Crystal structure of the cytosolic Nudix-like domain of CD-NTase-associated protein 16 from Enterococcus faecalis

Abstract

The cyclic oligonucleotide-based antiphage signaling system (CBASS) employs diverse effector proteins to trigger abortive infection upon phage invasion, yet structural information on membrane-associated CBASS effectors remains limited. CD-NTase-associated protein 16 from Enterococcus faecalis (EfCap16) is a predicted CBASS effector comprising an N-terminal transmembrane region and a C-terminal Nudix-like domain. Here, we report the recombinant expression, purification, crystallization and X-ray crystal structure of the cytosolic Nudix domain of EfCap16 (PDB entry 22lg) in space group P12₁1. The protein was purified to homogeneity and crystallized, and its structure was determined at 1.6 Å resolution. The EfCap16 Nudix domain shares structural similarity with the Nudix superfamily and contains a conserved Nudix motif. This structure provides a reference framework for future biochemical and functional studies of transmembrane CBASS effectors.