Ketosteroid Isomerase: Difference between revisions
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The biologically active unit of KSI is a 2-fold symmetric dimer in which the two chains are packed together via hydrophobic and electrostatic interactions between the "back faces" of the β-sheets. The curved β-sheets on each of the monomers expose convex faces to each other, forming well-defined interactions. In their NMR structure of KSI, Massiah et al. identified interchain hydrophobic interactions (A), as well, a number of polar residues (B) located within the dimer interface. Although they were unable to resolve interchain hydrogen-bonding interactions, they were able to resolve an intrachain hydrogen bond between His100 and Glu77 (C). The apparent pKa of His100 is 4.3, and the authors speculate that this unusually low pKa may be the result of electrostatic effects from nearby cationic residues (Arg102 and Arg113). | The biologically active unit of KSI is a 2-fold symmetric dimer in which the two chains are packed together via hydrophobic and electrostatic interactions between the "back faces" of the β-sheets. The curved β-sheets on each of the monomers expose convex faces to each other, forming well-defined interactions. In their NMR structure of KSI, Massiah et al. identified interchain hydrophobic interactions (A), as well, a number of polar residues (B) located within the dimer interface. Although they were unable to resolve interchain hydrogen-bonding interactions, they were able to resolve an intrachain hydrogen bond between His100 and Glu77 (C). The apparent pKa of His100 is 4.3, and the authors speculate that this unusually low pKa may be the result of electrostatic effects from nearby cationic residues (Arg102 and Arg113). | ||
[[Image: | [[Image:dimer_interface.png|center|'''Interactions at KSI's dimer interface''' (A) Hydrophobic residues. (B) Hydrophillic residues.]] | ||
In their X-ray crystal structure of KSI, Kim et al. identified bound water molecules within the dimer interface which may mediate hydrogen-bonds between Thr68, Arg72, and Asp96. The water mediated hydrogen bond between Thr68 and Arg72 is illustrated below. Kim et al. also identified interchain hydrogen bonds between the backbone carbonyl oxygens of Val71, Ala73, and Val97. | In their X-ray crystal structure of KSI, Kim et al. identified bound water molecules within the dimer interface which may mediate hydrogen-bonds between Thr68, Arg72, and Asp96. The water mediated hydrogen bond between Thr68 and Arg72 is illustrated below. Kim et al. also identified interchain hydrogen bonds between the backbone carbonyl oxygens of Val71, Ala73, and Val97. | ||
