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Proteobacterial histidine-biosynthetic pathways are paraphyletic
1Department of Microbiology and Molecular Genetics, Markey Center for Molecular Genetics, University of Vermont College of Medicine, Burlington 05405, USA. jbond@zoo.uvm.edu
Journal of Molecular Evolution
|May 5, 2000
Summary
HisZ, a protein in histidine biosynthesis, is related to histidyl-tRNA synthetase but lacks tRNA function. Its presence/absence in bacteria suggests evolutionary loss and horizontal gene transfer in histidine pathway regulation.
Area of Science:
- Biochemistry
- Evolutionary Biology
- Microbial Genetics
Background:
- HisZ protein in Lactococcus lactis shares sequence identity with histidyl-tRNA synthetase (HisRS) but lacks aminoacylation activity.
- HisZ homologs are found in diverse bacteria but absent in others, suggesting evolutionary divergence.
Purpose of the Study:
- To investigate the evolutionary history and functional significance of HisZ proteins within the histidine biosynthesis pathway.
- To explore the role of horizontal gene transfer in the evolution of histidine biosynthesis regulation.
Main Methods:
- Phylogenetic analysis of HisRS and HisRS-like protein families.
- Phylogenetic analysis of ATP-PRPP transferase (HisG) and histidinol dehydrogenase (HisD) sequences.
- Comparative genomics to assess the distribution of HisZ across bacterial taxa.
Main Results:
- HisZ proteins form a distinct monophyletic group outside the main bacterial HisRS clade, supporting a model of evolutionary loss.
- The distribution of HisZ correlates with the paraphyly of HisG and HisD sequences in Proteobacteria.
- HisZ and HisG are essential for the initial step of histidine biosynthesis, involving ATP-PRPP transferase activity.
Conclusions:
- The evolutionary trajectory of HisZ suggests it was lost in certain bacterial lineages.
- Horizontal gene transfer appears to be a significant factor in the evolution of histidine biosynthesis regulation, particularly in Proteobacteria.