Which amino acids contribute to the positive charge of histones?

Histones are proteins that play a crucial role in packaging DNA in the cell nucleus, and they are known for their positively charged regions. The positive charge of histones is primarily due to the presence of specific amino acids that have basic side chains, which can accept protons and carry a positive charge at physiological pH.

Arginine and lysine are the amino acids that contribute significantly to the positive charge of histones. Arginine has a guanidinium group in its side chain, allowing it to have a strong positive charge, while lysine contains an amino group that can also be protonated, resulting in a positive charge. Their basic nature helps histones to bind tightly to the negatively charged DNA, facilitating the formation of nucleosomes and higher-order chromatin structures.

Other amino acids listed, such as serine, threonine, cysteine, methionine, glutamic acid, and aspartic acid, do not contribute to the positive charge in the same way. Instead, serine and threonine are polar but not charged at physiological pH, cysteine is primarily neutral but can form disulfide bonds, methionine is hydrophobic, and both glutamic acid and aspartic acid are negatively charged