Structure of siderophore binding protein BauB bound to a complex between two molecules of acinetobactin and ferric iron.

Experimental Data Snapshot

  • Resolution: 1.90 Å
  • R-Value Free: 0.214 
  • R-Value Work: 0.169 
  • R-Value Observed: 0.172 

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Crystal Structure of the Siderophore Binding Protein BauB Bound to an Unusual 2:1 Complex Between Acinetobactin and Ferric Iron.

Bailey, D.C.Bohac, T.J.Shapiro, J.A.Giblin, D.E.Wencewicz, T.A.Gulick, A.M.

(2018) Biochemistry 57: 6653-6661

  • DOI: https://doi.org/10.1021/acs.biochem.8b00986
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    The critical role that iron plays in many biochemical processes has led to an elaborate battle between bacterial pathogens and their hosts to acquire and withhold this critical nutrient. Exploitation of iron nutritional immunity is being increasingly appreciated as a potential antivirulence therapeutic strategy, especially against problematic multidrug resistant Gram-negative pathogens such as Acinetobacter baumannii. To facilitate iron uptake and promote growth, A. baumannii produces a nonribosomally synthesized peptide siderophore called acinetobactin. Acinetobactin is unusual in that it is first biosynthesized in an oxazoline form called preacinetobactin that spontaneously isomerizes to the final isoxazolidinone acinetobactin. Interestingly, both isomers can bind iron and both support growth of A. baumannii. To address how the two isomers chelate their ferric cargo and how the complexes are used by A. baumannii, structural studies were carried out with the ferric acinetobactin complex and its periplasmic siderophore binding protein BauB. Herein, we present the crystal structure of BauB bound to a bis-tridentate (Fe 3+ L 2 ) siderophore complex. Additionally, we present binding studies that show multiple variants of acinetobactin bind BauB with no apparent change in affinity. These results are consistent with the structural model that depicts few direct polar interactions between BauB and the acinetobactin backbone. This structural and functional characterization of acinetobactin and its requisite binding protein BauB provides insight that could be exploited to target this critical iron acquisition system and provide a novel approach to treat infections caused by this important multidrug resistant pathogen.

  • Organizational Affiliation

    Department of Chemistry , Washington University in St. Louis , One Brookings Drive , St. Louis , Missouri 63130 , United States.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
A, B
308Acinetobacter baumanniiMutation(s): 0 
Gene Names: bauB
Find proteins for Q76HK0 (Acinetobacter baumannii)
Explore Q76HK0 
Go to UniProtKB:  Q76HK0
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupQ76HK0
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 3 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
OPV (Subject of Investigation/LOI)
Query on OPV

Download Ideal Coordinates CCD File 
D [auth A],
E [auth A],
H [auth B],
I [auth B]
C16 H18 N4 O5
Query on EDO

Download Ideal Coordinates CCD File 
F [auth A],
J [auth B]
C2 H6 O2
Query on FE

Download Ideal Coordinates CCD File 
C [auth A],
G [auth B]
Binding Affinity Annotations 
IDSourceBinding Affinity
OPV Binding MOAD:  6MFL Kd: 160 (nM) from 1 assay(s)
Experimental Data & Validation

Experimental Data

  • Resolution: 1.90 Å
  • R-Value Free: 0.214 
  • R-Value Work: 0.169 
  • R-Value Observed: 0.172 
  • Space Group: P 1 21 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 37.762α = 90
b = 137.055β = 90.02
c = 56.208γ = 90
Software Package:
Software NamePurpose
MOSFLMdata reduction
Aimlessdata scaling

Structure Validation

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Entry History & Funding Information

Deposition Data

Funding OrganizationLocationGrant Number
National Institutes of Health/National Institute Of Allergy and Infectious Diseases (NIH/NIAID)United StatesAI116998

Revision History  (Full details and data files)

  • Version 1.0: 2018-11-21
    Type: Initial release
  • Version 1.1: 2019-05-01
    Changes: Data collection, Database references
  • Version 1.2: 2019-12-18
    Changes: Author supporting evidence
  • Version 1.3: 2023-10-11
    Changes: Data collection, Database references, Derived calculations, Refinement description