Amino acid sequence analysis of the glycopeptides from human complement component C3

Area of Science:

• Biochemistry
• Immunology
• Glycobiology

Background:

• Human complement component C3 is a critical protein in the innate immune system.
• Understanding its glycosylation is essential for elucidating its function and potential therapeutic applications.

Purpose of the Study:

• To precisely identify the sites of N-linked glycosylation on human complement component C3.
• To investigate the factors influencing glycosylation patterns at different sites.

Main Methods:

• Cleavage of C3 using trypsin in the presence of 2-propanol.
• Fractionation of the hydrolysate using reversed-phase high-performance liquid chromatography (HPLC).
• Unambiguous peptide sequencing to determine carbohydrate attachment sites.

Main Results:

• Two specific sites of glucosamine attachment were identified: Asn-63 on the beta-chain and Asn-268 on the alpha-chain.
• A potential glycosylation site at Asn-946 on the alpha-chain was found to be unmodified.
• Glycosylation status could not be explained by site accessibility or secondary structure, as all three sites are predicted reverse turns.

Conclusions:

• The study precisely maps the glycosylation sites on human complement component C3.
• Factors beyond simple accessibility or secondary structure influence C3 glycosylation.
• These findings contribute to a deeper understanding of C3 structure-function relationships in immunity.