GTP-dependent polymerization of the tubulin-like RepX replication protein encoded by the pXO1 plasmid of Bacillus anthracis

• Published in: Molecular microbiology Vol. 67; no. 4; pp. 881 - 890
• Main Authors: Anand, Syam P, Akhtar, Parvez, Tinsley, Eowyn, Watkins, Simon C, Khan, Saleem A
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.02.2008; Blackwell Publishing Ltd
• Subjects: Bacillus anthracis - genetics; Bacillus anthracis - metabolism; Bacteria; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Biochemistry; Biopolymers; Cytoskeletal Proteins - chemistry; Cytoskeletal Proteins - genetics; Cytoskeletal Proteins - metabolism; Cytoskeleton - genetics; Cytoskeleton - metabolism; Cytoskeleton - ultrastructure; Deoxyribonucleic acid; DNA; DNA Replication; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Genes, Bacterial; GTP Phosphohydrolases - chemistry; GTP Phosphohydrolases - genetics; GTP Phosphohydrolases - metabolism; Guanosine Triphosphate - metabolism; Microscopy, Electron, Transmission; Mutation; Plasmids - genetics; Proteins; Tubulin - chemistry; Tubulin - metabolism
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/j.1365-2958.2007.06100.x

RepX protein encoded by the pXO1 plasmid of Bacillus anthracis is required for plasmid replication. RepX harbours the tubulin signature motif and contains limited amino acid sequence homology to the bacterial cell division protein FtsZ. Although replication proteins are not known to polymerize, here we show by electron microscopy that RepX undergoes GTP-dependent polymerization into long filaments. RepX filaments assembled in the presence of GTPγS were more stable than those assembled in the presence of GTP, suggesting a role for GTP hydrolysis in the depolymerization of the filaments. Light scattering studies showed that RepX underwent rapid polymerization, and substitution of GTP with GTPγS stabilized the filaments. RepX exhibited GTPase activity and a mutation in the tubulin signature motif severely impaired its GTPase activity and its polymerization in vitro. Unlike FtsZ homologues, RepX harbours a highly basic carboxyl-terminal region and exhibits GTP-dependent, non-specific DNA binding activity. We speculate that RepX may be involved in both the replication and segregation of the pXO1 plasmid.