Structure, Assembly, and Mechanism of a PLP-Dependent Dodecameric l-Aspartate β-Decarboxylase
Resource
Structure 17 (4): 517-529
Journal
Structure
Journal Volume
17
Journal Issue
4
Pages
517-529
Start Page
517
End Page
529
ISSN
09692126
Date Issued
2009-04-15
Date
2009
Author(s)
Abstract
The type-I PLP enzyme l-aspartate β-decarboxylase converts aspartate to alanine and CO2. Similar to the homodimeric aminotransferases, its protein subunit comprises a large and a small domain, of 410 and 120 residues, respectively. The crystal structure reveals a dodecamer made of six identical dimers arranged in a truncated tetrahedron whose assembly involves tetramer and hexamer as intermediates. The additional helical motifs I and II participate in the oligomer formation. Triple mutations of S67R/Y68R/M69R or S67E/Y68E/M69E in motif I produced an inactive dimer. The PLP is bound covalently to Lys315 in the active site, while its phosphate group interacts with a neighboring Tyr134. Removal of the bulky side chain of Arg37, which overhangs the PLP group, improved the substrate affinity. Mutations in flexible regions produced the more active K17A and the completely inactive R487A. The structure also suggests that substrate binding triggers conformational changes essential for catalyzing the reaction.
Subjects
PROTEINS
SDGs
Type
journal article
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