A unique fungal lysine biosynthesis enzyme shares a common ancestor with tricarboxylic acid cycle and leucine biosynthetic enzymes found in diverse organisms |
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Authors: | Steven D Irvin Jnanendra K Bhattacharjee |
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Institution: | (1) Department of Microbiology, 32 Pearson Hall, Miami University, Oxford, OH 45056, USA, US |
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Abstract: | Fungi have evolved a unique α-aminoadipate pathway for lysine biosynthesis. The fungal-specific enzyme homoaconitate hydratase
from this pathway is moderately similar to the aconitase-family proteins from a diverse array of taxonomic groups, which have
varying modes of obtaining lysine. We have used the similarity of homoaconitate hydratase to isopropylmalate isomerase (serving
in leucine biosynthesis), aconitase (from the tricarboxylic acid cycle), and iron-responsive element binding proteins (cytosolic
aconitase) from fungi and other eukaryotes, eubacteria, and archaea to evaluate possible evolutionary scenarios for the origin
of this pathway. Refined sequence alignments show that aconitase active site residues are highly conserved in each of the
enzymes, and intervening sequence sites are quite dissimilar. This pattern suggests strong purifying selection has acted to
preserve the aconitase active site residues for a common catalytic mechanism; numerous other substitutions occur due to adaptive
evolution or simply lack of functional constraint. We hypothesize that the similarities are the remnants of an ancestral gene
duplication, which may not have occurred within the fungal lineage. Maximum likelihood, neighbor joining, and maximum parsimony
phylogenetic comparisons show that the α-aminoadipate pathway enzyme is an outgroup to all aconitase family proteins for which
sequence is currently available.
Received: 7 October 1997 |
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Keywords: | : Homoaconitate hydratase — Homoaconitase — Lysine biosynthesis — α -Aminoadipate pathway — Molecular evolution — Amino acid metabolism — Gene duplication — Adaptive evolution — Evolutionary origin |
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