The amino acid sequence and carbohydrate composition of an immunoglobulin kappa light chain amyloid fibril protein (AL) of variable subgroup I

Abstract

The amino acid sequence of a carbohydrate containing amyloid fibril protein LW of immunoglobulin-light chain type (AL) was determined. The protein was isolated from the spleen of a patient with myeloma-associated amyloidosis. The molecular mass of this protein was found to be in the range of 15–20 kDa including an oligosaccharide chain linked to it. AL protein LW consisted of different sized fragments of kappa chains (109–141 amino acids) degraded from the C-terminal end with a N-glycosylation site in position 74. The molecular mass of the carbohydrate core linked to Asn-74 was approximately 3 kDa. The amino acid sequence determination involved automatic Edman degradation directly on the protein, and of polypeptides obtained after cleaving the protein with CNBr, BNPS-skatole, trypsin, Staphylococcus aureus V8 protease (protease aureus), and cleavage of the protease aureus peptide PAD-3 with thermolysin. By sequence homology to other kappa-chains the AL protein LW was shown to be of the VkI subgroup. A protease aureus peptide and a thermolyticpeptide both containing the carbohydrate were isolated and characterized, and the location of an oligosaccharide chain linked to asparagine was established.

Key Words:

• carbohydrate
• immunoglobulin
• kappa subgroup i
• light chains