Abstract
Human seminal plasma contains a factor that binds human IgG, designated as immunoglobulin binding factor (IgBF). Under reducing condition IgBF interacts with anti-Leu-11b, a murine monoclonal antibody raised against human FcγRIII/CD16. IgBF shows no binding activity under non-reducing condition. Three components having IgBF activity were separated by HPLC and their amino acid sequences determined. The main IgBF showed structural identity to β-microseminoprotein (β-MSP), prostatic secretory protein of 94 amino acids (PSP94) and β-inhibin. The slight variation in the reported sequences of these proteins has been attributed to analytical error. In the present study the molecular masses of main IgBF and β-MSP/PSP94 were found to be identical by mass spectrometry. In addition, a large component of IgBF and a shorter β-MSP consisting of 93 amino acids were identified. The binding of β-MSP for human IgG and anti-Leu-11b antibody is demonstrable only under reducing condition, determined by Western blot analysis. The present data clearly show that IgBF is a family composed of at least three isoforms. One of the members is β-MSP/PSP94. This family should be designated as IgBF.
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Schedule a callMore From: Biochimica et Biophysica Acta (BBA)/Protein Structure and Molecular Enzymology
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