Crystal structure of lambda-Cro bound to a consensus operator at 3.0 A resolution

Area of Science:

• Structural Biology
• Molecular Biology
• Biochemistry

Background:

• Bacteriophage lambda Cro protein regulates gene expression.
• Understanding Cro-DNA interactions is crucial for molecular biology.
• Previous studies indicated significant conformational changes upon binding.

Purpose of the Study:

• To determine the high-resolution crystal structure of the Cro protein-DNA complex.
• To elucidate the detailed molecular interactions between Cro and its operator DNA.
• To understand the mechanism of DNA operator recognition and discrimination.

Main Methods:

• X-ray crystallography at 3.0 A resolution.
• Analysis of protein-DNA complex structure.
• Comparison with free protein structure and biochemical data.

Main Results:

• Detailed interactions between Cro side-chains and operator base-pairs revealed.
• Significant conformational changes observed: 53-degree subunit rotation in Cro and 40-degree DNA bending.
• Operator recognition primarily via hydrogen bonding and van der Waals contacts in the major groove.
• Discrimination between similar operators (OR3 vs. OR1) involves a combination of direct and indirect effects, with one van der Waals contact being key.

Conclusions:

• The high-resolution structure confirms and details previous low-resolution findings.
• Cro-DNA binding involves substantial protein and DNA structural rearrangements.
• Operator recognition is mediated by direct molecular contacts, with specific van der Waals interactions playing a critical role in sequence discrimination.