PDBsum entry 2sli

Hydrolase

PDB id: 2sli

Contents

Protein chain

679 a.a. *

Ligands

SKD

Waters ×593

* Residue conservation analysis

PDB id:

2sli

Name:

Hydrolase

Title:

Leech intramolecular trans-sialidase complexed with 2,7-anhydro- neu5ac, the reaction product

Structure:

Intramolecular trans-sialidase. Chain: a. Fragment: devoid of n-terminal 28 residues. Engineered: yes

Source:

Macrobdella decora. North american leech. Organism_taxid: 6405. Gene: t7. Expressed in: escherichia coli bl21(de3). Expression_system_taxid: 469008. Expression_system_variant: de3.

Resolution:

1.80Å R-factor: 0.185 R-free: 0.224

Authors:

Y.Luo,S.C.Li,Y.T.Li,M.Luo

Key ref:

Y.Luo et al. (1999). The 1.8 A structures of leech intramolecular trans-sialidase complexes: evidence of its enzymatic mechanism. J Mol Biol, 285, 323-332. PubMed id: 9878409 DOI: 10.1006/jmbi.1998.2345

Date:

03-Oct-98 Release date: 27-Apr-99

Protein chain

Q27701  (NANL_MACDE) -  Anhydrosialidase from Macrobdella decora

Seq: 762 a.a.

Struc: 679 a.a.

Enzyme reactions

• Enzyme class: E.C.4.2.2.15 - anhydrosialidase.
• Pathway: Anhydrosialidase

DOI no: 10.1006/jmbi.1998.2345

J Mol Biol 285:323-332 (1999)

PubMed id: 9878409

The 1.8 A structures of leech intramolecular trans-sialidase complexes: evidence of its enzymatic mechanism.

Y.Luo, S.C.Li, Y.T.Li, M.Luo.

ABSTRACT

Intramolecular trans-sialidase from leech (Macrobdella decora) is the first member of the sialidase superfamily found to exhibit strict specificity towards the cleavage of terminal Neu5Acalpha2-->3Gal linkage in sialoglycoconjugates. Its release of 2,7-anhydro-Neu5Ac instead of Neu5Ac indicates that it catalyzes an intramolecular trans-sialosyl reaction. Crystal structures of its complexes with an inactive substrate analogue 2-propenyl-Neu5Ac, and with the product 2,7-anhydro-Neu5Ac, have been determined to 1.8 A resolution. The boat conformation of the pyranose observed in the complexes supports the proposed enzymatic mechanism that O7 of an axial 6-glycerol group attacks the positively charged C2 of the intermediate. A generalized mechanism is proposed for the sialidase superfamily.

Selected figure(s)

Figure 4.
Figure 4. F[o] - F[c] maps contoured at 2.0 s for the leech IT-sialidase complexes with (a) inactive substrate analogue 2-propenyl-Neu5Ac (the terminal carbon in the 2-propenyl is not shown). There is no density for the two terminal carbon groups in 2-propenyl. In addition, 6-glycerol appears disordered with a bulk density. (b) Product 2,7-anhydro-Neu5Ac; (c) also product 2,7-anhydro-Neu5Ac, soaked with substrate 3'-sialyllactose.

Figure 6.
Figure 6. Alternate enzymatic pathways by hydrolytic sialidases/neuraminidases, trans-sialidases, and IT-sialidases. The favored substrate conformation (left) in the active site is always a boat conformation. The differences between each enzymatic mechanism are the nucleophilic attacking atoms. These are activated water molecule in sialidase, the 3-hydroxyl of the galactose intrans-sialidase, and the 7-hydroxyl of the substrate sialic acid in IT-sialidase. The proximity of the hydroxyl groups is enforced by the conformation restraints imposed by the active site.

The above figures are reprinted by permission from Elsevier: J Mol Biol (1999, 285, 323-332) copyright 1999.

Figures were selected by an automated process.