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Updated: Jul 23, 2026
11:27
Studying DNA Looping by Single-Molecule FRET
Published on: June 28, 2014
Closed loops: persistence of the protein chain returns
Igor N Berezovsky1, Valery M Kirzhner, Alla Kirzhner
1Department of Structural Biology, The Weizmann Institute of Science, POB 26, Rehovot 76100, Israel. igor.berezovsky@weizmann.ac.il
Protein Engineering
|February 26, 2003
Summary
Globular proteins evolved from autonomous 30-residue loop-n-lock units. These ancient protein sequence prototypes are still detectable in modern proteins, primarily as conserved closed loops.
Area of Science:
- Protein structure and evolution
- Bioinformatics and computational biology
- Molecular biology
Background:
- Globular proteins are universally constructed from repeating loop-n-lock units of approximately 30 amino acids.
- A hypothesis suggests these units were initially autonomous during the early stages of protein evolution before forming longer chains.
Purpose of the Study:
- To investigate the presence and characteristics of hypothetical 30-residue sequence prototypes as remnants of early protein evolution.
- To analyze the evolutionary conservation patterns of these early protein elements in modern protein structures.
Main Methods:
- Extraction of sequence motifs from 23 complete bacterial proteomes.
- Identification of prototype-related sequence segments within the PDB_SELECT protein crystal structure database.
- Analysis of chain trajectories and sequence conservation in identified segments.
Main Results:
- A specific 32-residue prototype and related sequence segments were identified in protein structures.
- The majority of these segments correspond to closed loops, indicating structural conservation.
- Evolutionary diversification shows secondary structure loss precedes significant sequence divergence, with loop closure being the last conserved feature.
Conclusions:
- The study provides evidence for the existence of ancient protein sequence prototypes.
- Conserved closed loops are crucial for protein fold stability, explaining their evolutionary persistence.
- This supports the loop-n-lock unit hypothesis in protein structure and evolution.
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