View source for 1ciu

[[Image:1ciu.gif|left|200px]]<br /><applet load="1ciu" size="450" color="white" frame="true" align="right" spinBox="true" 
caption="1ciu, resolution 2.3&Aring;" />
'''THERMOSTABLE CGTASE FROM THERMOANAEROBACTERIUM THERMOSULFURIGENES EM1 AT PH 8.0.'''<br />

==Overview==
The crystal structure of the cyclodextrin glycosyltransferase (CGTase), from the thermophilic microorganism Thermoanaerobacterium, thermosulfurigenes EM1 has been elucidated at 2.3 A resolution. The final, model consists of all 683 amino acid residues, two calcium ions and 343, water molecules, and has a crystallographic R-factor of 17.9% (Rfree, 24.9%) with excellent stereochemistry. The overall fold of the enzyme is, highly similar to that reported for mesophilic CGTases and differences are, observed only at surface loop regions. Closer inspection of these loop, regions and comparison with other CGTase structures reveals that, especially loops 88-95, 335-339 and 534-539 possibly contribute with novel, hydrogen bonds and apolar contacts to the stabilization of the enzyme., Other structural features that might confer thermostability to the T., thermosulfurigenes EM1 CGTase are the introduction of five new, salt-bridges and three Gly to Ala/Pro substitutions. The abundance of Ser, Thr and Tyr residues near the active site and oligosaccharide binding, sites might explain the increased thermostability of CGTase in the, presence of starch, by allowing amylose chains to bind non-specifically to, the protein. Additional stabilization of the A/E domain interface through, apolar contacts involves residues Phe273 and Tyr187. No additional or, improved calcium binding is observed in the structure, suggesting that the, observed stabilization in the presence of calcium ions is caused by the, reduced exchange of calcium from the protein to the solvent, rendering it, less susceptible to unfolding. The 50% decrease in cyclization activity of, the T. thermosulfurigenes EM1 CGTase compared with that of B. circulans, strain 251 appears to be caused by the changes in the conformation and, amino acid composition of the 88-95 loop. In the T. thermosulfurigenes EM1, CGTase there is no residue homologous to Tyr89, which was observed to take, part in stacking interactions with bound substrate in the case of the B., circulans strain 251 CGTase. The lack of this interaction in the, enzyme-substrate complex is expected to destabilize bound substrates prior, to cyclization. Apparently, some catalytic functionality of CGTase has, been sacrificed for the sake of structural stability by modifying loop, regions near the active site.

==About this Structure==
1CIU is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Thermoanaerobacterium_thermosulfurigenes Thermoanaerobacterium thermosulfurigenes] with CA as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/Cyclomaltodextrin_glucanotransferase Cyclomaltodextrin glucanotransferase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=2.4.1.19 2.4.1.19] Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1CIU OCA]. 

==Reference==
Crystal structure at 2.3 A resolution and revised nucleotide sequence of the thermostable cyclodextrin glycosyltransferase from Thermonanaerobacterium thermosulfurigenes EM1., Knegtel RM, Wind RD, Rozeboom HJ, Kalk KH, Buitelaar RM, Dijkhuizen L, Dijkstra BW, J Mol Biol. 1996 Mar 1;256(3):611-22. PMID:[http://ispc.weizmann.ac.il//pmbin/getpm?pmid=8604143 8604143]
[[Category: Cyclomaltodextrin glucanotransferase]]
[[Category: Single protein]]
[[Category: Thermoanaerobacterium thermosulfurigenes]]
[[Category: Dijkstra, B.W.]]
[[Category: Knegtel, R.M.A.]]
[[Category: CA]]
[[Category: thermostable]]

''Page seeded by [http://ispc.weizmann.ac.il/oca OCA ] on Tue Nov 20 12:29:58 2007''