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.

FhCaBP2: a Fasciola hepatica calcium-binding protein with EF-hand and dynein light chain domains

“…Both domains of the protein are involved in dimerization: the EF-hand domain and the DLC-like domain can both be cross-linked under similar conditions to the full length protein. This contrasts with FhCaBP3 and FhCaBP4 which homodimerize in a calcium sensitive manner, but is similar to the S. mansoni proteins SmTAL1 and SmTAL2 which form calcium-insensitive homodimers (Orr et al 2012;Banford et al 2013;Thomas et al 2015). However, cross-linking of the DLC-like domain was not greatly affected by the presence or absence of calcium or manganese ions (Fig.…”

“…The protein also interacts with manganese ions, a common feature with FhCaBP3 and FhCaBP4 and some members of the S. mansoni TAL family proteins (Orr et al 2012;Banford et al 2013;Thomas et al 2015). The protein also interacts with manganese ions, a common feature with FhCaBP3 and FhCaBP4 and some members of the S. mansoni TAL family proteins (Orr et al 2012;Banford et al 2013;Thomas et al 2015).…”

“…Of the family members characterized to date, it is functionally most similar to FhCaBP3 (Orr et al 2012;Banford et al 2013;Thomas et al 2015). It differs in its ion-binding properties and its response to ions to some other family members.…”

Molecular and Structural Characterization of the Tegumental 20.6-kDa Protein in Clonorchis sinensis as a Potential Druggable Target

“…This region can decrease the quality of the overall model, as it requires additional simulation time, and it interferes with the structural clustering process [25]. These regions have been predicted representing tegumental protein linkers because they lack secondary structure in Schistosoma mansoni [26] and Fasciola hepatica [27]. To address this issue, we split the whole sequence into two domains, domain 1 (aa1–74) and domain 2 (aa75–175), based on the disordered region rather than removing the region.…”

“…DLC-containing proteins can form homodimers through hydrogen bonds, backbone-side chain electrostatic interactions and van der Waals contacts between side chains [43]. Previous studies have indicated that the homodimeric DLCs in S. mansoni [26] and F. hepatica [27] were composed of two asymmetric monomers through β-sheet interactions. The homodimer of CsTegu20.6 was constructed using GalaxyGemini [44] with only the C chain of DLC1 (PDB ID: 4DS1_C), although the fifth β-strand (indicated with a dotted circles) as a monomeric counterpart was missed in the predicted structure [45] (Figure 5C).…”