Heterogeneity of the human corticotropin-releasing factor-binding protein.
Human corticotropin-releasing factor (hCRF), secreted by the placenta, principally in the third trimester, is specifically bound in the peripheral circulation to a 37-kDa binding protein (CRF-BP). This complex is cleared from the circulation. We postulate that the protein may be returned to the blood in a form that is immunologically altered and not well recognized by the reported RIAs. We report that a stable isoform can result from temporary denaturation of recombinant CRF-BP by 8 mol/L urea. This isoform, urea-treated binding protein, which can bind CRF, has been found to bind to an antibody raised against a synthetic peptide comprising the first 24 amino acid residues of CRF-BP, but not to a second similar N-terminal antibody, although it was closely matched in titer. Urea-treated binding protein also cross-reacts poorly in the RIA with CRF-BP. It is proposed that as a result of in vivo post-ligand binding events, isoforms may be susceptible to cleavage. After affinity purification, which involves denaturation, recombinant CRF-BP was often found to be cleaved after storage in the presence of protease inhibitors. Here we present evidence for a C-terminally truncated form of the native binding protein in the plasma of subjects suffering from rheumatoid arthritis, which may parallel the in vitro truncation.
Woods
R J
RJ
School of Animal and Microbial Sciences, University of Reading, Whiteknights, United Kingdom.
Kemp
C F
CF
David
J
J
Lowry
P J
PJ
D000818:Animals; D001172:Arthritis, Rheumatoid / Q000097:blood*; D016466:CHO Cells; D002352:Carrier Proteins / Q000097:blood*; D006224:Cricetinae; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D015592:Immunoradiometric Assay; D008297:Male; D010446:Peptide Fragments / Q000097:blood; D011480:Protease Inhibitors / Q000494:pharmacology; D011489:Protein Denaturation; D011863:Radioimmunoassay; D011994:Recombinant Proteins; D014508:Urea / Q000494:pharmacology
D002352:Carrier Proteins; D010446:Peptide Fragments; D011480:Protease Inhibitors; D011994:Recombinant Proteins; C067133:corticotropin releasing factor-binding protein; D014508:Urea