Crystal structure of Ricin A-chain in complex with the cyclic tetranucleotide inhibitor, a transition state analogue

Experimental Data Snapshot

  • Resolution: 2.00 Å
  • R-Value Free: 0.254 
  • R-Value Work: 0.219 
  • R-Value Observed: 0.221 

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Transition state analogues in structures of ricin and saporin ribosome-inactivating proteins.

Ho, M.C.Sturm, M.B.Almo, S.C.Schramm, V.L.

(2009) Proc Natl Acad Sci U S A 106: 20276-20281

  • DOI: https://doi.org/10.1073/pnas.0911606106
  • Primary Citation of Related Structures:  
    3HIO, 3HIQ, 3HIS, 3HIT, 3HIV, 3HIW

  • PubMed Abstract: 

    Ricin A-chain (RTA) and saporin-L1 (SAP) catalyze adenosine depurination of 28S rRNA to inhibit protein synthesis and cause cell death. We present the crystal structures of RTA and SAP in complex with transition state analogue inhibitors. These tight-binding inhibitors mimic the sarcin-ricin recognition loop of 28S rRNA and the dissociative ribocation transition state established for RTA catalysis. RTA and SAP share unique purine-binding geometry with quadruple pi-stacking interactions between adjacent adenine and guanine bases and 2 conserved tyrosines. An arginine at one end of the pi-stack provides cationic polarization and enhanced leaving group ability to the susceptible adenine. Common features of these ribosome-inactivating proteins include adenine leaving group activation, a remarkable lack of ribocation stabilization, and conserved glutamates as general bases for activation of the H(2)O nucleophile. Catalytic forces originate primarily from leaving group activation evident in both RTA and SAP in complex with transition state analogues.

  • Organizational Affiliation

    Department of Biochemistry, Albert Einstein College of Medicine, Yeshiva University, Bronx, NY 10461, USA.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Ricin268Ricinus communisMutation(s): 0 
Find proteins for P02879 (Ricinus communis)
Explore P02879 
Go to UniProtKB:  P02879
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP02879
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 2 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
Query on C2X

Download Ideal Coordinates CCD File 
B [auth A]9,9'-{(2R,3R,3aR,5S,7aR,9R,10R,10aR,12S,23R,25aR,27R,28R,28aR,30S,32aR,35aR,37S,39aR)-9-(6-amino-9H-purin-9-yl)-34-[(4-amino-5H-pyrrolo[3,2-d]pyrimidin-7-yl)methyl]-5,12,23,30,37-pentahydroxy-3,10,28-trimethoxy-5,12,23,30,37-pentaoxidotetracosahydro-2H,7H,25H-trifuro[3,2-f:3',2'-l:3'',2''-x]pyrrolo[3,4-r][1,3,5,9,11,15,17,21,23,27,29,2,4,10,16,22,28]undecaoxazapentaphosphacyclopentatriacontine-2,27-diyl}bis(2-amino-3,9-dihydro-6H-purin-6-one)
C51 H72 N21 O29 P5
Query on SO4

Download Ideal Coordinates CCD File 
O4 S
Binding Affinity Annotations 
IDSourceBinding Affinity
C2X PDBBind:  3HIO Ki: 300 (nM) from 1 assay(s)
Experimental Data & Validation

Experimental Data

  • Resolution: 2.00 Å
  • R-Value Free: 0.254 
  • R-Value Work: 0.219 
  • R-Value Observed: 0.221 
  • Space Group: P 41 21 2
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 68.632α = 90
b = 68.632β = 90
c = 134.681γ = 90
Software Package:
Software NamePurpose
DENZOdata reduction
SCALEPACKdata scaling
PDB_EXTRACTdata extraction
CBASSdata collection
HKL-2000data reduction

Structure Validation

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Ligand Structure Quality Assessment 

Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2009-12-08
    Type: Initial release
  • Version 1.1: 2011-07-13
    Changes: Advisory, Version format compliance
  • Version 1.2: 2017-11-01
    Changes: Refinement description
  • Version 1.3: 2024-02-21
    Changes: Data collection, Database references, Derived calculations