Crystal Structure of Homoserine O-acetyltransferase (metA) from Bacillus Cereus with Homoserine

Experimental Data Snapshot

  • Resolution: 2.00 Å
  • R-Value Free: 0.246 
  • R-Value Work: 0.199 
  • R-Value Observed: 0.201 

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This is version 2.0 of the entry. See complete history


A Single Amino Acid Change is Responsible for Evolution of Acyltransferase Specificity in Bacterial Methionine Biosynthesis.

Zubieta, C.Arkus, K.A.J.Cahoon, R.E.Jez, J.M.

(2008) J Biol Chem 283: 7561

  • DOI: https://doi.org/10.1074/jbc.M709283200
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    Bacteria and yeast rely on either homoserine transsuccinylase (HTS, metA) or homoserine transacetylase (HTA; met2) for the biosynthesis of methionine. Although HTS and HTA catalyze similar chemical reactions, these proteins are typically unrelated in both sequence and three-dimensional structure. Here we present the 2.0 A resolution x-ray crystal structure of the Bacillus cereus metA protein in complex with homoserine, which provides the first view of a ligand bound to either HTA or HTS. Surprisingly, functional analysis of the B. cereus metA protein shows that it does not use succinyl-CoA as a substrate. Instead, the protein catalyzes the transacetylation of homoserine using acetyl-CoA. Therefore, the B. cereus metA protein functions as an HTA despite greater than 50% sequence identity with bona fide HTS proteins. This result emphasizes the need for functional confirmation of annotations of enzyme function based on either sequence or structural comparisons. Kinetic analysis of site-directed mutants reveals that the B. cereus metA protein and the E. coli HTS share a common catalytic mechanism. Structural and functional examination of the B. cereus metA protein reveals that a single amino acid in the active site determines acetyl-CoA (Glu-111) versus succinyl-CoA (Gly-111) specificity in the metA-like of acyltransferases. Switching of this residue provides a mechanism for evolving substrate specificity in bacterial methionine biosynthesis. Within this enzyme family, HTS and HTA activity likely arises from divergent evolution in a common structural scaffold with conserved catalytic machinery and homoserine binding sites.

  • Organizational Affiliation

    Donald Danforth Plant Science Center, St. Louis, Missouri 63132, USA.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
HOMOSERINE O-SUCCINYLTRANSFERASE301Bacillus cereusMutation(s): 0 
EC: (PDB Primary Data), (UniProt)
Find proteins for Q72X44 (Bacillus cereus (strain ATCC 10987 / NRS 248))
Explore Q72X44 
Go to UniProtKB:  Q72X44
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupQ72X44
Sequence Annotations
  • Reference Sequence
Small Molecules
Experimental Data & Validation

Experimental Data

  • Resolution: 2.00 Å
  • R-Value Free: 0.246 
  • R-Value Work: 0.199 
  • R-Value Observed: 0.201 
  • Space Group: P 41 2 2
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 96.39α = 90
b = 96.39β = 90
c = 75.58γ = 90
Software Package:
Software NamePurpose
XDSdata reduction
XSCALEdata scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2008-01-22
    Type: Initial release
  • Version 1.1: 2011-07-13
    Changes: Advisory, Version format compliance
  • Version 1.2: 2017-08-23
    Changes: Data collection
  • Version 1.3: 2019-04-10
    Changes: Data collection, Source and taxonomy
  • Version 2.0: 2023-11-15
    Changes: Atomic model, Data collection, Database references, Other