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Proceedings of the 31 st European Peptide SymposiumMichal Lebl, Morten Meldal, Knud J. Jensen, Thomas Hoeg-Jensen (Editors)European Peptide Society, 2010Synthesis of Peptide Analogs of the A2 Subunit(Sequence 558-565) of the Factor FVIIa of Blood CoagulationCharis Anastasopoulos, Yiannis Sarigiannis, andGeorge Stavropoulos*Department of Chemistry, University of Patras, 26500, Patras, GreeceIntroductionIt is known that platelets aggregation causes clotting in the blood vessels during the bloodcirculation due to several reasons. The clots formation is prevented by using anticoagulantdrugs. On the other hand the coagulation of blood is important for maintaining vascularintegrity and thus the precaution of an organism from bleedings and takes place through aprocess of thrombin production. The glycoprotein factor VIII (FVIII) is a key component ofthe fluid phase of the blood coagulation and is comprised of a heavy (A1-A2-B) and a light(A3-C1-C2) peptide chain, which are efficiently cleaved by proteases at three sites, twowithin the heavy and one within the light chain, resulting in alteration of its covalentstructure and conformation [1,2]. This proteolytic cleavage is caused by thrombin or byfactor Xa. Thrombin production is depended on FIXa, which plays a crucial role incurtailing of thrombin generation and accordingly on the additional activation of platelets.Peptides which are expected to inhibit selectively the maximization of thrombin productionare based on the regions in which FVIII interacts with FIX. These both factors are essentialfor normal coagulation and deficiency of either is associated with the bleeding diathesis [3].Results and DiscussionBased upon the acceptance that the sequence loop 558-565:Ser 558 -Val 559 -Asp 560 -Gln 561 -Arg 562 -Gly 563 -Asn 564 -Gln 565of the A2 subunit domain of FVIIIa interacts with FIXa, our research efforts focus on thesynthesis of linear and cyclic head to tail peptides and peptidomimetics, analogs of thissequence, aiming at the inhibition of interaction between FVIIIa and FIXa, in order tosuspend the platelets adhesion and furthermore the thrombin production [4]. All thesynthesized analogs are purified (RP-HPLC) and identified (ESI-MS). We have synthesizedlinear (No 1-3) and cyclic head to tail (No 4) peptides incorporating Asn or Asp (No 3). Inaddition, the analog (No 5) and smaller segments of the same sequence of the A2 subunithave been synthesized by replacement the Gly 563 with NPhe (No 6-8).The synthesized peptide analogs were investigated for their inhibitory activity andtested for clotting deficiency by measuring their activated partial thromboplastin time(APTT) and the reduction of the % value of the FVIIIa that they generate in samplescontaining recombinant FVIIIa, in vitro [5,6].In the first biological assay, control A is poor platelet plasma (PPP) diluted with bufferOwren-Koller in propotion 1:1. In the second one, control A is pure recombinant factorVIIIa and control B is recombinant factor VIIIa diluted with buffer Owren-Koller inpropotion 1:1. The results (Table 1) show clearly that the natural linear peptides (No 1, 2,3) are the most active in the first biological assay. Also No 1 and the cyclic one as well asthe peptidomimetics show increased inhibition of the FVIIIa activity. Specifically the No 5shows activity similar to the natural No 1 in the time delay of APTT.364