Complete amino acid sequence of the catalytic chain of human complement subcomponent C1-r

Area of Science:

• Biochemistry
• Molecular Biology
• Proteomics

Background:

• The complement system plays a crucial role in innate and adaptive immunity.
• Complement factor C1r is a serine protease essential for the activation of the classical complement pathway.
• Understanding the primary structure of C1r is vital for elucidating its function and regulation.

Purpose of the Study:

• To determine the complete amino acid sequence of the human C1-r beta chain.
• To identify key functional residues, including the active site and disulfide bond locations.
• To investigate glycosylation patterns within the C1-r beta chain.

Main Methods:

• Sequence analysis of protein fragments generated by various proteolytic cleavages (CNBr, dilute acid hydrolysis, tryptic, staphylococcal protease).
• Identification of active site residues by homology to known serine proteases.
• Analysis of half-cystine residues to map disulfide bonds.
• Determination of glycosylation sites through asparagine residue identification.

Main Results:

• The human C1-r beta chain consists of 242 amino acids with a molecular weight of 27,096 Da.
• Strong homology was observed with other mammalian serine proteases.
• The catalytic triad residues (His-39, Asp-94, Ser-191) and conserved disulfide bonds were identified.
• Five half-cystine residues were found, with one likely involved in inter-chain disulfide bonding.
• Two N-linked glycosylation sites were located at Asn-51 and Asn-118.

Conclusions:

• The determined amino acid sequence provides a comprehensive structural basis for human C1-r beta chain function.
• The identified active site and disulfide bond patterns are conserved among serine proteases, with unique features in C1-r.
• The glycosylation sites may influence C1-r stability, interactions, or localization within the complement cascade.