Key result
Deleting the S100A4 C-terminus increases Ca2+ binding affinity ~40-fold, revealing an autoinhibitory domain.
Why the study?
The role of the C-terminal random coil region in tuning the Ca2+-binding affinity and conformational activation of S100A4 was not fully understood.
The C-terminal random coil of S100A4 acts as a conformational switch upon Ca2+ binding, tuning its affinity and potentially mediating protein-protein interactions.
C-terminal deletion alters Ca2+-dependent S100A4 scattering; leaves open its role in metastasis pending functional validation.
S100A4 interacts with many binding partners upon Ca2+ activation and is strongly associated with increased metastasis formation. In order to understand the role of the C-terminal random coil for the protein function we examined how small angle X-ray scattering of the wild-type S100A4 and its C-terminal deletion mutant (residues 1-88, Δ13) changes upon Ca2+ binding. We found that the scattering intensity of wild-type S100A4 changes substantially in the 0.15-0.25 Å-1 q-range whereas a similar change is not visible in the C-terminus deleted mutant. Ensemble optimization SAXS modeling indicates that the entire C-terminus is extended when Ca2+ is bound. Pulsed field gradient NMR measurements provide further support as the hydrodynamic radius in the wild-type protein increases upon Ca2+ binding while the radius of Δ13 mutant does not change. Molecular dynamics simulations provide a rational explanation of the structural transition: the positively charged C-terminal residues associate with the negatively charged residues of the Ca2+-free EF-hands and these interactions loosen up considerably upon Ca2+-binding. As a consequence the Δ13 mutant has increased Ca2+ affinity and is constantly loaded at Ca2+ concentration ranges typically present in cells. The activation of the entire C-terminal random coil may play a role in mediating interaction with selected partner proteins of S100A4.
No takes yet. Share an insight, caveat, or question.
Duelli et al. (2014) studied this question. C-terminal deletion (D13 mutant) of S100A4 vs. Wild-type S100A4 was evaluated on Ca2+-binding affinity and conformational changes. Deletion of the C-terminal random coil region of S100A4 increased its Ca2+ binding affinity by forty-fold compared to the wild-type protein, indicating the C-terminus acts as an autoinhibitory domain.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: