dikinases

Dikinases are a group of enzymes first identified in 2019 during a systematic survey of bacterial protein phosphorylation pathways. The name derives from the fact that most members contain two distinct protein kinase domains arranged serially within a single polypeptide chain. Each domain is structurally related to classical serine/threonine kinases but has evolved specialized catalytic features that allow the enzyme to act on two distinct substrates in a single catalytic cycle.

The most studied dikinase, DkiA from the soil bacterium Bacillus subtilis, contains an N‑terminal kinase domain that is specific for the response regulator Spo0F and a C‑terminal domain that phosphorylates the metabolic enzyme YnmT. The dual-activity allows coordination of sporulation signalling with central metabolism. In vitro assays show that Spo0F phosphorylation is strictly dependent on YnmT being in its phosphorylated state, indicating a regulatory feedback loop.

Phylogenetic analysis places dikinases in a distinct clade separate from the single‑domain protein kinases and the bacterial histidine kinases that mediate two‑component signalling. Sequence alignments reveal that the internal linker region is highly variable but often contains helix‑turn‑helix motifs that may act in substrate recognition. No dikinase homolog has been reported in eukaryotes, suggesting the family is confined to prokaryotes.

In addition to B. subtilis, dikinase homologs have been found in several Actinobacteria and Firmicutes, but their biochemical properties differ. Some lack the YnmT‑dependent regulation and instead appear to act on transcription factors involved in cell envelope stress responses.

Functional studies using gene deletion mutants indicate that loss of dikinase activity leads to reduced sporulation efficiency and altered growth rates under nutrient limitation. Complementation with catalytically inactive versions fails to rescue the phenotype, underscoring the importance of both kinase domains.

Because the biochemical mechanisms by which dikinases integrate two signalling pathways remain incompletely understood, the enzymes continue to be a focus of enzymology and systems biology research. Ongoing work aims to determine crystal structures, identify additional substrates, and explore potential roles in industrial biotechnology and antimicrobial development.