Efficient Isothiocyanate Modification of Peptides Facilitates Structural Analysis by Radical-Directed Dissociation

Area of Science:

• Mass Spectrometry
• Chemical Biology
• Analytical Chemistry

Background:

• Radical-directed dissociation (RDD) is crucial for peptide structural characterization.
• A radical precursor is typically required for RDD, necessitating a facile attachment method.

Purpose of the Study:

• To explore a single-step modification of peptides using a "click" reaction with iodophenyl isothiocyanate.
• To evaluate the effectiveness of this modification for radical precursor attachment and subsequent RDD analysis.

Main Methods:

• Peptide modification via "click" reaction with iodophenyl isothiocyanate.
• Photodissociation yield analysis at 266 and 213 nm for different iodo isomers.
• Collisional activation for fragmentation analysis and electronic structure calculations.

Main Results:

• High yields of stable iodophenylthiourea-modified peptides were achieved.
• The 4-iodo isomer consistently showed the highest photodissociation yields.
• Fragmentation patterns were similar across different iodinated compounds, with notable differences in fragment abundance.

Conclusions:

• Iodophenyl isothiocyanate labeling combined with RDD effectively differentiates isomeric amino acids in peptides.
• This method offers a simplified approach for isomer evaluation in complex biological samples.
• The 4-iodo isomer is particularly effective for RDD applications.