Regulation of ultraviolet radiation induced cutaneous photoimmunosuppression by toll-like receptor-4

The open reading frame alr3199 of the nitrogen-fixing cyanobacterium, Anabaena sp. strain PCC7120 was cloned and overexpressed in Escherichia coli. Purified recombinant Alr3199 protein was found to be a functionally active deoxyribonuclease with novel features, such as (1) no homology to typical DNases (2) a Ca²⁺-dependent Nickase activity (3) presence of a di-hemerythrin domain, and (4) requirement of Fe²⁺ conjugated to hemerythrin domains for optimal activity. Both the DNase and Nickase activities were found to be associated with the N-terminal non-hemerythrin region, but were modulated by Fe²⁺ conjugated to the C-terminal hemerythrin region. This is the first report of a hemerythrin protein with DNase activity, tentatively designated as ‘HE-DNase’, and with a possible role in stress-induced DNA damage/repair in Anabaena.