LRP: A nucleoid-associated protein with gene regulatory functions

The Escherichia coli Leucine-responsive regulatory protein (Lrp) is a nucleoid-associated protein involved in the transcriptional regulation of 10% of all E. coli genes. The structural and biochemical properties of Lrp suggest roles in both the organization of the bacterial chromosome as well as transcriptional regulation. Lrp adopts higher order oligomerization states and shows low sequence specificity, similar to other nucleoid-associated proteins. However, Lrp transcriptionally regulates several E. coli genes, including those involved in metabolic pathways and those involved in virulence. As its name suggests, leucine affects the ability of Lrp to bind certain sequences and regulate certain genes yet many Lrp-regulated genes are not affected by the presence of leucine. Lrp homologs are found in both Gram-positive and Gram-negative bacteria and among archaea. Crystal structures of E. coli Lrp and various homologs have revealed an octameric structure with conserved motifs in the N and C termini. The role of Lrp in transcription is influenced by such factors as nutrient availability, leucine, interactions with other proteins, and competition with other regulatory proteins for binding specific sequences. Various cellular conditions like nutrient depletion regulate the concentrations of Lrp in the cell which affects the oligomeric state of the protein, influencing its ability to bind to certain sequences.