Protein engineering reveals ancient adaptive replacements in isocitrate dehydrogenase.
Evolutionary analysis indicates that eubacterial NADP-dependent isocitrate dehydrogenases (EC 1.1.1.42) 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.
Dean
A M
AM
Department of Biological Chemistry, The Chicago Medical School, North Chicago, IL 60064-3095, USA.
Golding
G B
GB
D000595:Amino Acid Sequence; D007521:Isocitrate Dehydrogenase / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009249:NADP / Q000378:metabolism; D010802:Phylogeny; D015202:Protein Engineering; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
D009249:NADP; D007521:Isocitrate Dehydrogenase