Little is known of the plant branched-chain α-ketoacid
dehydrogenase complex. We have undertaken a detailed study
of the structure of the dihydrolipoyl acyltransferase (BCE2)
subunit that forms the core of the complex, to which two
other enzymes attach. Mature Arabidopsis thaliana
BCE2 was expressed in Escherichia coli. The soluble
recombinant protein was purified using a Superose 6 size-exclusion
column to >90% homogeneity and was catalytically active.
The recombinant protein formed a stable complex with a
native molecular mass of 0.95 MDa and an S coefficient
of 19.4, consistent with formation of a 24-mer. Negative-staining
transmission electron microscopy of the recombinant protein
confirmed that BCE2 forms a core with octagonal symmetry.
Despite divergence of mammalian and plant BCE2s, there
is clearly conservation of structure that is independent
of primary sequence.