Sandbox Reserved 770: Difference between revisions

Line 74:

[[Image:PAL_CIN_Interactions.png|right|thumb|Figure 8. Lysine468 attachment to carboxyl group of substrate]]

[[Image:Stabilizing_residues_of_PAL_active_site.png|thumb|left|Figure 7. Lys468 residue always adjacent to Gly residue]]

[[Image:Ten_PAL.gif|thumb|left|~~Figure9~~. Overlay of ten PAL active sites. The active sites are centered on the MIO−NH2 complex.]]

[[Image:Ten_PAL.gif|thumb|left|Figure 9. Overlay of ten PAL active sites. The active sites are centered on the MIO−NH2 complex.]]

'''Lysine468'''

The positively charged side chain of Lys468 recognizes the carboxyl group of substrate by forming a salt bridge, when it is located in the mouth of the funnel. Before the side chain encloses, Lysine chaperones the substrate to its reactive position for sharing additional interactions between substrate's carboxyl group (Figure 8) and side chains Glu496 and Gln500. Lys468 is strictly conserved with almost always adjacent Gly residue (Figure 7), which would improve mobility of Lys486 chaperone ability for substrate. Lys486 also acts to place the NH2 group of the substrate near MIO to ensure the carboxylate group of substrate does not react nonproductively with methylidene of MIO by forming an ester.

'''Histidine137'''

Formation of carbanion intermediate is promoted by the positioning of the NH2 group of Asn270 to share a hydrogen bond with the enolate oxygen of MIO, increasing the electropositivity of MIO methylidene group. Abstraction of the pro-''S'' hydrogen from C3 of substrate to form product ''trans''-cinnamic acid is catalyzed by His137 residue on helix one, which is connected to loop regions on both its C and N termini, allowing for its movement. His137 is located near the C terminus with its negative pole directed toward the active site, thus increasing basicity of His137 so it can act as a base. Development and further stabilization of the carbanion are provided by the phenyl group of the substrate, helix dipoles directing positive poles toward residues, improved MIO electron-withdrawing capability (enhanced by positive poles of three alpha helices), and electron withdrawal from substrates carboxy group by residues of positive pole N termini in alpha helices. MIO group assists in the breakage of C-N bond of substrate to proceed carbanion intermediate to product ''trans''-cinnamate. Once C-N bond is broken by PAL, cinnamate leaves the active site by Lys468 chaperone.

Formation of carbanion intermediate is promoted by the positioning of the NH2 group of Asn270 to share a hydrogen bond with the enolate oxygen of MIO, increasing the electropositivity of MIO methylidene group, shown in Figure 9. Abstraction of the pro-''S'' hydrogen from C3 of substrate to form product ''trans''-cinnamic acid is catalyzed by His137 residue on helix one, which is connected to loop regions on both its C and N termini, allowing for its movement. His137 is located near the C terminus with its negative pole directed toward the active site, thus increasing basicity of His137 so it can act as a base. Development and further stabilization of the carbanion are provided by the phenyl group of the substrate, helix dipoles directing positive poles toward residues, improved MIO electron-withdrawing capability (enhanced by positive poles of three alpha helices), and electron withdrawal from substrates carboxy group by residues of positive pole N termini in alpha helices. MIO group assists in the breakage of C-N bond of substrate to proceed carbanion intermediate to product ''trans''-cinnamate. Once C-N bond is broken by PAL, cinnamate leaves the active site by Lys468 chaperone.

==References==

Sandbox Reserved 770: Difference between revisions

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@@ Line 74: / Line 74: @@
 [[Image:PAL_CIN_Interactions.png|right|thumb|Figure 8. Lysine468 attachment to carboxyl group of substrate]]
 [[Image:Stabilizing_residues_of_PAL_active_site.png|thumb|left|Figure 7. Lys468 residue always adjacent to Gly residue]]
-[[Image:Ten_PAL.gif|thumb|left|Figure9. Overlay of ten PAL active sites. The active sites are centered on the MIO−NH2 complex.]]
+[[Image:Ten_PAL.gif|thumb|left|Figure 9. Overlay of ten PAL active sites. The active sites are centered on the MIO−NH2 complex.]]
 '''Lysine468'''
 The positively charged side chain of Lys468 recognizes the carboxyl group of substrate by forming a salt bridge, when it is located in the mouth of the funnel. Before the side chain encloses, Lysine chaperones the substrate to its reactive position for sharing additional interactions between substrate's carboxyl group (Figure 8) and side chains Glu496 and Gln500. Lys468 is strictly conserved with almost always adjacent Gly residue (Figure 7), which would improve mobility of Lys486 chaperone ability for substrate. Lys486 also acts to place the NH2 group of the substrate near MIO to ensure the carboxylate group of substrate does not react nonproductively with methylidene of MIO by forming an ester.
 '''Histidine137'''
-Formation of carbanion intermediate is promoted by the positioning of the NH2 group of Asn270 to share a hydrogen bond with the enolate oxygen of MIO, increasing the electropositivity of MIO methylidene group. Abstraction of the pro-''S'' hydrogen from C3 of substrate to form product ''trans''-cinnamic acid is catalyzed by His137 residue on helix one, which is connected to loop regions on both its C and N termini, allowing for its movement. His137 is located near the C terminus with its negative pole directed toward the active site, thus increasing basicity of His137 so it can act as a base. Development and further stabilization of the carbanion are provided by the phenyl group of the substrate, helix dipoles directing positive poles toward residues, improved MIO electron-withdrawing capability (enhanced by positive poles of three alpha helices), and electron withdrawal from substrates carboxy group by residues of positive pole N termini in alpha helices. MIO group assists in the breakage of C-N bond of substrate to proceed carbanion intermediate to product ''trans''-cinnamate. Once C-N bond is broken by PAL, cinnamate leaves the active site by Lys468 chaperone.
+Formation of carbanion intermediate is promoted by the positioning of the NH2 group of Asn270 to share a hydrogen bond with the enolate oxygen of MIO, increasing the electropositivity of MIO methylidene group, shown in Figure 9. Abstraction of the pro-''S'' hydrogen from C3 of substrate to form product ''trans''-cinnamic acid is catalyzed by His137 residue on helix one, which is connected to loop regions on both its C and N termini, allowing for its movement. His137 is located near the C terminus with its negative pole directed toward the active site, thus increasing basicity of His137 so it can act as a base. Development and further stabilization of the carbanion are provided by the phenyl group of the substrate, helix dipoles directing positive poles toward residues, improved MIO electron-withdrawing capability (enhanced by positive poles of three alpha helices), and electron withdrawal from substrates carboxy group by residues of positive pole N termini in alpha helices. MIO group assists in the breakage of C-N bond of substrate to proceed carbanion intermediate to product ''trans''-cinnamate. Once C-N bond is broken by PAL, cinnamate leaves the active site by Lys468 chaperone.
 ==References==
 <references />