MeaB, A Bacterial Homolog of MMAA, in its Apo form

Experimental Data Snapshot

  • Resolution: 2.20 Å
  • R-Value Free: 0.252 
  • R-Value Work: 0.197 
  • R-Value Observed: 0.199 

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Ligand Structure Quality Assessment 

This is version 1.3 of the entry. See complete history


A switch III motif relays signaling between a B12 enzyme and its G-protein chaperone.

Lofgren, M.Padovani, D.Koutmos, M.Banerjee, R.

(2013) Nat Chem Biol 9: 535-539

  • DOI: https://doi.org/10.1038/nchembio.1298
  • Primary Citation of Related Structures:  
    4JYB, 4JYC

  • PubMed Abstract: 

    Fidelity during cofactor assembly is essential for the proper functioning of metalloenzymes and is ensured by specific chaperones. MeaB, a G-protein chaperone for the coenzyme B12-dependent radical enzyme methylmalonyl-CoA mutase (MCM), uses the energy of GTP binding, hydrolysis or both to regulate cofactor loading into MCM, protect MCM from inactivation and rescue MCM that is inactivated during turnover. Typically, G proteins signal to client proteins using the conformationally mobile switch I and II loops. Crystallographic snapshots of MeaB reported herein reveal a new switch III element that has substantial conformational plasticity. Using alanine-scanning mutagenesis, we demonstrate that the switch III motif is critical for bidirectional signal transmission of the GTPase-activating protein activity of MCM and the chaperone functions of MeaB in the MeaB-MCM complex. Mutations in the switch III loop identified in patients corrupt this interprotein communication and lead to methylmalonic aciduria, an inborn error of metabolism.

  • Organizational Affiliation

    Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan, USA.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Methylmalonyl-CoA mutase accessory protein
A, B, C, D
337Methylorubrum extorquens AM1Mutation(s): 1 
Gene Names: meaBMexAM1_META1p0188
Find proteins for C5AP93 (Methylorubrum extorquens (strain ATCC 14718 / DSM 1338 / JCM 2805 / NCIMB 9133 / AM1))
Explore C5AP93 
Go to UniProtKB:  C5AP93
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupC5AP93
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 1 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
Query on GDP

Download Ideal Coordinates CCD File 
C10 H15 N5 O11 P2
Binding Affinity Annotations 
IDSourceBinding Affinity
GDP PDBBind:  4JYC Kd: 200 (nM) from 1 assay(s)
Experimental Data & Validation

Experimental Data

  • Resolution: 2.20 Å
  • R-Value Free: 0.252 
  • R-Value Work: 0.197 
  • R-Value Observed: 0.199 
  • Space Group: C 1 2 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 185.463α = 90
b = 58.377β = 110.07
c = 155.28γ = 90
Software Package:
Software NamePurpose
Blu-Icedata collection
XDSdata reduction
XSCALEdata scaling

Structure Validation

View Full Validation Report

Ligand Structure Quality Assessment 

Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2013-07-24
    Type: Initial release
  • Version 1.1: 2013-08-14
    Changes: Database references
  • Version 1.2: 2013-09-11
    Changes: Database references
  • Version 1.3: 2023-09-20
    Changes: Data collection, Database references, Derived calculations, Refinement description