A novel nucleic acid-binding protein, Gp49, from mycobacteriophage with mycobactericidal activity has the potential to be a therapeutic agent

The mycobacteriophages encode unique proteins that are potent to be therapeutic agents. We screened several clones with mycobactericidal properties from a genomic library of mycobacteriophages. Here we report the properties of one such clone coding the gene product, Gp49, of the phage Che12. Gp49 is a 16 kD dimeric protein having an HTH motif at its C-terminal and is highly conserved among mycobacteriophages and likely to be part of phage DNA replication machinery. Alphafold predicts it to be an alpha-helical protein. However, its CD spectrum showed it to be predominantly beta-sheeted. It is a high-affinity heparin-binding protein having similarities with the macrophage protein Azurocidin. Its beta-sheeted apo-structure gets transformed into alpha-helix upon binding to hep-arin. It binds to linear dsDNA as well as ssDNA and RNA cooperatively in a sequence non-specific manner. This DNA binding property enables it to inhibit both in vitro and in vivo transcription. The c-terminal HTH motif is responsible for binding to both heparin and nucleic acids. Its in vivo localization on DNA could cause dis-placements of many DNA-binding proteins from the bacterial chromosome. We surmised that the bactericidal activity of Gp49 arises from its non-specific DNA binding leading to the inhibition of many host-DNA-dependent processes. Its heparin-binding ability could have therapeutic/diagnostic usages in bacterial sepsis treatment.

Automated summary

We screened a clone from a genomic library of mycobacteriophages and found it to have mycobactericidal properties. This clone codes for a protein called Gp49, which is highly conserved among mycobacteriophages and likely plays a role in phage DNA replication. Gp49 is a high-affinity heparin-binding protein that can bind to both linear dsDNA and ssDNA/cooperatively, inhibiting transcription and displacing DNA-binding proteins. Its heparin-binding ability could have therapeutic/diagnostic applications in bacterial sepsis treatment.