Functional insights into nucleoside diphosphate kinases encoded by two ndk paralogs in Waddlia chondrophila

The Chlamydiota phylum consists of obligate intracellular bacteria, including well-known pathogens and emerging environmental species, with diverse host ranges and metabolic capabilities. Among these bacteria, the gene, which encodes nucleoside diphosphate kinase (ndk), is present in variable copy numbers. While most chlamydial species carry a single copy of ndk, some species have two copies. In W. chondrophila, the two Ndk proteins encoded by ndk paralogs retain conserved kinase motifs but differ in subcellular localization, suggesting divergent functional roles. According to localization studies performed in heterologous expression systems, WcNdk1 is confined to the inclusion and probably supports nucleotide metabolism, while WcNdk2 localizes to the host nucleus, perinuclear space, and Golgi apparatus, suggesting involvement in host interaction. Azidothymidine (AZT), a known Ndk inhibitor, impaired W. chondrophila growth, potentially through inhibition of WcNdk2. However, the lack of genetic tools and the absence of in vitro enzymatic assays currently limit definitive functional conclusions. Our data suggest potential functions for Ndks in W. chondrophila, providing a foundation for future studies on Ndk-mediated interactions between this pathogen and its host.