A Biophysical Analysis of Malate Dehydrogenase and Citrate Synthase Protein‐Protein Interaction

The metabolon theory describes the protein interactions of enzymes regulating a metabolic pathway. Through these interactions proteins can share substrates through direct channeling. One set of enzymes that are involved in metabolon complexes are citrate synthase and malate dehydrogenase. This study attempts to understand the interactions regulating the metabolon of malate dehydrogenase (MDH) and citrate synthase (CS), which are integral intermediate metabolic enzymes. Using size exclusion chromatography and sedimentation, previous studies identified the interaction between CS and MDH to be isoform specific, but no further work has been conducted to obtain affinity values or the biophysical nature of the interaction. Codon optimized His tagged recombinant proteins were expressed and purified using affinity chromatography. These enzymes include: glyoxysomal malate dehydrogenase (gMDH), human cytosolic malate dehydrogenase (MDH1), human mitochondrial malate dehydrogenase (MDH2), and human mitochondrial citrate synthase (CS). We analyzed the protein interactions using fast thermal melts which further explain the thermal stability of the the dimerization of the metabolons. We first show that protein concentration did not induce oligomerization of CS or any MDH isoform, indicating that any changes are not from MDH or CS homodimerization. Next, we investigated specific CS‐MDH interactions using fast thermal melts. The results show that from the initial melting temperature of CS, the addition of mitochondrial MDH had a greater shift in its melting temperature than the addition of cytosolic MDH, by 3–4°C. The melting point of CS was not altered in the presence of the plant MDH isoform. This indicates a specific and dramatic set of contacts for mitochondrial MDH and CS. However unlike the information found in the literature there was still a measurable shift in melting point when cytosolic MDH was incubated with CS. Overall this shows for the first time a quantifiable interaction between proteins in a well‐established pathway that will allow the further dissection of these interactions. Support or Funding Information Support for this project was from NSF REU 146045 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .