Trypsin digestion of core chromatin

Area of Science:

• Biochemistry
• Molecular Biology
• Chromatin Structure

Background:

• Core histones are fundamental components of chromatin, organizing DNA into nucleosomes.
• Understanding histone-DNA interactions is crucial for gene regulation and chromatin dynamics.

Purpose of the Study:

• To investigate the specific regions of core histones involved in DNA binding.
• To characterize the structural changes in histones and DNA upon enzymatic digestion.

Main Methods:

• Chicken erythrocyte core chromatin was subjected to extensive trypsin digestion (18 hours).
• Analysis of resulting peptides by molecular weight.
• Assessment of DNA supercoiling and histone secondary/tertiary structure using biophysical techniques.

Main Results:

• Trypsin digestion yielded five major limit peptides (8-10 kDa) from central histone regions, remaining bound to DNA.
• Basic amino- and carboxyl-terminal regions were degraded into small peptides, dissociating from DNA.
• DNA supercoiling decreased, and histone tertiary structure was perturbed, but secondary structure in DNA-bound fragments remained intact.
• Dissociation of degraded fragments from DNA led to a 50% loss of their secondary (alpha-helical) structure.

Conclusions:

• DNA exhibits strong binding to the central, alpha-helical segments of core histone polypeptides.
• The terminal regions of core histones are less critical for DNA binding and are susceptible to proteolysis.
• The interaction between DNA and histone alpha-helices is essential for maintaining chromatin structure and stability.