title: Insights into molecular plasticity of choline binding proteins (pneumococcal surface proteins) by SAXS.
abstract: Phosphocholine moieties decorating the pneumococcal surface are used as a docking station for a family of modular proteins, the so-called choline binding proteins or CBPs. Choline recognition is essential for CBPs function and may also be a determinant for their quaternary structure. There is little knowledge about modular arrangement or oligomeric structures in this family. Therefore, we have used the small angle X-ray scattering (SAXS) technique combined with analytical ultracentrifugation in order to model the three-dimensional envelope of two highly different CBPs: the phage encoded Cpl-1 lysozyme and the pneumococcal phosphorylcholine esterase Pce. Both enzymes have an N-terminal catalytic module and a C-terminal choline-binding module (CBM) that attaches them to the bacterial surface and comprises six and ten sequence repeats in Cpl-1 and Pce, respectively. SAXS experiments have shown an inherent conformational plasticity in Cpl-1 that accounts for the different relative position of these regions in the solution and crystal structures. Dimerization of Cpl-1 upon choline binding has been also visualised for the first time, and monomer-monomer interactions take place through the first CBR where a non-canonical choline binding site has now been identified. This mode of association seems to be independent of the absence or presence of the Cpl-1 catalytic module and reveals that the arrangement of the monomers differs from that previously found in the isolated CBM dimer of pneumococcal LytA amidase. In contrast, Pce displays the same modular disposition in the solution and crystal structures, and remains almost invariant upon choline binding. The present results suggest that protein dimerization and duplication of CBRs may be alternative but not equivalent ways of improving cell wall recognition by CBPs, since they provide different interaction geometries for choline residues present in (lipo)teichoic acids.
authors.affiliation: Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu 9, 28040, Madrid, Spain.
authors.forename: Rubén M
authors.initials: RM
authors.lastname: Buey
authors.forename: Begoña
authors.initials: B
authors.lastname: Monterroso
authors.forename: Margarita
authors.initials: M
authors.lastname: Menéndez
authors.forename: Greg
authors.initials: G
authors.lastname: Diakun
authors.forename: Pablo
authors.initials: P
authors.lastname: Chacón
authors.forename: Juan Antonio
authors.initials: JA
authors.lastname: Hermoso
authors.forename: J Fernando
authors.initials: JF
authors.lastname: Díaz
mesh_terms: D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry*; D020134:Catalytic Domain; D002794:Choline / Q000378:metabolism*; D003460:Crystallization; D004950:Esterases / Q000737:chemistry; D008958:Models, Molecular; D009113:Muramidase / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D053838:Scattering, Small Angle; D013296:Streptococcus pneumoniae / Q000201:enzymology*; D013329:Structure-Activity Relationship; D014461:Ultracentrifugation
chemical_list: D002352:Carrier Proteins; D004950:Esterases; C067928:CPL7 lysozyme; D009113:Muramidase; D002794:Choline