Structure of a Type II SMC Wadjet Complex from Neobacillus vireti

Abstract

Structural Maintenance of Chromosomes proteins are essential DNA-folding motors that facilitate critical cellular functions, including chromosome segregation and DNA repair. Wadjet systems are prokaryotic SMC complexes specialized in cellular immunity against plasmids. Type I Wadjet systems restrict plasmids via a DNA extrusion-cleavage reaction. Two other Wadjet types (II and III) have also been identified, however, their molecular characteristics are unclear. Here, we reconstituted a representative type II Wadjet system from Neobacillus vireti. We show that this system shares substrate selection and cleavage properties with type I but exhibits distinctive structural features, including a long elbow-distal coiled coil, a channel-less hinge, and a tandem KITE subunit. These features help identify the common and distinguishing architectural elements in the family of Wadjet systems and raise intriguing questions about the evolution of prokaryotic SMC complexes.