28LK | pdb_000028lk

Crystal structure of complement-inhibiting protein ChiB of Borrelia recurrentis

• PDB DOI: https://doi.org/10.2210/pdb28LK/pdb

• Classification: PROTEIN BINDING
• Organism(s): Borrelia recurrentis
• Expression System: Escherichia coli
• Mutation(s): No 


• Deposited: 2026-02-05 Released: 2026-05-06 
• Deposition Author(s): Fritz-Wolf, K., Rahlfs, S., Przyborski, J.M., Stumpf, M., Roettgerding, F., Kraiczy, P.
• Funding Organization(s): LOEWE Center DRUID

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Experimental Data Snapshot

• Method: X-RAY DIFFRACTION
• Resolution: 1.50 Å
• R-Value Free: 
  0.215 (Depositor), 0.216 (DCC) 
• R-Value Work: 
  0.181 (Depositor), 0.181 (DCC) 
• R-Value Observed: 
  0.184 (Depositor) 

Literature

Complement inhibition by a unique cluster of immunomodulatory outer surface proteins of Borrelia recurrentis.

Rottgerding, F., Reyer, F., Gerlach, E., Amborn, M., Duschek, N., Schultze, T.G., Fingerle, V., Roome, C.M., Stumpf, M., Becker, K., Rahlfs, S., Przyborski, J.M., Kraiczy, P., Fritz-Wolf, K.

(2026) Nat Commun 17

• PubMed: 42050325 
• DOI: https://doi.org/10.1038/s41467-026-72359-y
• Primary Citation Related Structures: 
  28LI, 28LK


• PubMed Abstract: 
  

  Borrelia recurrentis, the agent of louse-borne relapsing fever, causes a poverty-associated, infectious disease of high mortality. Here, we identified and characterized five Complement targeting and Host Interacting proteins, ChiA to ChiE displaying immunomodulatory functions. Almost all Chi homologs inhibit complement activation by direct binding of key components, block membrane attack complex formation, and interact with plasminogen. Borrelia proteins protect susceptible spirochetes from complement-mediated killing and ChiB, ChiC, and ChiD facilitate serum resistance. X-ray structures of ChiA and ChiB, along with AlphaFold models of ChiC, ChiD, and ChiE, reveal a conserved, compact eight-helix fold with a central hydrophobic pocket and a unique S-domain-feature distinct from all known Borrelia proteins. Notably, ChiC and ChiE harbor conserved cysteines forming a reversible disulfide bridge, indicating redox-responsive function. Our findings identify a protein family of functionally related immune evasion factors, advancing our understanding of the underlying mechanisms of complement resistance in this neglected, human pathogenic microorganism.

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Organizational Affiliation: 
• Goethe University Frankfurt, University Hospital, Institute for Medical Microbiology and Infection Control, Frankfurt, Germany.
National Reference Center for Borrelia, Bavarian Health and Food Safety Authority, Oberschleissheim, Germany.
Max-Planck-Institute for Medical Research, Heidelberg, Germany.
Biochemistry and Molecular Biology, Interdisciplinary Research Centre, Justus Liebig University Giessen, Giessen, Germany.
Goethe University Frankfurt, University Hospital, Institute for Medical Microbiology and Infection Control, Frankfurt, Germany. [e-mail].
Max-Planck-Institute for Medical Research, Heidelberg, Germany. [e-mail].
Biochemistry and Molecular Biology, Interdisciplinary Research Centre, Justus Liebig University Giessen, Giessen, Germany. [e-mail].

Biological Assembly 1  

Global Symmetry: Asymmetric - C1 
Global Stoichiometry: Monomer - A1 

Biological assembly 1 assigned by authors.

Macromolecule Content 

• Total Structure Weight: 32.55 kDa 
• Atom Count: 2,373 
• Modeled Residue Count: 256 
• Deposited Residue Count: 283 
• Unique protein chains: 1

Macromolecules

Entity ID: 1
Molecule	Chains	Sequence Length	Organism	Details	Image
complement-inhibiting protein ChiB	A	283	Borrelia recurrentis	Mutation(s): 0  Gene Names: BDU_1020
UniProt
Find proteins for B5RN85 (Borrelia duttonii (strain Ly)) Explore B5RN85  Go to UniProtKB:  B5RN85

Small Molecules

Ligands 2 Unique
ID	Chains	Name / Formula / InChI Key	2D Diagram
LPP (Subject of Investigation/LOI)	B [auth A]	2-(HEXADECANOYLOXY)-1-[(PHOSPHONOOXY)METHYL]ETHYL HEXADECANOATE C35 H69 O8 P PORPENFLTBBHSG-MGBGTMOVSA-N
GOL	C [auth A], D [auth A], E [auth A]	GLYCEROL C3 H8 O3 PEDCQBHIVMGVHV-UHFFFAOYSA-N

Experimental Data & Validation

Experimental Data

• Method: X-RAY DIFFRACTION
• Resolution: 1.50 Å
• R-Value Free:  0.215 (Depositor), 0.216 (DCC) 
• R-Value Work:  0.181 (Depositor), 0.181 (DCC) 
• R-Value Observed: 0.184 (Depositor) 

Space Group: P 4₂ 2₁ 2

Unit Cell:

Length ( Å )	Angle ( ˚ )
a = 82.01	α = 90
b = 82.01	β = 90
c = 90.42	γ = 90

Software Package:

Software Name	Purpose
PHENIX	refinement
PHENIX	refinement
XDS	data reduction
XSCALE	data scaling
PHENIX	phasing

Structure Validation

Entry History 

& Funding Information

Deposition Data

• Released Date: 2026-05-06 
Deposition Author(s): Fritz-Wolf, K., Rahlfs, S., Przyborski, J.M., Stumpf, M., Roettgerding, F., Kraiczy, P.

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Funding Organization	Location	Grant Number
LOEWE Center DRUID	Germany	C3/E3

Revision History  

• Version 1.0: 2026-05-06
  Type: Initial release