title: Comparative biochemical analysis of three members of the Schistosoma mansoni TAL family: Differences in ion and drug binding properties.
abstract: The tegumental allergen-like (TAL) proteins from Schistosoma mansoni are part of a family of calcium binding proteins found only in parasitic flatworms. These proteins have attracted interest as potential drug or vaccine targets, yet comparatively little is known about their biochemistry. Here, we compared the biochemical properties of three members of this family: SmTAL1 (Sm22.6), SmTAL2 (Sm21.7) and SmTAL3 (Sm20.8). Molecular modelling suggested that, despite similarities in domain organisation, there are differences in the three proteins' structures. SmTAL1 was predicted to have two functional calcium binding sites and SmTAL2 was predicted to have one. Despite the presence of two EF-hand-like structures in SmTAL3, neither was predicted to be functional. These predictions were confirmed by native gel electrophoresis, intrinsic fluorescence and differential scanning fluorimetry: both SmTAL1 and SmTAL2 are able to bind calcium ions reversibly, but SmTAL3 is not. SmTAL1 is also able to interact with manganese, strontium, iron(II) and nickel ions. SmTAL2 has a different ion binding profile interacting with cadmium, manganese, magnesium, strontium and barium ions in addition to calcium. All three proteins form dimers and, in contrast to some Fasciola hepatica proteins from the same family; dimerization is not affected by calcium ions. SmTAL1 interacts with the anti-schistosomal drug praziquantel and the calmodulin antagonists trifluoperazine, chlorpromazine and W7. SmTAL2 interacts only with W7. SmTAL3 interacts with the aforementioned calmodulin antagonists and thiamylal, but not praziquantel. Overall, these data suggest that the proteins have different biochemical properties and thus, most likely, different in vivo functions.
authors.affiliation: School of Biological Sciences, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast, BT9 7BL, UK; Institute for Global Food Security, Queen's University Belfast, 18-30 Malone Road, Belfast, BT9 5BN, UK.
authors.forename: Charlotte M
authors.initials: CM
authors.lastname: Thomas
authors.affiliation: Department of Pathology, University of Cambridge, Cambridge, CB2 1QP, UK.
authors.forename: Colin M
authors.initials: CM
authors.lastname: Fitzsimmons
authors.affiliation: Department of Pathology, University of Cambridge, Cambridge, CB2 1QP, UK.
authors.forename: David W
authors.initials: DW
authors.lastname: Dunne
authors.affiliation: School of Biological Sciences, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast, BT9 7BL, UK; Institute for Global Food Security, Queen's University Belfast, 18-30 Malone Road, Belfast, BT9 5BN, UK. Electronic address: d.timson@qub.ac.uk.
authors.forename: David J
authors.initials: DJ
authors.lastname: Timson
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D015801:Helminth Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D012550:Schistosoma mansoni; D013045:Species Specificity
chemical_list: D015801:Helminth Proteins; D004364:Pharmaceutical Preparations; D002118:Calcium
keywords: Calcium binding protein; EF-hand protein; Praziquantel; Schistosomiasis; Tegumental allergen