Fig. 4

Structural mutations observed in ΔproA and ΔproB experiments analyzed in relation to ArgE underground activity. a Metabolic pathway maps related to ΔproA and ΔproB false positive cases. Both are involved in L-proline synthesis. Model simulations predict using an alternate pathway related to arginine and ornithine synthesis to rescue a proA/proB deficient E. coli strain. Mutations were observed in the coding regions of the metabolic genes argD and glnA. It is suggested that reduced flux through these enzymes increases flux through the ArgE associated underground activity, thus increasing production of L-proline and allowing for cell growth. b Mutation analysis in relation to the glutamine synthetase (GlnA) protein structure. An I-Tasser-predicted protein structure is provided [55] and the amino acid residue associated with observed glnA mutations in the ΔproB populations are highlighted in red. Those residues associated with ligand binding based on the crystal structure of the Salmonella typhimurium GlnA enzyme [56] are highlighted in blue. The mutations appear to be in buried regions of the homo-dodecameric enzyme at the interface of chain-chain interactions