Expression of melanotransferrin isoforms in human serum: relevance to Alzheimer's disease.
Levels of soluble melanotransferrin in serum have been reported to be higher in patients with Alzheimer's disease than in control subjects. The present study investigated melanotransferrin in human body fluids in the light of these findings. To clarify the correlation between melanotransferrin and Alzheimer's disease, the melanotransferrin content was determined by non-reducing, denaturing SDS/PAGE and Western blotting. Under these conditions, serum melanotransferrin migrated at 79 and 82 kDa. Melanotransferrin antigenicity and the relative proportions of the two forms were very sensitive to factors that altered its conformation, including disulphide bridges, pH and bivalent cations. Serum melanotransferrin levels were not significantly different between control subjects and patients with Alzheimer's disease using whole serum, EDTA-supplemented serum or serum immunoglobulin-depleted by Protein G-Sepharose and enriched by affinity precipitation with the lectin from Asparagus pea. Glycosylated forms of serum melanotransferrin bound to Asparagus lectin manifested similar patterns on two-dimensional gel electrophoresis in samples from controls and Alzheimer's disease subjects. Melanotransferrin was also present in saliva and at a high level in urine, but contents were similar in controls and patients with Alzheimer's disease. Together, these results demonstrate that serum melanotransferrin exists in various conformations depending on the binding of bivalent cations or following post-translational modification. These data also indicate that human serum melanotransferrin levels are unchanged in subjects with Alzheimer's disease.
Desrosiers
Richard R
RR
Laboratoire de médecine moléculaire, Hôpital Sainte-Justine, Université du Québec à Montréal, C. P. 8888, Succursale Centre-ville, Montréal, Québec, Canada H3C 3P8.
Bertrand
Yanick
Y
Nguyen
Quynh-Tran
QT
Demeule
Michel
M
Gabathuler
Reinhard
R
Kennard
Malcolm L
ML
Gauthier
Serge
S
Béliveau
Richard
R
D000544:Alzheimer Disease / Q000097:blood* / Q000175:diagnosis; D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D000951:Antigens, Neoplasm; D002021:Buffers; D002413:Cations, Divalent / Q000737:chemistry; D002460:Cell Line; D011232:Chemical Precipitation; D006224:Cricetinae; D015180:Electrophoresis, Gel, Two-Dimensional; D006031:Glycosylation; D006801:Humans; D007136:Immunoglobulins / Q000378:metabolism; D037102:Lectins / Q000737:chemistry; D058950:Melanoma-Specific Antigens; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000097:blood* / Q000737:chemistry / Q000276:immunology / Q000652:urine; D009419:Nerve Tissue Proteins / Q000378:metabolism; D037121:Plant Lectins / Q000737:chemistry; D011487:Protein Conformation / Q000187:drug effects; D020033:Protein Isoforms / Q000096:biosynthesis / Q000097:blood / Q000737:chemistry / Q000276:immunology; D011499:Protein Processing, Post-Translational; D012471:Salivary Proteins and Peptides / Q000737:chemistry; D012680:Sensitivity and Specificity; D013205:Staphylococcal Protein A / Q000378:metabolism
D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; D002021:Buffers; D002413:Cations, Divalent; C029152:G-substrate; D007136:Immunoglobulins; D037102:Lectins; D058950:Melanoma-Specific Antigens; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D037121:Plant Lectins; D020033:Protein Isoforms; D012471:Salivary Proteins and Peptides; D013205:Staphylococcal Protein A