title: Purification, structure and partial characterization of the major sperm activating protein complex in human serum.
abstract: Serum has long been known to enhance sperm motility, and the major factor that mediates this activation has been shown to be a macromolecule complex with a MW of about 250 kD. This macromolecule, named Sperm Activating Protein (SPAP) has now been purified by a four step protocol. Starting with 100 mL of serum 20 to 200 micrograms of purified SPAP was recovered (N = 40). Studies on the identification and structure of SPAP revealed that the macromolecule is formed by an IgG molecule to which an apolipoprotein A-I molecule is bound. Further studies on the structure of the complex was performed by partial proteolytic cleavage of SPAP by pepsin and papain and interaction with poly- and monoclonal antibodies. Based on these results the most plausible structure of SPAP places one molecule of apo A-I between the two arms of the Fab portion of an IgG4 molecule. Human spermatozoa incubated with polyclonal anti-SPAP serum and a second FITC-labelled antiserum showed fluorescence at a distinct band at the lower part of the sperm head, indicating that SPAP acts by direct interaction with the spermatozoa. The SPAP molecule shows a new mechanism mediated by the immunoglobulins, that may be very important for male fecundity.
authors.affiliation: Department of Clinical Chemistry, Karolinska Institutet, Huddinge University Hospital, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Pousette
authors.forename: P K
authors.initials: PK
authors.lastname: Leijonhufvud
authors.forename: E
authors.initials: E
authors.lastname: Akerlöf
mesh_terms: D016632:Apolipoprotein A-I / Q000032:analysis / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism; D015153:Blotting, Western; D002845:Chromatography; D004591:Electrophoresis, Polyacrylamide Gel; D005455:Fluorescent Antibody Technique; D006801:Humans; D007074:Immunoglobulin G / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D008297:Male; D008958:Models, Molecular; D013081:Sperm Motility / Q000187:drug effects; D013094:Spermatozoa / Q000737:chemistry* / Q000378:metabolism
chemical_list: D016632:Apolipoprotein A-I; D007074:Immunoglobulin G