Trypsin: Difference between revisions

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== Ligand Binding and Catalysis ==

The structure of this particular bovine trypsin was determined in complex with <scene name='Sandbox_45/Btligand/1'>ligand 10U</scene>, formula '''C'''20'''H'''29'''N'''5'''O'''2, along with two <scene name='Sandbox_45/Btsulfates/1'>sulfate ions</scene>(highlighted) and a Calcium ion (green). Four key amino acids interact with Calcium at a <scene name='Sandbox_45/Lig-metal/1'>subsite loop</scene>. The binding of ligand 10U involves <scene name='Sandbox_45/Ligandwaterbridge/1'>water bridges</scene>, direct <scene name='Sandbox_45/Ligandhbond/1'>hydrogen bonding</scene>, and a host of <scene name='Sandbox_45/Ligandhydrophobic/1'>hydrophobic interactions</scene>. The figure below shows this binding in two dimensions.

The binding of trypsin to ligand 10U somewhat emulates the binding to its specific peptide substrates. The preference for lysine or arginine in trypsin catalysis is due to the composition of the trypsin <scene name='Sandbox_45/Specificitypocketasp189gly216/2'>specificity pocket</scene>. Here (green), Asp 189 and one of two significant glycine backbones, Gly 216, interact with the ligand as they would with Arg or Lys.

[[Image:Ligandinteractionstrypsin.gif|thumb|left|upright=2.5|A two-dimensional representation of trypsin binding Ligand 10U]]

The <scene name='Sandbox_45/Ctriadd102h57s195/4'>catalytic triad</scene>; Asp 102, His 57, and Ser 195, shown here in yellow, is positioned near the substrate. The catalytically active histidine and serine side chains are even near an amide bond in 10U, just like the amide bond broken in peptide hydrolysis. According to FirstGlance in Jmol, there is no bonding of these groups with the ligand, apart from minor van der Waal's interactions with Hist 57. If Ligand 10U were a transition state analog, some covalent connection would exist in addition to hydrogen bonds. 10U simulates the substrate, but does not hydrolyze at either of its two amide bonds, likely due to the local cyclic groups atypical of peptide backbones.

==Regulation==

Trypsin has long been known as unique in that it is an allosterically regulated monomer [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1187220/pdf/biochemj00714-0230a.pdf]. In viewing the 3D structure, the allosteric sight appears to most likely be the subsite loop, which can bind Calcium. New research involving structural comparisons of trypsin-like serine proteases bound and unbound to Calcium and other effectors is being done to better understand the mechanism of this regulation[http://onlinelibrary.wiley.com/doi/10.1002/pro.118/abstract;jsessionid=6685026B895B2DDC831E6A1A30DBA42C.d02t01].

=Catalytic Mechanism=

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@@ Line 10: / Line 10: @@
 <applet load='3ljj' size='350' frame='true' align='right' caption='Trypsin' />
+== Ligand Binding and Catalysis ==
+The structure of this particular bovine trypsin was determined in complex with <scene name='Sandbox_45/Btligand/1'>ligand 10U</scene>, formula '''C'''20'''H'''29'''N'''5'''O'''2, along with two <scene name='Sandbox_45/Btsulfates/1'>sulfate ions</scene>(highlighted) and a Calcium ion (green).  Four key amino acids interact with Calcium at a <scene name='Sandbox_45/Lig-metal/1'>subsite loop</scene>.  The binding of ligand 10U involves <scene name='Sandbox_45/Ligandwaterbridge/1'>water bridges</scene>, direct <scene name='Sandbox_45/Ligandhbond/1'>hydrogen bonding</scene>, and a host of <scene name='Sandbox_45/Ligandhydrophobic/1'>hydrophobic interactions</scene>.  The figure below shows this binding in two dimensions.
+The binding of trypsin to ligand 10U somewhat emulates the binding to its specific peptide substrates.  The preference for lysine or arginine in trypsin catalysis is due to the composition of the trypsin <scene name='Sandbox_45/Specificitypocketasp189gly216/2'>specificity pocket</scene>.  Here (green), Asp 189 and one of two significant glycine backbones, Gly 216, interact with the ligand as they would with Arg or Lys.
+[[Image:Ligandinteractionstrypsin.gif|thumb|left|upright=2.5|A two-dimensional representation of trypsin binding Ligand 10U]]
+The <scene name='Sandbox_45/Ctriadd102h57s195/4'>catalytic triad</scene>; Asp 102, His 57, and Ser 195, shown here in yellow, is positioned near the substrate. The catalytically active histidine and serine side chains are even near an amide bond in 10U, just like the amide bond broken in peptide hydrolysis.  According to FirstGlance in Jmol, there is no bonding of these groups with the ligand, apart from minor van der Waal's interactions with Hist 57.  If Ligand 10U were a transition state analog, some covalent connection would exist in addition to hydrogen bonds. 10U simulates the substrate, but does not hydrolyze at either of its two amide bonds, likely due to the local cyclic groups atypical of peptide backbones.
+==Regulation==
+Trypsin has long been known as unique in that it is an allosterically regulated monomer [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1187220/pdf/biochemj00714-0230a.pdf].  In viewing the 3D structure, the allosteric sight appears to most likely be the subsite loop, which can bind Calcium.  New research involving structural comparisons of trypsin-like serine proteases bound and unbound to Calcium and other effectors is being done to better understand the mechanism of this regulation[http://onlinelibrary.wiley.com/doi/10.1002/pro.118/abstract;jsessionid=6685026B895B2DDC831E6A1A30DBA42C.d02t01].
 =Catalytic Mechanism=