enzyme catalyzing nitrogen fixation in bacteria root nodules on legumes
TRANSCRIPT
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Enzyme catalyzing Nitrogen Fixation in Bacteria
Root nodules on legumes
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Nitrogenase is the enzyme found in a variety of bacteria, some of them symbiotic with
plants
• catalyzes the conversion of molecular nitrogen (N2) from the air into ammonia (NH3).
• It is found in a variety of bacteria, some of them symbiotic with plants.
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Diversity of N-fixing Bacteria
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Choosing the sequence to compare
• Nitrogenase consists of a molybdenum-iron (MoFe) protein and an iron (Fe) protein. The MoFe protein contains 2 alpha protein chains and 2 beta protein chains.
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Trials and Errors
• Constructed a phylogenetic tree of the Mo-Fe protein of nitrogenase from published nucleic acid data.
• Tried to get a more coherent tree by eliminating some of the sequences.
• Tree still not revealing.• Mistake: using nucleotides, switched to amino acid
sequences for the alpha and beta chains.
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Amino Acid sequence
• Obtained amino acid sequence of alpha and beta subunits of MoFe protein from Azotobacter vinelandii
• Did an alignment on alpha and beta subunits and found 20.1% identity and , 78% global alignment, suggesting that alpha and beta chains are the product of gene duplication.
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Crystallographic structure
• Found crystallographic structure for MoFe protein from A. vinelandii shown on next slide.
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• Structure Explorer - 1M34
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Gene Duplication in the Mo-Fe Protein of Nitrogenase
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Figure 54.18 The nitrogen cycle
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Figure 37.9 The role of soil bacteria in the nitrogen nutrition of plants (Layer 3)
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Figure 37.10 Root nodules on legumes
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Figure 37.10x Nodules
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Figure 37.11 Development of a soybean root nodule
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Figure 37.13 Molecular biology of root nodule formation
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Figure 37.12 Crop rotation and “green manure”
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Figure 27.11 One of the most independent organisms on earth: Cyanobacteria (Anabaena)
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Figure 27.11x1 Cyanobacteria: Gloeothece (top left), Nostoc (top right), Calothrix (bottom left), Fischerella (bottom right)
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Figure 27.11x2 A bloom of cyanobacteria
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Nutrient Deficiencies: Agricultural Importance
Nitrogen deficiency
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Figure 54.9 Nutrient addition experiments in a Hudson Bay salt marsh
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Figure 27.8 Specialized membranes of prokaryotes