Posttranslational modifications in human plasma MBL and human recombinant MBL

Area of Science:

• Biochemistry
• Immunology
• Proteomics

Background:

• Mannan-binding lectin (MBL) is a crucial serum protein in the innate immune system.
• MBL exists in various oligomeric forms and displays polypeptide heterogeneity due to post-translational modifications.
• These modifications are essential for stabilizing MBL's active conformation.

Purpose of the Study:

• To characterize the positions and frequencies of hydroxylation and glycosylation in MBL.
• To identify and characterize novel post-translational modifications in MBL.
• To investigate the impact of these modifications on MBL structure and function.

Main Methods:

• Mass spectrometry was employed on both reduced and enzyme-cleaved MBL (recombinant and plasma-derived).
• Analysis focused on identifying and quantifying post-translational modifications.
• Specific techniques were used to detect dehydroalanine formation via mass loss.

Main Results:

• The study reports, for the first time, the detailed patterns of hydroxylation and glycosylation in MBL.
• Variations in hydroxylation and glycosylation degrees are identified as inherent characteristics of collectins.
• A novel post-translational modification, dehydroalanine at Cys(216) (and occasionally Cys(202)), was detected in trace amounts, impairing disulfide bond formation.

Conclusions:

• Post-translational modifications, including hydroxylation, glycosylation, and the newly identified dehydroalanine, significantly contribute to MBL heterogeneity.
• These modifications are critical for maintaining MBL's structural integrity and functional activity.
• The findings provide new insights into the complex post-translational landscape of MBL and its role in immunity.