Enzyme catalyzing Nitrogen Fixation in Bacteria Root nodules on legumes

Enzyme catalyzing Nitrogen Fixation in Bacteria

Root nodules on legumes

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.

Diversity of N-fixing Bacteria

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.

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.

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.

Crystallographic structure

• Found crystallographic structure for MoFe protein from A. vinelandii shown on next slide.

• Structure Explorer - 1M34

Gene Duplication in the Mo-Fe Protein of Nitrogenase

Figure 54.18 The nitrogen cycle

Figure 37.9 The role of soil bacteria in the nitrogen nutrition of plants (Layer 3)

Figure 37.10 Root nodules on legumes

Figure 37.10x Nodules

Figure 37.11 Development of a soybean root nodule

Figure 37.13 Molecular biology of root nodule formation

Figure 37.12 Crop rotation and “green manure”

Figure 27.11 One of the most independent organisms on earth: Cyanobacteria (Anabaena)

Figure 27.11x1 Cyanobacteria: Gloeothece (top left), Nostoc (top right), Calothrix (bottom left), Fischerella (bottom right)

Figure 27.11x2 A bloom of cyanobacteria

Nutrient Deficiencies: Agricultural Importance

Nitrogen deficiency

Figure 54.9 Nutrient addition experiments in a Hudson Bay salt marsh

Figure 27.8 Specialized membranes of prokaryotes