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==Coagulation Factor XIa==
==Symmetry in the Bcl-Xl interface==  
[[Image:Coag_cartoon.jpg | thumb |350px| Schematic representation of the coagulation response]]
<StructureSection load='2yxj_With_Ligand_Mati_Cohen.pdb' size='500' frame='true' align='right' caption='Bcl-Xl and ABT737 from PDB-ID 2yxj' scene=''>Bcl-Xl is a member of the [http://en.wikipedia.org/wiki/Bcl-2 Bcl-2 family]. This family consists of [http://en.wikipedia.org/wiki/Apoptosis pro-apoptotic] and [http://en.wikipedia.org/wiki/Apoptosis anti-apoptotic] members. Bcl-Xl (in the image)  ,an anti-apoptotic protein, binds pro-apoptotic proteins like BAK and BAD thus regularly inhibit program cell death. Many cancer cells overexpress at least one of the anti-apoptotic members of this family ,thus escaping a needed apoptosis . Therefore, these proteins are important targets for the development of new anti-cancer drugs.
 
The PDB file [[2yxj]] shows the structure of Bcl-Xl and ABT 737. ABT 737 is a potent inhibitor of Bcl-Xl (Kd = 1nM). It binds Bcl-xl in the same position as BAK does as can be seen in [[1bxl]].
==Introduction==
Interestingly the interface of Bcl-Xl is almost symmetric. There are <scene name='43/437742/2yxj_arg/9'>two positively charged residues</scene> Arg 100 and Arg 139.
Factor XIa is unique protease derived from the activation of the coagulation zymogen, factor XI. Factor XIa partcipates in the procoagulant response via contact activation pathway. Synthesized by the liver similar to most vitamin K-dependent coagulation proteins, the zymogen, factor XI circulates in plasma as a 160 kDa disulfide-linked homodimer in complex with high molecular weight kininogen (HK)(REF). Studies show that factor XI is a substrate for various plasma proteins such as  factor XIIa, thrombin, meizothrombin and factor XIa (via autoactivation). Proteolysis of the Arg369-Ile370 bond generates the active enzyme factor XIa which in turn cleaves its substrate factor factor IX to produce the serine protease factor IXa.  
<scene name='43/437742/2yxj_glu/7'>two negatively charged residues</scene> Glu96 and Glu129.
{{STRUCTURE_3bg8 |  PDB=3bg8  |  SCENE=  }}
Two <scene name='43/437742/2yxj_hyd/4'>hydrophobic patches</scene> which include Phe191 Val141 and
 
Ala93 for one, and the other patch includes Phe146 Val126 and Leu108. A look at the <scene name='43/437742/2yxj_space_fill_color_charged/3'>Overall</scene> picture shows that there are hydrophobic patches (in gray) "above" and "below" the ligand ,negatively charged residues "above-right" and "below-left" of the ligand and positively charges on the "right" and "left" of it.
==Protein Structure==
This symmetry can be exploited, a symmetric molecule can bind the same interface in two different ways thus increasing the "chance" of binding which means better binding affinity.
Each dimeric subunit of factor XIa exhibit similar amino acid composition of about 607 residues constituting five main domains. The N-terminus of each subunit contains 4 apple domains (A1, A2, A3 and A4) which are characterized by approximately 90 or 91 amino acid motifs. The C-terminus contain the trypsin-like catalytic domain. Together with Prekallikrein (PK) a monomeric homolog of factor XIa, they belong to the PAN (plasminogen, apple, nematode) module family which all have a conserved N-terminal apple domain.
==Active Site Characteristics==
 
==Recognition of Substrates and Cleavege Mechanism==

Latest revision as of 18:57, 1 September 2013

Symmetry in the Bcl-Xl interface

<StructureSection load='2yxj_With_Ligand_Mati_Cohen.pdb' size='500' frame='true' align='right' caption='Bcl-Xl and ABT737 from PDB-ID 2yxj' scene=>Bcl-Xl is a member of the Bcl-2 family. This family consists of pro-apoptotic and anti-apoptotic members. Bcl-Xl (in the image) ,an anti-apoptotic protein, binds pro-apoptotic proteins like BAK and BAD thus regularly inhibit program cell death. Many cancer cells overexpress at least one of the anti-apoptotic members of this family ,thus escaping a needed apoptosis . Therefore, these proteins are important targets for the development of new anti-cancer drugs. The PDB file 2yxj shows the structure of Bcl-Xl and ABT 737. ABT 737 is a potent inhibitor of Bcl-Xl (Kd = 1nM). It binds Bcl-xl in the same position as BAK does as can be seen in 1bxl. Interestingly the interface of Bcl-Xl is almost symmetric. There are two positively charged residues Arg 100 and Arg 139. two negatively charged residues Glu96 and Glu129. Two hydrophobic patches which include Phe191 Val141 and Ala93 for one, and the other patch includes Phe146 Val126 and Leu108. A look at the Overall picture shows that there are hydrophobic patches (in gray) "above" and "below" the ligand ,negatively charged residues "above-right" and "below-left" of the ligand and positively charges on the "right" and "left" of it. This symmetry can be exploited, a symmetric molecule can bind the same interface in two different ways thus increasing the "chance" of binding which means better binding affinity.