Serum amyloid P component in mink, a non-glycosylated protein with affinity for phosphorylethanolamine and phosphorylcholine.

Experimental AA amyloidosis in the mink is used as a model for the amyloid disease process. In that context it is important to characterize the different proteins involved in the amyloid formation. In the present work, we have characterized the serum amyloid P component (SAP) in mink. SAP was purified from serum by affinity chromatography using phosphorylethanolamine-coupled ECH-sepharose 4B. SDS-PAGE showed one major protein band (approximately 26 kDa) together with one minor band (10% of the major band) with a higher molecular mass (approximately 30 kDa) corresponding to a non-glycosylated and a glycosylated variant. All SAP molecules elucidated so far have at least one major subunit that is heavily glycosylated. It is therefore the first time that a non-glycosylated SAP protein is found in a mammalian species. The amino acid sequence was established using Edman degradation and mass spectrometry. As expected, the protein showed high homology with the other mammalian SAP molecules, ranging from 73% (human) to 63% (mouse). The SAP protein showed affinity for phosphorylcholine and thus expressed CRP-like properties.

The amino acid sequence of a glycosylated AL-chain from a patient with primary amyloidosis.

An amyloid fibril protein (Owe) related to primary amyloidosis was found to be a glycosylated complete immunoglobulin light chain (AL). The amino acid sequence revealed a protein composed of 214 residues and with a glycosylation site in position 20. The sequence established an AL V-region corresponding to a kappa 1b germline gene, but differs from that in 12 positions. Eight of them are in the FR-regions, positions 7, 13, 20, 42, 46, 60, 76 and 79. The J-segment is that of JkappaII.