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Two Cobalt Chelatase Subunits Can Be Generated from a Single chlD Gene via Programed Frameshifting.
1Institute of Bioengineering, Federal Research Centre Fundamentals of Biotechnology, Moscow, Russia.
Molecular Biology and Evolution
|March 27, 2020
Summary
Programed ribosomal frameshifting in the chlD gene allows some bacteria and archaea to produce both medium and small subunits for cobalt chelatase (vitamin B12) and magnesium chelatase (chlorophyll) biosynthesis, even without a separate small subunit gene.
Area of Science:
- Biochemistry and Molecular Biology
- Microbial Genetics and Genomics
- Enzymology
Background:
- Magnesium chelatase (ChlIDH) and cobalt chelatase (CobNST) enzymes, crucial for (bacterio)chlorophyll and cobalamin (vitamin B12) synthesis, share subunit similarities suggesting common evolutionary origins.
- Some vitamin B12 producers utilize an atypical cobalt chelatase with a large subunit (cobN) and medium (chlD) and small (chlI) subunits from magnesium chelatase.
Purpose of the Study:
- To investigate the evolutionary and mechanistic basis of subunit composition in cobalt and magnesium chelatase enzymes across prokaryotes.
- To explore the phenomenon of missing small subunit genes in some cobalamin-producing organisms.
Main Methods:
- Bioinformatic analysis of over 1,200 diverse prokaryotic genomes from cobalamin and/or chlorophyll producers.
- Identification and analysis of gene sequences, focusing on cobN, chlD, and chlI genes.
- Statistical analysis to correlate the absence of small subunit genes with the presence of programmed ribosomal frameshifting signals in chlD genes.
Main Results:
- Many cobalamin producers possess only cobN and chlD genes, lacking a separate small subunit gene.
- A significant subset of chlD genes in these organisms contain programmed ribosomal frameshifting signals.
- Programmed ribosomal frameshifting signals in chlD genes are statistically enriched in genomes lacking small subunit genes, suggesting a mechanism for producing both subunits from a single mRNA transcript.
Conclusions:
- Programmed ribosomal frameshifting in chlD is a conserved mechanism in bacteria and archaea, enabling the production of both medium and small subunits for essential chelatase enzymes.
- This frameshifting strategy provides an alternative pathway for enzyme assembly, particularly in organisms that have lost or not acquired a dedicated small subunit gene.
- The specific frameshifting mechanisms may vary across different prokaryotic taxa, reflecting evolutionary adaptations.
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