The catalytic domain of DNase II and similar proteins.

DNase II contains two copies of a variant HKD motif, where the aspartic acid residue is variable; the motifs are distributed in both the N- and C-terminus domains (black arrows). The catalytic centre of DNase II is formed by the two variant HKD motifs in the form of a pseudodimer.脱氧核糖核酸酶II（DNase II）包含两个拷贝的变异型HKD基序（HKD motif），其中天冬氨酸残基具有可变性；该基序分布于N端结构域与C端结构域中（以黑色箭头标注）。脱氧核糖核酸酶II的催化中心由这两个变异型HKD基序以假二聚体的形式构成。