNF mutants deficient for binding to UPR sensors. CDNF binding to PERK and IRE1 appeared to be crucial for the survival of mouse dopamine neurons in culture. Importantly for clinical translation, CDNF rescues human induced pluripotent stem cell-derived dopamine neurons and promotes their regeneration. CDNF binding to UPR sensors alleviated terminal UPR and promoted neurite outgrowth of human dopamine neurons through direct binding to PERK and IRE1. CDNF binding to BiP was dispensable for the neuroprotective and neurorestorative activity of CDNF. Therefore, CDNF, or small molecules mimicking its binding to UPR sensors and acting selectively on dopamine neurons with activated UPR, are promising drug candidates for PD treatment.

neuroscience↗

bioRxiv2022

Biophysical and functional characterization of K+-Cl- co-transporters from Drosophila melanogaster and Hydra vulgaris

The cation-chloride co-transporter (CCC) superfamily includes ion symporters, which co-transport monovalent cations and Cl-. CCCs have crucial roles in shaping signalling and neuronal connectivity in the vertebrate brain. K+-Cl- co-transporters (KCCs) are a subfamily of CCCs and carry out the symport of K+ and Cl- ions across the plasma membrane. The KCC proteins are involved in various physiological processes, such as cell volume regulation, transepithelial ion transport, synapse formation and signal transmission, and blood pressure regulation. Among KCCs, KCC2 has gained attention because of its unique and crucial functions in the central nervous system neuronal network. Loss of activity of this transporter has been associated with several neurological disorders including schizophrenia, epilepsy, and chronic pain. On the other hand, only a limited number of studies of KCCs have been published for invertebrates. Among invertebrate proteins, the Drosophila melanogaster KCC (DmKCC) has been studied most and suggested critical for neuronal transmission. Also Cnidarian Hydra vulgaris has been shown to have a functional KCC (HvKCC). Comparative analyses of these transporters with vertebrate ones and understanding functional and biophysical aspects of them as a model system can help understand the KCC mechanism of ion transport and its regulation and evolution broadly. In this study, we chose DmKCC and HvKCC as model systems and purified DmKCC and HvKCC from Sf9 insect cells and characterized their biophysical properties with differential scanning fluorimetry and light scattering techniques. We tested their functionality using a fluorescence assay and developed a method to measure recombinant KCC ion transport activity with flame photometry.

biochemistry↗

bioRxiv2020

Structural basis of SALM3 dimerization and synaptic adhesion complex formation with PTPσ

Synaptic adhesion molecules play an important role in the formation, maintenance and refinement of neuronal connectivity. Recently, several leucine rich repeat (LRR) domain containing neuronal adhesion molecules have been characterized including netrin G-ligands, SLITRKs and the synaptic adhesion-like molecules (SALMs). Dysregulation of these adhesion molecules have been genetically and functionally linked to various neurological disorders. Here we investigated the molecular structure and mechanism of ligand interactions for the postsynaptic SALM3 adhesion protein with its presynaptic ligand, receptor protein tyrosine phosphatase {sigma} (PTP{sigma}). We solved the crystal structure of the dimerized leucine rich repeat (LRR) domain of SALM3, revealing the conserved structural features and mechanism of dimerization. Furthermore, we determined the complex structure of SALM3 with PTP{sigma} using small angle X-ray scattering, revealing a 2:2 complex similar to that observed for SALM5. Solution studies unraveled additional flexibility for the complex structure, but validated the uniform mode of action for SALM3 and SALM5 to promote synapse formation. The relevance of the key interface residues was further confirmed by mutational analysis with cellular binding assays and artificial synapse formation assays. Collectively, our results suggest that SALM3 dimerization is a pre-requisite for the SALM3-PTP{sigma} complex to exert synaptogenic activity.

biochemistry↗

bioRxiv2017

The structure of SALM5 suggests a dimeric assembly for the presynaptic RPTP ligand recognition

Synaptic adhesion molecules play a crucial role in the regulation of synapse development and maintenance. Recently several families of leucine rich repeat domain containing neuronal adhesion molecules have been characterized, including netrin G-ligands, LRRTMs, and the SALM family proteins. Most of these are expressed at the excitatory glutamatergic synapses, and dysfunctions of these genes are genetically linked with cognitive disorders, such as autism spectrum disorders and schizophrenia. The SALM family proteins SALM3 and SALM5, similar to SLITRKs, have been shown to bind to the presynaptic receptor protein tyrosine phosphatase (RPTP) family ligands. Here we present the 3 [A] crystal structure of the SALM5 LRR-Ig domain construct, and biophysical studies that verify the crystallographic results. We show that both SALM3 and SALM5 extracellular domains form similar dimeric structures, in which the LRR domains form the dimer interface. Both proteins bind to the RPTP lg-domains with micromolar affinity. SALM3 shows a clear preference for RPTP-ligands with the meB splice insert. This is in accordance with previous results showing that the LRR domain is also required for the ligand binding. Our structural studies and sequence conservation analysis suggests a ligand binding site and mechanism for RPTP binding via the dimeric LRR domain region.

biochemistry↗