PDBsum entry 1x2a

Transferase

PDB id: 1x2a

Contents

Protein chains

396 a.a. *

Ligands

PDG ×2

Waters ×204

* Residue conservation analysis

PDB id:

1x2a

Name:

Transferase

Title:

Crystal structure of e.Coli aspat complexed with n-phosphopyridoxyl-d- glutamic acid

Structure:

Aspartate aminotransferase. Chain: a, b. Synonym: transaminase a, aspat. Engineered: yes

Source:

Escherichia coli. Organism_taxid: 562. Expressed in: escherichia coli. Expression_system_taxid: 562.

Biol. unit:

Dimer (from PQS)

Resolution:

2.20Å R-factor: 0.193 R-free: 0.234

Authors:

M.Goto

Key ref:

M.M.Islam et al. (2005). Binding of C5-dicarboxylic substrate to aspartate aminotransferase: implications for the conformational change at the transaldimination step. Biochemistry, 44, 8218-8229. PubMed id: 15938611 DOI: 10.1021/bi050071g

Date:

21-Apr-05 Release date: 14-Jun-05

Protein chains

P00509  (AAT_ECOLI) -  Aspartate aminotransferase from Escherichia coli (strain K12)

Seq: 396 a.a.

Struc: 396 a.a.

Enzyme reactions

• Enzyme class: E.C.2.6.1.1 - aspartate transaminase.
• Reaction: L-aspartate + 2-oxoglutarate = oxaloacetate + L-glutamate
• Cofactor: Pyridoxal 5'-phosphate

Pyridoxal 5'-phosphate (Bound ligand (Het Group name = PDG) matches with 57.69% similarity)

Molecule diagrams generated from .mol files obtained from the KEGG ftp site

reference

DOI no: 10.1021/bi050071g

Biochemistry 44:8218-8229 (2005)

PubMed id: 15938611

Binding of C5-dicarboxylic substrate to aspartate aminotransferase: implications for the conformational change at the transaldimination step.

M.M.Islam, M.Goto, I.Miyahara, H.Ikushiro, K.Hirotsu, H.Hayashi.

ABSTRACT

The mechanism for the reaction of aspartate aminotransferase with the C4 substrate, l-aspartate, has been well established. The binding of the C4 substrate induces conformational change in the enzyme from the open to the closed form, and the entire reaction proceeds in the closed form of the enzyme. On the contrary, little is known about the reaction with the C5 substrate, l-glutamate. In this study, we analyzed the pH-dependent binding of 2-methyl-l-glutamate to the enzyme and showed that the interaction between the amino group of 2-methyl-l-glutamate and the pyridoxal 5'-phosphate aldimine is weak compared to that between 2-methyl-l-aspartate and the aldimine. The structures of the Michaelis complexes of the enzyme with l-aspartate and l-glutamate were modeled on the basis of the maleate and glutarate complex structures of the enzyme. The result showed that l-glutamate binds to the open form of the enzyme in an extended conformation, and its alpha-amino group points in the opposite direction of the aldimine, while that of l-aspartate is close to the aldimine. These models explain the observations for 2-methyl-l-glutamate and 2-methyl-l-aspartate. The crystal structures of the complexes of aspartate aminotransferase with phosphopyridoxyl derivatives of l-glutamate, d-glutamate, and 2-methyl-l-glutamate were solved as the models for the external aldimine and ketimine complexes of l-glutamate. All the structures were in the closed form, and the two carboxylate groups and the arginine residues binding them are superimposable on the external aldimine complex with 2-methyl-l-aspartate. Taking these facts altogether, it was strongly suggested that the binding of l-glutamate to aspartate aminotransferase to form the Michaelis complex does not induce a conformational change in the enzyme, and that the conformational change to the closed form occurs during the transaldimination step. The hydrophobic residues of the entrance of the active site, including Tyr70, are considered to be important for promoting the transaldimination process and hence the recognition of the C5 substrate.