PDBsum entry 1cem

Glycosyltransferase

PDB id: 1cem

Contents

Protein chain

363 a.a.

Waters ×266

References listed in PDB file

Key reference

Title

The crystal structure of endoglucanase cela, A family 8 glycosyl hydrolase from clostridium thermocellum.

Authors

P.M.Alzari, H.Souchon, R.Dominguez.

Ref.

Structure, 1996, 4, 265-275. [DOI no: 10.1016/S0969-2126(96)00031-7]

PubMed id

8805535

Abstract

BACKGROUND: Cellulases, which catalyze the hydrolysis of glycosidic bonds in cellulose, can be classified into several different protein families. Endoglucanase CelA is a member of glycosyl hydrolase family 8, a family for which no structural information was previously available. RESULTS: The crystal structure of CelA was determined by multiple isomorphous replacement and refined to 1.65 A resolution. The protein folds into a regular (alpha/alpha)6 barrel formed by six inner and six outer alpha helices. Cello-oligosaccharides bind to an acidic cleft containing at least five D-glucosyl-binding subsites (A-E) such that the scissile glycosidic linkage lies between subsites C and D. The strictly conserved residue Glu95, which occupies the center of the substrate-binding cleft and is hydrogen bonded to the glycosidic oxygen, has been assigned the catalytic role of proton donor. CONCLUSIONS: The present analysis provides a basis for modeling homologous family 8 cellulases. The architecture of the active-site cleft, presenting at least five glucosyl-binding subsites, explains why family 8 cellulases cleave cello-oligosaccharide polymers that are at least five D-glycosyl subunits long. Furthermore, the structure of CelA allows comparison with (alpha/alpha)6 barrel glycosidases that are not related in sequence, suggesting a possible, albeit distant, evolutionary relationship between different families of glycosyl hydrolases.

Figure 2.
Figure 2. Overall view of the (α/α)[6] barrel of endoglucanase CelA. (a) Side view of CelA showing the active-site cleft at the N-terminal end of the inner helices. The 12 α helices forming the barrel involve residues Gln52–Arg70, Ser94–Cys106, Gln110–Lys121, Thr151–Trp168, Tyr176–Cys191, Pro218–Thr228, Arg232–Val247, Tyr282–Phe293, Gln296–Ala310, Ala334–Ala343, Leu350–Ala362 and Tyr372–Ile384 (as defined by PROCHECK [35]). (b) Stereo Cα trace of CelA, viewed along the barrel axis. Amino acid positions are labeled every 20 residues. Figure 2. Overall view of the (α/α)[6] barrel of endoglucanase CelA. (a) Side view of CelA showing the active-site cleft at the N-terminal end of the inner helices. The 12 α helices forming the barrel involve residues Gln52–Arg70, Ser94–Cys106, Gln110–Lys121, Thr151–Trp168, Tyr176–Cys191, Pro218–Thr228, Arg232–Val247, Tyr282–Phe293, Gln296–Ala310, Ala334–Ala343, Leu350–Ala362 and Tyr372–Ile384 (as defined by PROCHECK [[4]35]). (b) Stereo Cα trace of CelA, viewed along the barrel axis. Amino acid positions are labeled every 20 residues.

Figure 4.
Figure 4. Protein–carbohydrate interactions in the CelA–cellobiose complex. (a) Stereoview showing stacking interactions between sugar rings and aromatic amino acid side chains. (b) Schematic diagram of atomic contacts. Hydrogen bonds are indicated with dashed lines, the corresponding distances are given in å. Several water molecules (labeled ‘O[w]’) mediate enzyme-substrate interactions. Figure 4. Protein–carbohydrate interactions in the CelA–cellobiose complex. (a) Stereoview showing stacking interactions between sugar rings and aromatic amino acid side chains. (b) Schematic diagram of atomic contacts. Hydrogen bonds are indicated with dashed lines, the corresponding distances are given in å. Several water molecules (labeled ‘O[w]’) mediate enzyme-substrate interactions.

The above figures are reprinted by permission from Cell Press: Structure (1996, 4, 265-275) copyright 1996.

Secondary reference #1

Title

Crystallization of a family 8 cellulase from clostridium thermocellum.

Authors

H.Souchon, P.Béguin, P.M.Alzari.

Ref.

Proteins, 1996, 25, 134-136.

PubMed id

8727326