Removal of N-terminal blocking groups from proteins

Area of Science:

• Biochemistry
• Proteomics
• Analytical Chemistry

Background:

• N-terminal protein sequencing is vital for protein identification and characterization.
• Many proteins possess N-terminal blocking groups that hinder direct sequencing.
• Existing methods for removing these blocks are often inefficient or incompatible with certain protein types.

Purpose of the Study:

• To present and detail two enzymatic methods for the removal of N-terminal blocking groups in proteins.
• To provide protocols for both pyroglutamate aminopeptidase and acylaminoacyl-peptide hydrolase applications.
• To describe complementary chemical methods for protein fragmentation and peptide modification.

Main Methods:

• Enzymatic unblocking using pyroglutamate aminopeptidase for N(alpha)-pyrrolidone carboxyl-proteins.
• Enzymatic unblocking using acylaminoacyl-peptide hydrolase for N(alpha)-acyl-proteins, following protein fragmentation.
• Chemical blocking of newly generated peptides with succinic anhydride or phenylisothiocyanate/performic acid.
• Colorimetric assay for pyroglutamate aminopeptidase activity.
• Acid-catalyzed hydrolysis, methanolysis, hydrazinolysis, and beta-elimination for N-terminal unblocking.
• Chemical removal of acetyl, alkanoyl, and formyl groups.

Main Results:

• Demonstrated the utility of pyroglutamate aminopeptidase for solution and membrane-bound proteins.
• Established a workflow for acylaminoacyl-peptide hydrolase application involving protein fragmentation and selective peptide unblocking.
• Provided detailed protocols for various chemical and enzymatic unblocking strategies.
• Introduced a colorimetric assay for enzyme activity assessment.

Conclusions:

• Enzymatic methods offer efficient and specific strategies for removing N-terminal protein blocks.
• These protocols enhance the scope and accuracy of N-terminal sequence analysis.
• The presented methods are valuable tools for researchers in proteomics and protein chemistry.