Evolution
Comparing human and rat serine dehydratase using a cDNA library was identical except for a 36 amino acid residue. The overall homology between rat SDH and human SDH is 81% in the nucleotide sequence and 84% in the amino acid sequence. Similarities have also been shown between yeast and E.Coli threonine dehydratase and human serine dehydratase. Human SDH shows sequence homology of 27% with the yeast enzyme and 27% with the E. Coli enzyme.
Additionally, the primary structures are shown to be similar between mammalian SDH and microbial threonine dehydratase, especially in the sequences surrounding the PLP cofactor and the G-residues surrounding the PLP’s phosphate group. Thus, in PLP enzymes, there is high conservation of the active site residues during evolution. With active site sequence conservation, it is suggested that dehydratase enzymes originated from a common ancestor.
Figure 8 shows the sequence similarities of the amino acid sequence of human SDH with those of rat SDH, and yeast and E. coli threonine dehydratases. Asterisks and crosses represent sequence similarity to human SDH.
In an analysis done by Mehta and Christen from the Center for Bioinformatics and Biotechnology, the pyridoxal-5-phosphate (vitamin B6)-dependent enzymes that act on amino acid substrates have multiple evolutionary origins. The overall B6 enzymes diverged into four independent evolutionary lines: α family (i.e. aspartate aminotransferase), β family (serine dehydratase),D-alanine aminotransferase family and the alanine racemase family. An example of the evolutionary similarity in the Beta family is seen in the mechanism. The β enzymes are all lyases and catalyze reactions where Cα and Cβ participate. Overall, in the PLP-dependent enzymes, the PLP in every case is covalently attached via an imine bond to the amino group in the active site.
Figure 9 displays the evolutionary lineage of enzymes from PLP-dependent enzyme to the Beta family to SDH.
Read more about this topic: Serine Dehydratase
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