PDBsum entry: 1x1h

Lyase

PDB id: 1x1h

Contents

Protein chain

752 a.a. *

Waters ×407

* Residue conservation analysis

PDB id:

1x1h

Name:

Lyase

Title:

Crystal structure of xanthan lyase (n194a)

Structure:

Xanthan lyase. Chain: a. Fragment: residues 26-777. Engineered: yes. Mutation: yes

Source:

Bacillus sp. Gl1. Organism_taxid: 84635. Expressed in: escherichia coli. Expression_system_taxid: 562.

Resolution:

2.30Å R-factor: 0.185 R-free: 0.235

Authors:

Y.Maruyama,W.Hashimoto,B.Mikami,K.Murata

Key ref:

Y.Maruyama et al. (2005). Crystal structure of Bacillus sp. GL1 xanthan lyase complexed with a substrate: insights into the enzyme reaction mechanism. J Mol Biol, 350, 974-986. PubMed id: 15979090 DOI: 10.1016/j.jmb.2005.05.055

Date:

04-Apr-05 Release date: 19-Jul-05

Protein chain

Q9AQS0  (Q9AQS0_BACGL) -  Xanthan lyase

Seq: 930 a.a.

Struc: 752 a.a.*

* PDB and UniProt seqs differ at 1 residue position (black cross)

 Gene Ontology (GO) functional annotation 

• Cellular component: extracellular region (1 term)
• Biological process: carbohydrate metabolic process (1 term)
• Biochemical function: catalytic activity (4 terms)

DOI no: 10.1016/j.jmb.2005.05.055

J Mol Biol 350:974-986 (2005)

PubMed id: 15979090

Crystal structure of Bacillus sp. GL1 xanthan lyase complexed with a substrate: insights into the enzyme reaction mechanism.

Y.Maruyama, W.Hashimoto, B.Mikami, K.Murata.

ABSTRACT

Bacillus sp. GL1 xanthan lyase, a member of polysaccharide lyase family 8 (PL-8), acts exolytically on the side-chains of pentasaccharide-repeating polysaccharide xanthan and cleaves the glycosidic bond between glucuronic acid (GlcUA) and pyruvylated mannose (PyrMan) through a beta-elimination reaction. To clarify the enzyme reaction mechanism, i.e. its substrate recognition and catalytic reaction, we determined crystal structures of a mutant enzyme, N194A, in complexes with the product (PyrMan) and a substrate (pentasacharide) and in a ligand-free form at 1.8, 2.1, and 2.3A resolution. Based on the structures of the mutant in complexes with the product and substrate, we found that xanthan lyase recognized the PyrMan residue at subsite -1 and the GlcUA residue at +1 on the xanthan side-chain and underwent little interaction with the main chain of the polysaccharide. The structure of the mutant-substrate complex also showed that the hydroxyl group of Tyr255 was close to both the C-5 atom of the GlcUA residue and the oxygen atom of the glycosidic bond to be cleaved, suggesting that Tyr255 likely acts as a general base that extracts the proton from C-5 of the GlcUA residue and as a general acid that donates the proton to the glycosidic bond. A structural comparison of catalytic centers of PL-8 lyases indicated that the catalytic reaction mechanism is shared by all members of the family PL-8, while the substrate recognition mechanism differs.

Selected figure(s)

Figure 4.
Figure 4. Active center of xanthan lyase (stereo diagram). (a) Superpositioning of wild-type/PyrMan (grey), N194A/PyrMan (cyan), and N194A/pentasaccharide (yellow). Bound sugar residues and surrounding amino acid residues are shown as a stick model. Red indicates oxygen and blue nitrogen atoms of amino acid residues. (b) Structure and interaction of xanthan disaccharide (PyrMan-GlcUA) and neighboring amino acid residues in the N194A/pentasaccharide complex. Thin lines indicate hydrogen bond interactions.

Figure 6.
Figure 6. Proposed model of the xanthan lyase reaction mechanism. (a) The substrate is bound to the active site cleft of xanthan lyase and orientated in the proper conformation via interactions with amino acid residues including hydrogen bonds of Asn194 and His246 with the carboxyl group of GlcUA. The hydroxyl group of Tyr255 is located close to the oxygen atom of the glycosidic bond to be cleaved and the C-5 atom of GlcUA. (b) Tyr255 extracts the C-5 proton of the GlcUA residue and subsequently donates the proton to the oxygen atom of the glycosidic bond, cleaving the glycosidic bond and forming a double bond between the C-4 and C-5 atoms of GlcUA.

The above figures are reprinted by permission from Elsevier: J Mol Biol (2005, 350, 974-986) copyright 2005.

Figures were selected by an automated process.