Calcium-induced conformational changes of Thrombospondin-1 signature domain: implications for vascular disease

Abstract

Context: Thrombospondin1 (TSP1) participates in numerous signaling pathways critical for vascular physiology and disease. The conserved signature domain of thrombospondin 1 (TSP1-Sig1) comprises three epidermal growth factor (EGF), 13 calcium-binding type 3 thrombospondin (T3) repeats, and one lectin-like module arranged in a stalk-wire-globe topology. TSP1 is known to be present in both calcium-replete (Holo-) and calcium-depleted (Apo-) state, each with distinct downstream signaling effects.

Objective: To prepare a homology model of TSP1-Sig1 and investigate the effect of calcium on its dynamic structure and interactions.

Methods: A homology model of Holo-TSP1-Sig1 was prepared with TSP2 as template in Swissmodel workspace. The Apo-form of the model was obtained by omitting the bound calcium ions from the homology model. Molecular dynamics (MD) simulation studies (100 ns) were performed on the Holo- and Apo- forms of TSP1 using Gromacs4.6.5.

Results and discussion: After simulation, Holo-TSP1-Sig1 showed significant reorientation at the interface of the EGF1-2 and EGF2-3 modules. The T3 wire is predicted to show the maximum mobility and deviation from the initial model. In Apo-TSP1-Sig1 model, the T3 repeats unfolded and formed coils with predicted increase in flexibility. Apo-TSP1-Sig1model also predicted the exposure of the binding sites for neutrophil elastase, integrin and fibroblast growth factor 2. We present a structural model and hypothesis for the role of TSP1-Sig1 interactions in the development of vascular disorders.

Conclusion: The simulated model of the fully calcium-loaded and calcium-depleted TSP1-Sig1 may enable the development of its interactions as a novel therapeutic target for the treatment of vascular diseases.

Keywords:

• Thrombospondin-1 signature domain
• homology modeling
• molecular dynamics simulation
• calcium ions
• vascular disease

Acknowledgements

We acknowledge Bioinformatics Resources and Applications Facility (BRAF), CDAC, Pune for the use of PARAM Biochrome facility and ShivNadar University (SNU), UP for the Magus high performance computational facility for running the MD simulations.

Disclosure statement

The authors report no declarations of interest.

Funding

AG acknowledges financial support from Netaji Subhas Institute of Technology.