The hypothetical protein ‘Alr3200’ of Anabaena sp. strain PCC7120 is highly conserved among cyanobacterialspecies. It is a member of the DUF820 (Domain of Unknown Function) protein family, and is predicted to have aDNase domain. Biochemical analysis revealed a Mg(II)-dependent DNase activity for Alr3200 with a specific activityof 8.62×104 Kunitz Units (KU) mg−1 protein. Circular dichroism analysis predicted Alr3200 to have ~40% β-strandsand ~9% α-helical structures. Anabaena PCC7120 inherently expressed Alr3200 at very low levels, and its overexpressionhad no significant effect on growth of Anabaena under control conditions. However, Analr3200+, therecombinant Anabaena strain overexpressing Alr3200, exhibited zero survival upon exposure to 6 kGy of γ-radiation,which is the LD50 for wild type Anabaena PCC7120 as well as the vector control recombinant strain, AnpAM.Comparative analysis of the two recombinant Anabaena strains suggested that it is not the accumulated Alr3200 perse, but its possible interactions with the radiation-induced unidentified DNA repair proteins of Anabaena, whichhampers DNA repair resulting in radiosensitivity.
Volume 45, 2020
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