acnB

AcnB, or aconitase B, is a gene that encodes an aconitase enzyme found in many bacteria, most notably Escherichia coli. It is one of two bacterial aconitases commonly referred to as AcnA and AcnB. The AcnB protein functions as a cytosolic aconitase and participates in the same biochemical reaction as other aconitases: the reversible isomerization of citrate to isocitrate via cis-aconitate in the citric acid (TCA) cycle.

AcnB is a member of the iron-sulfur cluster-containing family of enzymes. Its catalytic activity depends on a [4Fe-4S] cluster, and the integrity of this cluster is sensitive to cellular conditions such as iron availability and oxidative stress. When the cluster is compromised, enzyme activity declines, linking AcnB function to the cell’s iron homeostasis and redox state. In many bacteria, expression of acnB is coordinated with iron-responsive regulatory networks, and small RNAs and global regulators can influence its production under iron limitation or oxidative stress.

Biological role and regulation: as part of central metabolism, AcnB contributes to the flow of carbon through the TCA cycle, supporting energy production and biosynthesis. In some organisms, AcnB can be the dominant aconitase under certain environmental conditions, with AcnA serving as a backup or condition-specific isozymes under stress or iron limitation. The relative contribution of AcnB and AcnA can reflect the cell’s nutrient status and stress level.

Distribution: the acnB gene is widespread among bacteria and is typically found alongside acnA in species that possess two aconitase enzymes. The AcnB protein structure and function are conserved features of bacterial metabolism, linking iron metabolism to central carbon processing.