Sandbox Reserved 1475: Difference between revisions

In [[Figure 3]] it is possible to see the active site, which is where the substrate interacts with Cys-302. The Cys-302 residue acts as a nucleophilic active site on each domain as a hydrogen-bond turn that is enclosed deep inside the substrate access channel. This is where the large substrate molecules can gain access to the catalytic Cys-302. The side chain of Cys-302 is the nucleophile that attaches to the substrate retinol (at its carbonyl) when it is deprotonated. To get Cys-302 deprotonated, the amino acid Glu-268 is needed as the proton acceptor. The amine backbone of Glu-268 helps stabilize the negatively charged transition state, which helps the enzyme result in an energetically favorable conformation. Asn-187 is also used as a transition site stabilizer and is on all four domains. It worked in a similar fashion as Glu-268, in that Asn-187 amine backbone is used to stabilize the negatively charged transition state. <ref name="Analysis of Catalytic Residues in Enzyme Active Sites">J Mol Biol 324:105-121 </ref>