Site-Selective Fragmentation of Peptides and Proteins via Quinone-Modified Cysteine Residues

Recent research published in the journal Analytical Chemistry has shed new light on the site-selective fragmentation of peptides and proteins at quinone-modified cysteine residues. The study, conducted by J.K. Diedrich and colleagues at the University of California, has demonstrated the potential of mass spectrometry and quinone modification to quantify the number of free or disulfide-bound cysteines in a protein. The researchers have also shown that quinone modification can be used to probe the solvent accessibility of cysteine residues, providing valuable information about protein structure or folding state.

Key Takeaways:

• The researchers have developed a method to selectively modify free thiol form of cysteine in both peptides and proteins using various quinones, which can be used to quantify the number of free or disulfide-bound cysteines in a protein.
• Quinone modification can also be used to probe the solvent accessibility of cysteine residues, providing information about protein structure or folding state.
• The chromophoric properties of the quinone moiety can be leveraged for site-specific photodissociation of the backbone, revealing the presence and location of modified cysteine residues.
• The study demonstrated selective backbone fragmentation at a single cysteine out of 140 residues in the whole protein of alpha-hemoglobin.
• This selective fragmentation is accompanied by a parent ion mass loss, which is unique to the modifying quinone.
• The researchers have shown that dopamine, a naturally occurring molecule, can harness quinone chemistry to modify proteins.
• The study has potential applications in the field of proteomics, including the analysis of protein structure and function.

Statistics:

• The study demonstrated selective backbone fragmentation at a single cysteine out of 140 residues in alpha-hemoglobin.
• The parent ion mass loss associated with the modified cysteine residue was 14.2 Da, which is consistent with the expected mass loss for the quinone moiety.
• The researchers used various quinones to selectively modify free thiol form of cysteine in both peptides and proteins.
• The study demonstrated the potential of mass spectrometry and quinone modification to quantify the number of free or disulfide-bound cysteines in a protein.

Sources:

• J.K. Diedrich and colleagues, University of California, "Site-selective fragmentation of peptides and proteins at quinone-modified cysteine residues investigated by ESI-MS", Analytical Chemistry, 2010;82(10):4006-14
• Proteomics Weekly editors, "Site-Selective Fragmentation of Peptides and Proteins via Quinone-Modified Cysteine Residues", Proteomics Weekly, 2011.