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Related Experiment Video

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Iterative Optimization of DNA Duplexes for Crystallization of SeqA-DNA Complexes

Iterative Optimization of DNA Duplexes for Crystallization of SeqA-DNA Complexes

Published on: November 1, 2012

DNA intercalation without flipping in the specific ThaI-DNA complex.

Malgorzata Firczuk¹, Marek Wojciechowski, Honorata Czapinska

¹International Institute of Molecular and Cell Biology, Warsaw, Poland.

Nucleic Acids Research

|September 24, 2010

Summary

The restriction enzyme ThaI uses an unusual DNA intercalation mechanism, with Met47 residues inserting into the DNA. This structural insight reveals novel DNA recognition strategies for type II endonucleases.

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Area of Science:

Biochemistry
Structural Biology
Molecular Biology

Background:

The PD-(D/E)XK type II restriction endonuclease ThaI cleaves the CG/CG sequence, producing blunt ends.
Previous bioinformatic analyses suggested conserved PD and (D/E)XK motifs are crucial for ThaI activity.

Purpose of the Study:

To elucidate the structural basis of ThaI's DNA recognition and cleavage mechanism.
To characterize the active site residues and unusual DNA binding mode of ThaI.

Main Methods:

X-ray crystallography was used to determine the 1.3 Å resolution structure of ThaI.
The structure was solved in complex with substrate DNA and a sodium or calcium ion, mimicking the active magnesium ion.

Main Results:

The active site residues were identified as Glu54, Asp82, and Lys93, suggesting the PD and (D/E)XK motifs are not essential.
ThaI exhibits an unconventional DNA recognition mechanism where two Met47 residues intercalate into the CG steps from the minor groove.
The DNA undergoes significant structural changes, including increased step rise and unwinding, to accommodate the intercalating Met47 residues without nucleotide flipping.

Conclusions:

The PD-(D/E)XK sequence motifs are incidental for ThaI function, with active site residues identified as Glu54, Asp82, and Lys93.
ThaI employs a unique DNA intercalation strategy distinct from other known restriction enzymes, highlighting novel DNA-protein interactions.
The study provides a detailed structural understanding of ThaI's unusual DNA binding and cleavage mechanism, advancing knowledge of type II restriction endonucleases.