title: Nuclear magnetic resonance solution structure of the peptidoglycan-binding SPOR domain from Escherichia coli DamX: insights into septal localization.
abstract: 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 β-sheet buttressed on one side by two α-helices. A third helix, designated α3, associates with the other face of the β-sheet, but this helix is relatively mobile. Site-directed mutagenesis revealed the face of the β-sheet that interacts with α3 is important for septal localization and binding to PG sacculi. The position and mobility of α3 suggest it might regulate PG binding, but although α3 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.
authors.affiliation: Department of Microbiology, Carver College of Medicine, The University of Iowa, Iowa City, IA 52242, USA.
authors.forename: Kyle B
authors.initials: KB
authors.lastname: Williams
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yahashiri
authors.forename: S J Ryan
authors.initials: SJ
authors.lastname: Arends
authors.forename: David L
authors.initials: DL
authors.lastname: Popham
authors.forename: C Andrew
authors.initials: CA
authors.lastname: Fowler
authors.forename: David S
authors.initials: DS
authors.lastname: Weiss
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002455:Cell Division; D017124:Conserved Sequence; D003840:Deoxycholic Acid / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D019906:Nuclear Magnetic Resonance, Biomolecular; D010457:Peptidoglycan / Q000737:chemistry*; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D013499:Surface Properties
chemical_list: C545719:DamX protein, E coli; D029968:Escherichia coli Proteins; D010457:Peptidoglycan; D003840:Deoxycholic Acid