Histone H1 structure probed by Staphylococcus aureus V8-proteinase

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Histone H1 plays a crucial role in chromatin condensation and gene regulation.
• The globular (G) domain of histone H1 is known for its resistance to proteolytic digestion.
• Understanding histone H1 structure is key to deciphering its function in DNA packaging.

Purpose of the Study:

• To investigate the proteolytic cleavage sites of histone H1 using Staphylococcus aureus V8-proteinase.
• To determine the structural implications of V8-proteinase cleavage on the histone H1 G-domain.
• To assess the suitability of V8-proteinase as a tool for probing histone H1 structure.

Main Methods:

• Proteolytic digestion of calf thymus histone H1 with Staphylococcus aureus V8-proteinase.
• Edman degradation for N-terminal sequencing of the resulting peptide.
• Chymotryptic fingerprinting to confirm the integrity of the C-terminal region.
• Circular dichroism spectroscopy to assess the folding state of histone H1 fragments.

Main Results:

• A major limit peptide (P1) of approximately 170 residues was generated, identified as H1 (42-210).
• Cleavage occurred at Glu-41 within the typically resistant G-domain, an unusual finding.
• The V8-proteinase cleavage product H1 (42-210) exhibited significantly reduced folding (20%) compared to other fragments (95-99%).
• The integrity of the G-domain's folding depends critically on residues 33-41, including a Gly-Pro-Pro sequence and a predicted beta-turn.

Conclusions:

• The unusual cleavage site at Glu-41 highlights the sensitivity of the G-domain under specific conditions.
• The reduced folding of H1 (42-210) indicates the importance of the N-terminal portion of the G-domain for its structural stability.
• Staphylococcus aureus V8-proteinase serves as a valuable structural probe for investigating histone H1 G-domain conformation.