Transient unfolding of trypsin-digested chromatin core particles

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Nucleosomes are the fundamental units of DNA packaging in eukaryotes.
• Histone N-terminal tails play crucial roles in chromatin structure and function.
• Understanding nucleosome stability is key to deciphering gene regulation.

Purpose of the Study:

• To investigate the impact of N-terminal histone sequence cleavage on nucleosome core particle structure and stability.
• To characterize the structural transitions induced by partial proteolysis of histones.

Main Methods:

• Limited digestion of nucleosome core particles using trypsin.
• Analysis of structural changes using sedimentation assays.
• Circular dichroism spectroscopy to monitor conformational changes.
• Nuclease-cutting assays to assess DNA accessibility.

Main Results:

• Trypsin digestion removed 10-30 amino acids from histone N-terminal sequences.
• Proteolyzed nucleosome core particles exhibited salt-dependent structural transitions.
• Intact nucleosome cores remained unaffected under the same experimental conditions.
• Transitions were attributed to transient unfolding of terminal segments due to increased net negative charge.

Conclusions:

• Cleavage of histone N-terminal domains partially destabilizes nucleosome core particles.
• The compact nucleosome structure is not irreversibly disrupted by N-terminal histone excision.
• These findings shed light on the role of histone tails in maintaining nucleosome integrity.