Sandbox Reserved 895: Difference between revisions
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Using the crystal structure of bovine RPE65 (PDB: ''3FSN''), which is about 99% similar to human RPE65, (although the crystal structure for human RPE65 is not currently available) as the basis of studying the RPE65 structure, RPE65 resembles a seven-bladed β-propeller with single-stranded extension on blades VI and VII and two-stranded extension on blade III shown in '''Figure 4A'''. The top face of the β-propeller is defined by connecting the outer strand of the β-sheet with the inner strand of the next β-sheet as shown in '''Figure 4B'''. The iron cofactor is located near the top surface of the propeller which is coordinated by four His residues and three secondary Glu residues. Each blade of the propeller contributes one His residue to coordinate with the iron ion. A hydrophobic tunnel leads from the protein exterior to the active site which is defined by the iron ion to accommodate the passage of retinoids (which are conjugated to a fatty acid tail) from the membrane to the RPE65 catalytic site shown in '''Figure 4C'''. The mouth of the tunnel is surrounded by three groups of nonpolar residues (169-202, 234-236 and 261-271) that contribute to the overall hydrophobicity of the tunnel and the integration with the lipid bilayer. There are also a few aromatic amino acid side chains that reside in this portion of the enzyme. This suggest that the depth of the RPE65 membrane is restricted to the proximal portions of the phospholipid acyl chains with respect to the polar head groups. Arg and Lys residues within this region also contribute to the association with the negatively charged phospholipid head groups. Using a helical wheel plot, Kiser and colleagues were able to determine that the tunnel region of RPE65 is amphipathic with positive charged residues separating the hydrophobic face from the hydrophilic face as shown in '''Figure 4C'''. <ref> DOI 19805034 </ref> | Using the crystal structure of bovine RPE65 (PDB: ''3FSN''), which is about 99% similar to human RPE65, (although the crystal structure for human RPE65 is not currently available) as the basis of studying the RPE65 structure, RPE65 resembles a seven-bladed β-propeller with single-stranded extension on blades VI and VII and two-stranded extension on blade III shown in '''Figure 4A'''. The top face of the β-propeller is defined by connecting the outer strand of the β-sheet with the inner strand of the next β-sheet as shown in '''Figure 4B'''. The iron cofactor is located near the top surface of the propeller which is coordinated by four His residues and three secondary Glu residues. Each blade of the propeller contributes one His residue to coordinate with the iron ion. A hydrophobic tunnel leads from the protein exterior to the active site which is defined by the iron ion to accommodate the passage of retinoids (which are conjugated to a fatty acid tail) from the membrane to the RPE65 catalytic site shown in '''Figure 4C'''. The mouth of the tunnel is surrounded by three groups of nonpolar residues (169-202, 234-236 and 261-271) that contribute to the overall hydrophobicity of the tunnel and the integration with the lipid bilayer. There are also a few aromatic amino acid side chains that reside in this portion of the enzyme. This suggest that the depth of the RPE65 membrane is restricted to the proximal portions of the phospholipid acyl chains with respect to the polar head groups. Arg and Lys residues within this region also contribute to the association with the negatively charged phospholipid head groups. Using a helical wheel plot, Kiser and colleagues were able to determine that the tunnel region of RPE65 is amphipathic with positive charged residues separating the hydrophobic face from the hydrophilic face as shown in '''Figure 4C'''. <ref> DOI 19805034 </ref> | ||
[[Image:RPE65_Figure4_Structure.jpg|thumb|center|512 px|alt=Figure 4: RPE65 structure| '''Figure 4:''' | [[Image:RPE65_Figure4_Structure.jpg|thumb|center|512 px|alt=Figure 4: RPE65 structure| '''Figure 4:''' Crystal structure of bovine RPE65 (A) RPE65 monomer viewed from the bottom face of the seven-bladed β-propeller labeled in roman numerals from I to VII (B) Topology diagram of RPE65 showing the key amino acid residues that interact with the iron ion (C) Proposed membrane-binding surface of RPE65 with the hypothesized entry and exit tunnel (shown in blue mesh). The hydrophobic residues (colored in orange) that are likely responsible for the anchoring of RPE65 to the membrane. (Insert) Helical wheel plot showing possible amphipathic α-helix configuration under appropraite conditions. <ref> DOI 19805034 </ref>]] | ||
==== '''[1.2.2.2] Active Site Structural Analysis of RPE65''' ==== | ==== '''[1.2.2.2] Active Site Structural Analysis of RPE65''' ==== | ||
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Drastic accumulation of lipofuscin in the hRPE is a hallmark sign of juvenile-onset macular dystrophy also known as Stargardt’s Disease. It is suggested that retinoid cycle modulation can help prevent the drastic accumulation of lipofuscin leading to the development of Stargardt’s Disease. Currently in the United States, the use of (R)-emixustat is being tested in phase III clinical trails. <ref> DOI 24056528 </ref> | Drastic accumulation of lipofuscin in the hRPE is a hallmark sign of juvenile-onset macular dystrophy also known as Stargardt’s Disease. It is suggested that retinoid cycle modulation can help prevent the drastic accumulation of lipofuscin leading to the development of Stargardt’s Disease. Currently in the United States, the use of (R)-emixustat is being tested in phase III clinical trails. <ref> DOI 24056528 </ref> | ||
= References = | = '''[4] References''' = | ||
<references/> | <references/> | ||
