Ketosteroid Isomerase: Difference between revisions
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β-strand 1 is connected to β-strand 2 via a <scene name='User:Laura_M._Haynes/Sandbox_1/Cis_loop/1'>four residue linkage</scene> (Pro39 to Ser42) with Pro39 being in a cis-conformation. Two examples of [http://en.wikipedia.org/wiki/Turn_%28biochemistry%29 type-II β-turns] can also be observed in KSI-between β-stands 3 & 4 (<scene name='User:Laura_M._Haynes/Sandbox_1/Turn_1/1'>Ala75-Asn76→see figure</scene>) and β-strands 4 & 5 (<scene name='User:Laura_M._Haynes/Sandbox_1/Turn_2/1'>Gln89-Gly90</scene>). A loop structure (<scene name='User:Laura_M._Haynes/Sandbox_1/Loop2/1'>Asn105-Val107</scene>) also connects β-strands 5 and 6. | β-strand 1 is connected to β-strand 2 via a <scene name='User:Laura_M._Haynes/Sandbox_1/Cis_loop/1'>four residue linkage</scene> (Pro39 to Ser42) with Pro39 being in a cis-conformation. Two examples of [http://en.wikipedia.org/wiki/Turn_%28biochemistry%29 type-II β-turns] can also be observed in KSI-between β-stands 3 & 4 (<scene name='User:Laura_M._Haynes/Sandbox_1/Turn_1/1'>Ala75-Asn76→see figure</scene>) and β-strands 4 & 5 (<scene name='User:Laura_M._Haynes/Sandbox_1/Turn_2/1'>Gln89-Gly90</scene>). A loop structure (<scene name='User:Laura_M._Haynes/Sandbox_1/Loop2/1'>Asn105-Val107</scene>) also connects β-strands 5 and 6. | ||
===Dimer Interface=== | ===Dimer Interface=== | ||
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. | 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. | ||
[[Image:dimer_interface.png|thumb| | [[Image:dimer_interface.png|thumb|left|760px|'''Interactions at KSI's dimer interface''' (A) Hydrophobic residues. (B) Hydrophillic residues.]][[Image:Kim1.png|thumb|right|250px|'''Water mediated dimer interaction between Thr68 and Arg72.''' ]] | ||
In their X-ray crystal structure of KSI, Kim et al.<ref name="1OHO">PMID:9369474 </ref> 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 possibe interchain hydrogen bonds between the backbone carbonyl oxygens of Val71, Ala73, and Val97 with the side chains of Asn120, Ser117, and Arg72 respectively based on the solution structure of Wu et al.<ref name="Wu" /> | |||
===Hydrophobic Active Site=== | ===Hydrophobic Active Site=== | ||
