ChrII-Encoded DNA Helicase: A Preliminary Study

Background: DNA helicases are unwinding enzymes that are essential for many cellular processes. Research has suggested that both the model microorganisms of a single chromosome and the model microorganisms of multiple chromosomes adopt DNA helicases encoded by chromosome I. Therefore, studying DNA helicases encoded by chromosome II may lay some foundation for understanding nucleic acid metabolism processes. Objective: To prove the existence of DNA helicase encoded by chromosome II and to reveal its difference compared to DNA helicase encoded by chromosome I. Methods: The DNA helicases of Pseudoalteromonas spongiae JCM 12884^T and Pseudoalteromonas tunicata DSM 14096^T were analyzed by sequence alignment and phylogenetic relationships with other known DNA helicases. Then, proteins of P. spongiae JCM 12884^T and P. tunicata DSM 14096^T were obtained by heterologous expression. N-terminal sequencing and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis were performed to confirm the form of proteins. A fluorescence resonance energy transfer (FRET) assay was used to measure the activity of helicases. Results: DnaB-pspo and DnaB-ptun belong to the same family, the PRK08840 superfamily, and form a branch with helicases encoded by chromosome I. YwqA-pspo and YwqA-ptun have similar domains and form another branch with helicases encoded by chromosome II. All four helicases have DNA unwinding activity. YwqA is more efficient than DnaB for DNA unwinding, especially YwqA-pspo, which is encoded by bidirectional replication chromosome II. Conclusion: This is the first study to show that the existence of a DNA helicase encoded by chromosome II, and DNA helicase encoded by chromosome II is more efficient than chromosome I for DNA unwinding.