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Page 199<br />

20β-hydroxysteroid dehydrogenase, the root mean square deviation for the two tertiary structures is 2 Å<br />

over 160 C α carbon atoms.<br />

We aligned human 11β-HSD-1 [21] and 11β-HSD-2 [22] with S. hydrogenans 20β-hydroxysteroid<br />

dehydrogenase and Escherichia coli 7α-hydroxysteroid dehydrogenase [37] for 3D modeling. Human<br />

11β-HSD has extra segments at the amino terminus and carboxyl terminus. Previously reported<br />

alignments [30,31,53] were used to find the core structure consisting of about 225 residues that are<br />

structurally similar to the template. The first 190 residues of the 255 residues are reasonably well<br />

conserved among the hydroxysteroid dehydrogenases. Alignment of the C-terminal 65 residues is less<br />

certain as this part contains gaps and insertions. Fortunately, the core 190 residues contains the catalytic<br />

site and the cofactor binding site. We also superimposed the two 11β-HSD structures on mouse carbonyl<br />

reductase [37]. The 11β-HSD 3D structures superimpose nicely on α helices E and F and other helices<br />

and strands that are important in binding of cofactor and substrate. Then, we extracted NADPH from<br />

carbonyl reductase and NAD + from 7α-hydroxysteroid dehydrogenase and inserted the cofactors into<br />

the structures of the two 11β-HSDs.<br />

The α helix F in 17β-HSD-1 [16], 17β-HSD-2 [17], 17β-HSD-3 [18], and porcine 17β-HSD-4 [26] was<br />

constructed <strong>by</strong> modeling on α helix F in 20β-hydroxysteroid dehydrogenase. Comparisons with other<br />

3D structures [33–37] have demonstrated that this α helix is highly conserved. The modeled dimers<br />

were not minimized as a dimer complex to avoid the artifactual adjustment of α helix F side chains.<br />

The Homology program (Biosym Technologies, Inc., 1995) was used to model a 255-residue segment of<br />

11β-HSD and α helix F of 17β-HSD on the S. hydrogenans 20β-hydroxysteroid dehydrogenase<br />

template. To produce the final model (Figures 4 and 5) this program finds an optimal configuration of<br />

the residues when arranged in the template structure <strong>by</strong> minimizing unfavorable interactions between<br />

amino acid side chains. The side chains of each monomer were then minimized (1,000 iterations of the<br />

conjugate gradient) using the Discover program (Biosym Technologies Inc., 1995).<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_199.html [4/5/2004 5:05:34 PM]

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