Cytoplasmically Produced Homodimeric Single Domain Antibody (sdAb) C22A/C99V variant against Staphylococcal enterotoxin B (SEB)

Experimental Data Snapshot

  • Resolution: 2.00 Å
  • R-Value Free: 0.242 
  • R-Value Work: 0.199 
  • R-Value Observed: 0.201 

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Structural and mutational analysis of a monomeric and dimeric form of a single domain antibody with implications for protein misfolding.

George, J.Compton, J.R.Leary, D.H.Olson, M.A.Legler, P.M.

(2014) Proteins 82: 3101-3116

  • DOI: https://doi.org/10.1002/prot.24671
  • Primary Citation of Related Structures:  
    4TYU, 4U05, 4U7S, 4W68, 4W70, 4W81

  • PubMed Abstract: 

    Camelid single domain antibodies (sdAb) are known for their thermal stability and reversible refolding. We have characterized an unusually stable sdAb recognizing Staphylococcal enterotoxin B with one of the highest reported melting temperatures (T(m) = 85°C). Unexpectedly, ∼10-20% of the protein formed a dimer in solution. Three other cases where <20% of the sdAb dimerized have been reported; however, this is the first report of both the monomeric and dimeric X-ray crystal structures. Concentration of the monomer did not lead to the formation of new dimer suggesting a stable conformationally distinct species in a fraction of the cytoplasmically expressed protein. Comparison of periplasmic and cytoplasmic expression showed that the dimer was associated with cytoplasmic expression. The disulfide bond was partially reduced in the WT protein purified from the cytoplasm and the protein irreversibly unfolded. Periplasmic expression produced monomeric protein with a fully formed disulfide bond and mostly reversible refolding. Crystallization of a disulfide-bond free variant, C22A/C99V, purified from the periplasm yielded a structure of a monomeric form, while crystallization of C22A/C99V from the cytoplasm produced an asymmetric dimer. In the dimer, a significant conformational asymmetry was found in the loop residues of the edge β-strands (S50-Y60) containing the highly variable complementarity determining region, CDR2. Two dimeric assemblies were predicted from the crystal packing. Mutation of a residue at one of the interfaces, Y98A, disrupted the dimer in solution. The pleomorphic homodimer may yield insight into the stability of misfolded states and the importance of the conserved disulfide bond in preventing their formation.

  • Organizational Affiliation

    Bowie State University, Bowie, 14000 Jericho Park Road, Maryland, 20715-9465.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Single domain antibodyA [auth B],
B [auth A]
133Lama glamaMutation(s): 0 
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 1 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
Query on SO4

Download Ideal Coordinates CCD File 
O4 S
Experimental Data & Validation

Experimental Data

  • Resolution: 2.00 Å
  • R-Value Free: 0.242 
  • R-Value Work: 0.199 
  • R-Value Observed: 0.201 
  • Space Group: C 2 2 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 66.893α = 90
b = 72.044β = 90
c = 116.103γ = 90
Software Package:
Software NamePurpose

Structure Validation

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Entry History & Funding Information

Deposition Data

Funding OrganizationLocationGrant Number
Defense Threat Reduction Agency (DTRA)United StatesCBCAL12-LS6-2-0036

Revision History  (Full details and data files)

  • Version 1.0: 2014-11-05
    Type: Initial release
  • Version 1.1: 2020-01-01
    Changes: Author supporting evidence, Database references, Derived calculations, Other, Source and taxonomy
  • Version 1.2: 2023-09-27
    Changes: Data collection, Database references, Refinement description