X-RAY STRUCTURE OF CYCLODEXTRIN GLUCANOTRANSFERASE FROM ALKALOPHILIC BACILLUS SP-1011 - COMPARISON OF 2 INDEPENDENT MOLECULES AT 1.8-ANGSTROM RESOLUTION

Citation
K. Harata et al., X-RAY STRUCTURE OF CYCLODEXTRIN GLUCANOTRANSFERASE FROM ALKALOPHILIC BACILLUS SP-1011 - COMPARISON OF 2 INDEPENDENT MOLECULES AT 1.8-ANGSTROM RESOLUTION, Acta crystallographica. Section D, Biological crystallography, 52, 1996, pp. 1136-1145
Citations number
22
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Crystallography,"Biochemical Research Methods",Biology
ISSN journal
0907-4449
Volume
52
Year of publication
1996
Part
6
Pages
1136 - 1145
Database
ISI
SICI code
0907-4449(1996)52:<1136:XSOCGF>2.0.ZU;2-J
Abstract
Cyclodextrin glucanotransferase (CGTase) is an enzyme which produces c yclodextrins by the degradation of starch. The enzyme from alkalophili c Bacillus sp. 1011, consisting of 686 amino acid residues, was crysta llized from the solution containing 20% PEG 3000 and 20% 2-propanol at pH 5.6 adjusted with citrate buffer, The space group was P1 and the u nit cell contained two molecules (V-m = 2.41 Angstrom(3) Da(-1)). The structure was solved by the molecular replacement method and refined t o a conventional R value of 0.161 (R(free) = 0.211) for the reflection s in the resolution range 1.8-10 Angstrom by energy minimization combi ned with simulated annealing. The molecule consists of five domains, d esignated A-E, and its backbone structure is similar to the structure of other bacterial CGTases. The molecule has two calcium binding sites where calcium ions are coordinated by seven ligands, forming a distor ted pentagonal bipyramid. The two independent molecules are related by a pseudotwofold symmetry and are superimposed with an r.m,s, deviatio n value of 0.32 Angstrom for equivalent C-alpha atoms. Comparison of t hese molecules indicated the relatively large mobility of domains C an d E with respect to domain A, The active site is filled with water mol ecules forming a hydrogen-bond network with polar side-chain groups. T wo water molecules commonly found in the active center of both molecul es link to several catalytically important residues by hydrogen bonds and participate in maintaining a similar orientation of side chains in the two independent molecules.