Human lysosomal DNase IIalpha contains two requisite PLD-signature (HxK) motifs: evidence for a pseudodimeric structure of the active enzyme species.

Lysosomal DNase IIalpha is essential for DNA waste removal and auxiliary apoptotic DNA fragmentation in higher eukaryotes. Despite the key role of this enzyme, little is known about its structure-function relationships. Here, mutational and biochemical analyses were used to characterize human DNase IIalpha variants expressed in mammalian cells. The resulting data strongly support the hypothesis that the enzyme is a monomeric phospholipase D-family member with a pseudodimeric protein fold. According to our results, DNase IIalpha contains two requisite PLD-signature motifs ((113)HTK(115) and (295)HSK(297)) in the N- and C-terminal subdomains, respectively, that together form a single active site. Based on these data, we present an experimentally validated structural model of DNase IIalpha.