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Aspartate aminotransferase of Rhizobium leguminosarum has extended substrate specificity and metabolizes aspartate to enable N 2 fixation in pea nodules.
- Source :
-
Microbiology (Reading, England) [Microbiology (Reading)] 2024 Jul; Vol. 170 (7). - Publication Year :
- 2024
-
Abstract
- Rhizobium leguminosarum aspartate aminotransferase (AatA) mutants show drastically reduced symbiotic nitrogen fixation in legume nodules. Whilst AatA reversibly transaminates the two major amino-donor compounds aspartate and glutamate, the reason for the lack of N <subscript>2</subscript> fixation in the mutant has remained unclear. During our investigations into the role of AatA, we found that it catalyses an additional transamination reaction between aspartate and pyruvate, forming alanine. This secondary reaction runs at around 60 % of the canonical aspartate transaminase reaction rate and connects alanine biosynthesis to glutamate via aspartate. This may explain the lack of any glutamate-pyruvate transaminase activity in R. leguminosarum , which is common in eukaryotic and many prokaryotic genomes. However, the aspartate-to-pyruvate transaminase reaction is not needed for N <subscript>2</subscript> fixation in legume nodules. Consequently, we show that aspartate degradation is required for N <subscript>2</subscript> fixation, rather than biosynthetic transamination to form an amino acid. Hence, the enzyme aspartase, which catalyses the breakdown of aspartate to fumarate and ammonia, suppressed an AatA mutant and restored N <subscript>2</subscript> fixation in pea nodules.
- Subjects :
- Substrate Specificity
Bacterial Proteins metabolism
Bacterial Proteins genetics
Symbiosis
Mutation
Rhizobium leguminosarum genetics
Rhizobium leguminosarum metabolism
Rhizobium leguminosarum enzymology
Aspartic Acid metabolism
Pisum sativum microbiology
Root Nodules, Plant microbiology
Nitrogen Fixation
Aspartate Aminotransferases metabolism
Aspartate Aminotransferases genetics
Subjects
Details
- Language :
- English
- ISSN :
- 1465-2080
- Volume :
- 170
- Issue :
- 7
- Database :
- MEDLINE
- Journal :
- Microbiology (Reading, England)
- Publication Type :
- Academic Journal
- Accession number :
- 39073398
- Full Text :
- https://doi.org/10.1099/mic.0.001471