9M5D | pdb_00009m5d

Crystal structure of S. aureus protein A bound to a human single-domain antibody


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 3.57 Å
  • R-Value Free: 
    0.271 (Depositor), 0.277 (DCC) 
  • R-Value Work: 
    0.233 (Depositor), 0.237 (DCC) 
  • R-Value Observed: 
    0.235 (Depositor) 

Starting Model: experimental
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wwPDB Validation   3D Report Full Report


This is version 1.0 of the entry. See complete history


Literature

A synergistic generative-ranking framework for tailored design of therapeutic single-domain antibodies.

Kong, Y.Shi, J.Wu, F.Zhao, T.Wang, R.Zhu, X.Xu, Q.Song, Y.Li, Q.Wang, Y.Gao, X.Yang, Y.Feng, Y.Wang, Z.Ge, W.Wu, Y.Yang, Z.Yao, J.Ying, T.

(2025) Cell Discov 11: 85-85

  • DOI: https://doi.org/10.1038/s41421-025-00843-8
  • Primary Citation of Related Structures:  
    9M5D, 9M6J, 9M6O

  • PubMed Abstract: 

    Single-domain antibodies (sdAbs) have emerged as powerful therapeutic agents due to their small size, high stability, and superior tissue penetration. However, unlike conventional monoclonal antibodies (mAbs), sdAbs lack an Fc domain, limiting their functional versatility and manufacturability. To address this challenge, we developed TFDesign-sdAb, a deep learning-based generative-ranking framework that enables rational engineering of sdAbs with tailored functionalities. Our framework integrates a structure-aware diffusion model (IgGM) for large-scale candidate generation and a fine-tuned sorter (A2binder) that evaluates and prioritizes them based on predicted functionality. Unlike traditional CDR-focused approaches, TFDesign-sdAb optimizes both complementarity-determining regions (CDRs) and framework regions (FRs), allowing sdAbs to acquire new functional properties while maintaining antigen specificity. We validated our approach by conferring Protein A binding to human VHs and nanobodies that originally lacked this feature, achieving high expression rates, strong binding affinities, and successful purification via industry-standard Protein A affinity chromatography. High-resolution structural characterization (1.49 Å and 2.0 Å) of the redesigned sdAb-Protein A complexes revealed conserved FR-mediated binding motifs that recapitulate natural Fc-Protein A interactions, validating the accuracy of our model. Furthermore, our pipeline streamlined the antibody engineering process, achieving a 100% success rate in generating Protein A-binding sdAbs while maintaining their original antigen-binding affinity. This work demonstrates the power of AI-driven design in overcoming long-standing limitations in antibody engineering and presents a scalable, generalizable solution for enhancing sdAb functionality.


  • Organizational Affiliation
    • Key Laboratory of Medical Molecular Virology (MOE/NHC/CAMS), Shanghai Institute of Infectious Disease and Biosecurity, School of Basic Medical Sciences, Department of Pulmonary and Critical Care Medicine, Department of Liver Surgery and Transplantation, Zhongshan Hospital, Fudan University, Shanghai, China.

Macromolecules
Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
n501A [auth D],
B [auth A]
120Homo sapiensMutation(s): 0 
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
Sequence Annotations
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  • Reference Sequence
Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 2
MoleculeChains Sequence LengthOrganismDetailsImage
Immunoglobulin G-binding protein AC [auth H],
D [auth B]
61Staphylococcus aureus subsp. aureus NCTC 8325Mutation(s): 0 
Gene Names: spaSAOUHSC_00069
UniProt
Find proteins for P02976 (Staphylococcus aureus (strain NCTC 8325 / PS 47))
Explore P02976 
Go to UniProtKB:  P02976
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP02976
Sequence Annotations
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  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 3.57 Å
  • R-Value Free:  0.271 (Depositor), 0.277 (DCC) 
  • R-Value Work:  0.233 (Depositor), 0.237 (DCC) 
  • R-Value Observed: 0.235 (Depositor) 
Space Group: I 4 2 2
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 173.973α = 90
b = 173.973β = 90
c = 79.611γ = 90
Software Package:
Software NamePurpose
PHENIXphasing
PHENIXrefinement
DIALSdata scaling
DIALSdata reduction

Structure Validation

View Full Validation Report



Entry History & Funding Information

Deposition Data


Funding OrganizationLocationGrant Number
National Natural Science Foundation of China (NSFC)China82394450

Revision History  (Full details and data files)

  • Version 1.0: 2025-11-12
    Type: Initial release