Factor IX: Difference between revisions

<scene name='Factor_IX/Ixstructure_egf1/2'>EGF-1</scene> and <scene name='Factor_IX/Ixstructure_egf2/2'>EGF-2</scene>). The N-terminus of <scene name='Factor_IX/Ixstructure_egf1/2'>EGF-1</scene> contains a Ca2+ binding site, while the C-terminus connects to a hydrophobic pocket of <scene name='Factor_IX/Ixstructure_egf2/2'>EGF-2</scene> by a salt bridge through Lys122 (<scene name='Factor_IX/Ixstructure_egf1/2'>EGF-1</scene> residue) and Gln74 (<scene name='Factor_IX/Ixstructure_egf2/2'>EGF-2</scene>)<ref>PMID:11723140</ref>. <scene name='Factor_IX/Ixstructure_egf2/2'>EGF-2</scene> connects to the <scene name='Factor_IX/Ixstructure_chainc/2'>serine protease</scene> domain through a linker peptide that is required for a proper orientation and folding of <scene name='Factor_IX/Ixstructure_chainc/2'>serine proteases</scene>. To have a physiologically active factor IX, two cleaveges must occur to remove a 35 amino acid region that precedes the catalytic region.  

The first cleave is at Arg145, generating an inactive FIXα. The second cleavage is at Arg180 results in a catalytically active molecule FIXaβ. This resulting heterodimer is held by a disulfide bridge at Cys132-Cys289. The <scene name='Factor_IX/Ixstructure_chainc/2'>serine protease</scene>  contains a catalytic triad of <scene name='Factor_IX/Ixstructure_catalytictriad/2'>His221, Asp269, and Ser365</scene><ref>PMID:9374470</ref>. Upon cleave at Arg180, Val181 can form a salt bridge with Asp364, which is a characteristic of active <scene name='Factor_IX/Ixstructure_chainc/2'>serine proteases</scene>. The active FIXa, can then interact with its cofactor, FVIIIa, to form a membrane-bound Xase complex, which activated FX to FXa.

== Gene Structure and Expression: ==

The gene for factor IX is located on the long arm of chromosome X between positions 26.3- and 27.1 and contains eight exons and seven introns, which segregate the FIX gene into specific structural regions.