Protein engineering reveals ancient adaptive replacements in isocitrate dehydrogenase

Antony M. Dean, G. Brian Golding

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Evolutionary analysis indicates that eubacterial NADP-dependent isocitrate dehydrogenases (EC first evolved from an NAD-dependent precursor about 3.5 billion years ago. Selection in favor of utilizing NADP was probably a result of niche expansion during growth on acetate, where isocitrate dehydrogenase provides 90% of the NADPH necessary for biosynthesis. Amino acids responsible for differing coenzyme specificities were identified from x-ray crystallographic structures of Escherichia coli isocitrate dehydrogenase and the distantly related Thermus thermophilus NAD- dependent isopropylmalate dehydrogenase. Site-directed mutagenesis at sites lining the coenzyme binding pockets has been used to invert the coenzyme specificities of both enzymes. Reconstructed ancestral sequences indicate that these replacements are ancestral. Hence the adaptive history of molecular evolution is amenable to experimental investigation.

Original languageEnglish (US)
Pages (from-to)3104-3109
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number7
StatePublished - Apr 1 1997


  • NAD
  • NADP
  • ancient adaptations
  • isopropylmalate dehydrogenase


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