Structural and evolutionary classification of Type II restriction enzymes based on theoretical and experimental...

Area of Science:

• Biochemistry
• Structural Biology
• Bioinformatics

Background:

• Type II restriction enzymes (REases) are functionally similar but sequence-diverse, historically classified as ORFans.
• Limited experimental structures exist for the vast number of known REase sequences.
• Existing structural classifications include PD-(D/E)XK, PLD, half-pipe, GIY-YIG, and HNH folds.

Purpose of the Study:

• To comprehensively classify all Type II REase sequences based on predicted and known three-dimensional folds.
• To evaluate existing structural assignments and predictions for Type II REases.
• To identify novel REase folds and potential targets for structural determination.

Main Methods:

• Analysis of all Type II REase sequences from REBASE and their homologs from NCBI databases.
• Domain architecture analysis and prediction of three-dimensional folds using bioinformatics.
• Comparison and critical evaluation of previously reported structural assignments.

Main Results:

• 199 (69%) of 289 characterized Type II REases contain the PD-(D/E)XK fold; 24 (8%) contain the HNH fold.
• Including putative REases, PD-(D/E)XK and HNH folds account for 48% and 30%, respectively.
• 56 characterized and 521 predicted REases remain unassigned, suggesting novel fold architectures.

Conclusions:

• The PD-(D/E)XK fold is the most prevalent among characterized Type II REases.
• A significant number of Type II REases, particularly those with unassigned folds, represent promising targets for structural genomics.
• This study provides a crucial sequence-structure relationship map for Type II REases, guiding future research.