The aspartate aminotransferase-like domain of Firmicutes MocR transcriptional regulators

• C-terminal domains of Firmicutes MocR cluster into three clades.
• Evolutionary analysis indicates conserved structural features.
• Each Firmicutes MocR clade is characterized by specific conserved residues.
• MocR effector binding site shares many features with PLP fold type-I enzymes.
• Differences with PLP enzymes may explain lack of catalytic activity

Bacterial MocR transcriptional regulators possess an N-terminal DNA-binding domain containing a conserved helix-turn-helix module and an effector-binding and/or oligomerization domain at the C-terminus, homologous to fold type-I pyridoxal 5′-phosphate (PLP) enzymes. Since a comprehensive structural analysis of the MocR regulators is still missing, a comparisons of Firmicutes MocR sequences was undertook to contribute to the understanding of the structural characteristics of the C-terminal domain of these proteins, and to shed light on the structural and functional relationship with fold type-I PLP enzymes. Results of this work suggest the presence of at least three subgroups within the MocR sequences and provide a guide for rational site-directed mutagenesis studies aimed at deciphering the structure-function relationships in this new protein family.

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