A Comparison of the GroE Chaperonin Requirements for Sequentially and Structurally Homologous Malate Dehydrogenases

Escherichia coli malate dehydrogenase (EcMDH) and its eukaryotic counterpart, porcine mitochondrial malate dehydrogenase (PmMDH), are highly homologous proteins with significant sequence identity (60%) and virtually identical native structural folds. Despite this homology, EcMDH folds rapidly and efficiently in vitro and does not seem to interact with GroE chaperonins at physiological temperatures (37 °C), whereas PmMDH folds much slower than EcMDH and requires these chaperonins to fold to the native state at 37 °C. Double jump experiments indicate that the slow folding behavior of PmMDH is not limited by proline isomerization. Although the folding enhancer glycerol (