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Sequence and structural links between distant ADP-ribosyltransferase families
1Department of Molecular Biology, DNAX Research Institute, Palo Alto, California 94304-1104, USA.
Advances in Experimental Medicine and Biology
|January 1, 1997
Summary
Structural analysis reveals a conserved catalytic domain fold across bacterial toxins like Pseudomonas aeruginosa exotoxin A (ETA), cholera toxin (LT), and diphtheria toxin (DT). This conserved structure, despite sequence variability, aids in identifying new ADP-ribosyl-transferase (ADPRT) families.
Area of Science:
- Biochemistry
- Structural Biology
- Genomics
Background:
- The 1986 low-resolution structure of Pseudomonas aeruginosa exotoxin A (ETA) first revealed the three-dimensional fold of an ADP-ribosyl-transferase (ADPRT) catalytic domain.
- This conserved fold is now recognized in other bacterial toxins, including cholera toxin-related heat-labile enterotoxin (LT), diphtheria toxin (DT), and pertussis toxin (PT).
Purpose of the Study:
- To analyze the conserved structural scaffold of ADPRT catalytic domains across various bacterial toxins.
- To investigate sequence variability and identify invariant residues critical for catalysis and binding.
- To explore evolutionary relationships between prokaryotic and eukaryotic ADPRTs and search for novel families.
Main Methods:
- Comparative analysis of solved crystal structures (ETA, LT, DT, PT) to identify conserved protein folds.
- Cocrystallography of toxins with inhibitors (ApUp) and substrates/ligands (AMP, nicotinamide, NAD) to understand binding and catalysis.
- Sequence threading of eukaryotic ADPRTs into the conserved prokaryotic scaffold.
Main Results:
- A core alpha+beta element scaffold is conserved across diverse ADPRT toxins, with significant sequence plasticity.
- Only a single glutamic acid residue is invariant and critical for catalytic activity.
- Cocrystal structures reveal interchangeable residues involved in catalysis and binding, consistent with experimental data.
- Structural concordance confirms and extends sequence-based relationships among prokaryotic ADPRTs.
- Eukaryotic ADPRTs can be reliably threaded into this conserved core fold.
Conclusions:
- The conserved ADPRT catalytic domain fold provides a robust framework for understanding toxin function and evolution.
- The plasticity in sequence, alongside conserved structural elements, facilitates the identification of new ADPRT families in sequence databases.
- Structural insights guide ongoing research into ADPRT relationships and the discovery of novel enzyme families.