An evolutionary conserved lysine acetylation hotspot regulates plant mitochondrial malate dehydrogenase activity

Plants need to be able to rapidly and flexibly adjust their metabolism to changes their immediate environment. Since this necessity results from the sessile lifestyle of land plants, key mechanisms of orchestrating central metabolic acclimation are likely to have evolved early. Here we explore the role of lysine acetylation as a posttranslational modification to directly modulate metabolic function. First, we generate a lysine acetylome of the early divergent land plant Physcomitrium (Physcomitrella) patens. We identify 638 lysine acetylation sites, which were predominant in the mitochondria and plastids. A comparison with different angiosperms, including Arabidopsis thaliana, pinpoints lysine acetylation as conserved strategy in land plants. We focus on modified enzymes involved in mitochondrial central metabolism and select the mitochondrial malate dehydrogenase (mMDH), which acts as a hub of plant metabolic flexibility. In P. patens we detected a unique lysine acetylated site located next to one of the four acetylation sites detected in A. thaliana mMDH1. We assessed the kinetic behavior of recombinant A. thaliana and P. patens mMDHs with site-specifically incorporated acetyllysines. While the sites K325, K329 and K334 do not show any changes in the catalytic properties as assessed by oxaloacetate reduction activity, acetylation of A. thaliana mMDH1 at K170 markedly decreases its activity and acetylation of P. patens mMDH1 at K172 increases it. In both cases, acetylation induces modifications of the turnover number of the enzymes, without modifying the affinity for the substrates. Homology modelling of the mMDH1 proteins reveals a hotspot of lysine acetylation that is distant from the active site and homomerisation interfaces but conserved in land plants. The data reveal lysine acetylation as a strategy to tune the enzymatic properties of central metabolic enzymes with likely impact on metabolic capacity and flexibility to underpin plant acclimation.

Evaluation of Human Cerebrospinal Fluid Malate Dehydrogenase 1 as a Marker in Genetic Prion Disease Patients

The exploration of accurate diagnostic markers for differential diagnosis of neurodegenerative diseases is an ongoing topic. A previous study on cerebrospinal fluid (CSF)-mitochondrial malate dehydrogenase 1 (MDH1) in sporadic Creutzfeldt–Jakob disease (sCJD) patients revealed a highly significant upregulation of MDH1. Here, we measured the CSF levels of MDH1 via enzyme-linked immunosorbent assay in a cohort of rare genetic prion disease cases, such as genetic CJD (gCJD) cases, exhibiting the E200K, V210I, P102L (Gerstmann–Sträussler–Scheinker syndrome (GSS)), or D178N (fatal familial insomnia (FFI)) mutations in the PRNP. Interestingly, we observed enhanced levels of CSF-MDH1 in all genetic prion disease patients compared to neurological controls (without neurodegeneration). While E200K and V210I carriers showed highest levels of MDH1 with diagnostic discrimination from controls of 0.87 and 0.85 area under the curve (AUC), FFI and GSS patients exhibited only moderately higher CSF-MDH1 levels than controls. An impact of the PRNP codon 129 methionine/valine (MV) genotype on the amount of MDH1 could be excluded. A correlation study of MDH1 levels with other neurodegenerative marker proteins revealed a significant positive correlation between CSF-MDH1 concentration with total tau (tau) but not with 14-3-3 in E200K, as well as in V210I patients. In conclusion, our study indicated the potential use of MDH1 as marker for gCJD patients which may complement the current panel of diagnostic biomarkers.