HMGB binding to DNA: single and double box motifs

Area of Science:

• Molecular Biology
• Biophysics

Background:

• High mobility group (HMG) proteins are nuclear proteins that influence DNA interactions.
• HMG B proteins, with their HMG box domains, bind DNA's minor groove without sequence specificity, inducing DNA bending.

Purpose of the Study:

• To investigate the effects of single (HMGB2 box A) and double (HMGB1 box A+B) HMG box domains on double-stranded DNA (dsDNA) flexibility and stability.
• To compare the efficacy of single versus double HMG box domains in altering DNA properties.

Main Methods:

• Utilized a dual-beam optical tweezers system to extend dsDNA.
• Measured changes in DNA persistence length and bending angles in the presence of HMGB2(box A) and HMGB1(box A+B).

Main Results:

• Both single and double HMG box proteins reduced dsDNA persistence length, indicating increased flexibility.
• Single HMGB2(box A) induced an average DNA bend of 99+/-9 degrees.
• Double HMGB1(box A+B) induced an average DNA bend of 77+/-7 degrees.
• Both proteins stabilized dsDNA against denaturation, with the double box protein being effective at significantly lower concentrations.

Conclusions:

• HMG box proteins enhance DNA flexibility and stability.
• The double HMG box protein is more efficient, requiring lower concentrations to achieve similar effects compared to the single HMG box protein.
• Concentration-dependent effects suggest distinct binding mechanisms, including cooperative binding at higher concentrations for stabilization.