Crystal structure of the ADP-Mg-bound E. Coli MALK (Crystallized with ATP-Mg)

Experimental Data Snapshot

  • Resolution: 2.30 Å
  • R-Value Free: 0.271 
  • R-Value Work: 0.230 
  • R-Value Observed: 0.230 

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ATP hydrolysis is required to reset the ATP-binding cassette dimer into the resting-state conformation.

Lu, G.Westbrooks, J.M.Davidson, A.L.Chen, J.

(2005) Proc Natl Acad Sci U S A 102: 17969-17974

  • DOI: https://doi.org/10.1073/pnas.0506039102
  • Primary Citation of Related Structures:  
    2AWN, 2AWO

  • PubMed Abstract: 

    ATP-binding cassette (ABC) transporters couple ATP binding and hydrolysis to the movement of substances across the membrane; conformational changes clearly play an important role in the transporter mechanism. Previously, we have shown that a dimer of MalK, the ATPase subunit of the maltose transporter from Escherichia coli, undergoes a tweezers-like motion in a transport cycle. The MalK monomer consists of an N-terminal nucleotide binding domain and a C-terminal regulatory domain. The two nucleotide-binding domains in a dimer are either open or closed, depending on whether ATP is present, while the regulatory domains maintain contacts to hold the dimer together. In this work, the structure of MalK in a posthydrolysis state is presented, obtained by cocrystallizing MalK with ATP-Mg(2+). ATP was hydrolyzed in the crystallization drop, and ADP-Mg(2+) was found in the resulting crystal structure. In contrast to the ATP-bound form where two ATP molecules are buried in a closed interface between the nucleotide-binding domains, the two nucleotide-binding domains of the ADP-bound form are open, indicating that ADP, unlike ATP, cannot stabilize the closed form. This conclusion is further supported by oligomerization studies of MalK in solution. At low protein concentrations, ATP promotes dimerization of MalK, whereas ADP does not. The structures of dimeric MalK in the nucleotide-free, ATP-bound, and ADP-bound forms provide a framework for understanding the nature of the conformational changes that occur in an ATP-binding cassette transporter hydrolysis cycle, as well as how conformational changes in MalK are coupled to solute transport.

  • Organizational Affiliation

    Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Maltose/maltodextrin import ATP-binding protein malK
A, B, C, D
381Escherichia coli K-12Mutation(s): 0 
Gene Names: malK
Find proteins for P68187 (Escherichia coli (strain K12))
Explore P68187 
Go to UniProtKB:  P68187
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP68187
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 2.30 Å
  • R-Value Free: 0.271 
  • R-Value Work: 0.230 
  • R-Value Observed: 0.230 
  • Space Group: P 1 21 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 70.307α = 90
b = 102.667β = 90.81
c = 130.776γ = 90
Software Package:
Software NamePurpose
HKL-2000data reduction
SCALEPACKdata scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2005-12-13
    Type: Initial release
  • Version 1.1: 2008-05-01
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Source and taxonomy, Version format compliance
  • Version 1.3: 2023-08-23
    Changes: Data collection, Database references, Derived calculations, Refinement description