Aspartate aminotransferase of Rhizobium leguminosarum has extended substrate specificity and metabolizes aspartate to enable N2 fixation in pea nodules.
Microbiology (Reading)
; 170(7)2024 Jul.
Article
en En
| MEDLINE
| ID: mdl-39073398
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 N2 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 60â% 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 N2 fixation in legume nodules. Consequently, we show that aspartate degradation is required for N2 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 N2 fixation in pea nodules.
Palabras clave
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Aspartato Aminotransferasas
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Rhizobium leguminosarum
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Ácido Aspártico
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Pisum sativum
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Nódulos de las Raíces de las Plantas
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Fijación del Nitrógeno
Idioma:
En
Revista:
Microbiology (Reading)
Asunto de la revista:
MICROBIOLOGIA
Año:
2024
Tipo del documento:
Article
Pais de publicación:
Reino Unido