Designing an In-Silico Mimetic for Thrombopoietin Using Combinatorial Library

Abstract: Differentiation and proliferation of megakaryocytic progenitor cells into mature platelets is triggered and activated upon binding of Thrombopoietin Receptor (TPOR), a cytokine receptor protein, to thrombopoietin (TPO), a 95 KD glycoprotein hormone. TPO plays a very important role as it can easily direct Hematopoietic Progenitor Cells into the megakaryocytic lineage but even then very few mimetic have been reported, Agonists such as Romiplostim and Electrombopag are reported, recombinant TPO mimetic are also available but structural mimetic is only TMP, so the scope of further research is available. A promising approach for designing a mimetic can be targeting the binding site of the receptor such that the mimetic peptide has similar agonist activity as the ligand. Diverse libraries can be created using in-silico approaches and they are analyzed to bind receptor efficiently. In this study efforts are made for the development of TPO mimetic with therapeutic potential. TPO increases its number, prevent apoptosis, and thereby increases platelet production. Activation of TPO receptor leads to phosphorylation of the cytoplasmic domain as well as downstream activation of JAK2, STAT5, and other anti-apoptotic pathways. This increases the viability of stem cells and precursors of all lineages. The anti-apoptotic effect of TPO is probably important in patients with ITP bone marrow megakaryocytes and megakaryocyte precursors are already increased but these cells are undergoing apoptosis mediated by anti-platelet IgG and T cells, thereby limiting platelet production. Administration of TPO decreases the apoptotic rate of the megakaryocyte precursors and thereby enhance the platelet production. Once produced, platelets are still affected by TPO. TPOs new Combinatorial library was designed by interaction sites of TPOR with TPO and previously reported TPO mimetic peptide (TMP), further screening of combinatorial library was done and an efficient mimetic was chosen based on scoring function commonly called Energy. Energy is calculated in terms of KJ/mol, based on the orientations generated by docking ligand with the receptor, the most efficient ligand has the most stable conformation with minimum energy value. In this study docking of TPO and TPOR has a minimum energy value of -518.20, TPOR and mimetic designed has a total score of -456.55which is better than the known mimetic TMP, which has an energy score of -170.17 with TPOR. Computational approaches confirmed that the resulting peptide mimetic was stable and similar in nature to TPO. Further Ex-vivo study of designed mimetic can confirm its role in regenerative medicine, increasing the shelf life of platelet to improve cellular viability of platelet by preventing programmed cell death, i. e. apoptosis, which can be achieved by adding TPO during storage since TPO levels increase when platelet count is low, to stimulate additional production. TPO is absorbed by transfused platelets, which may decrease available TPO level or in the disease condition.

Keywords: Thrombopoietin, Thrombopoietin receptor, Mimetic, Library designing, Docking

Edition: Volume 5 Issue 4, April 2016,

Pages: 2426 - 2432