National Center for
2LFV: Solution Structure of the SPOR domain from E. coli DamX
Nuclear magnetic resonance solution structure of the peptidoglycan-binding SPOR domain from Escherichia coli DamX: insights into septal localization
Biochemistry (2013) 52 p.627-639
SPOR domains are present in thousands of bacterial proteins and probably bind septal peptidoglycan (PG), but the details of the SPOR-PG interaction have yet to be elucidated. Here we characterize the structure and function of the SPOR domain for an Escherichia coli division protein named DamX. Nuclear magnetic resonance revealed the domain comprises a four-stranded antiparallel beta-sheet buttressed on one side by two alpha-helices. A third helix, designated alpha3, associates with the other face of the beta-sheet, but this helix is relatively mobile. Site-directed mutagenesis revealed the face of the beta-sheet that interacts with alpha3 is important for septal localization and binding to PG sacculi. The position and mobility of alpha3 suggest it might regulate PG binding, but although alpha3 deletion mutants still localized to the septal ring, they were too unstable to use in a PG binding assay. Finally, to assess the importance of the SPOR domain in DamX function, we constructed and characterized E. coli mutants that produced DamX proteins with SPOR domain point mutations or SPOR domain deletions. These studies revealed the SPOR domain is important for multiple activities associated with DamX: targeting the protein to the division site, conferring full resistance to the bile salt deoxycholate, improving the efficiency of cell division when DamX is produced at normal levels, and inhibiting cell division when DamX is overproduced.