Prostate-specific antigen triggers transformation of seminal alpha2-macroglobulin (alpha2-M) and its binding to alpha2-macroglobulin receptor/low-density lipoprotein receptor-related protein (alpha2-M-R/LRP) on human spermatozoa.
BACKGROUND
The aim of this study was to identify the proteolytic activity which triggers the transformation of human alpha2-macroglobulin (alpha2-M) in seminal fluid and its binding to its receptor.


METHODS
Measurement of the concentrations of total and transformed alpha2-M in seminal fluid was accomplished by ELISA. Zymography of seminal plasma was performed in SDS-polyacrylamide gels containing casein as proteolytic substrate. Rate electrophoresis, SDS-PAGE, and Western blotting were applied to study the complex formation of prostate-specific antigen (PSA) with alpha-M. Ligand-binding analysis of sperm cells was performed using [125I] labeled proteins. Detection of receptor on sperm cells was achieved by immunofluorescence.


RESULTS
The mean concentration of total alpha2-M in a random collection of seminal plasma was 4.6 microg/ml. On average, between 33-98% of the inhibitor was found to be transformed. Zymography of seminal plasma revealed a proteolytic activity which is associated with a 33-kDa protein identified as PSA. Its proteolytic activity could be inhibited by 0.2-M. Both purified PSA and seminal plasma were capable of transforming native alpha2-M. Binding of PSA to alpha2-M triggers the exposition of receptor binding sites in the inhibitor molecule, which causes binding of the complex to alpha2-M-R/LRP identified on spermatozoa.


CONCLUSIONS
PSA, the main proteinase in seminal fluid, is responsible for the transformation of alpha2-M and for its binding to alpha2-M-R/LRP present on spermatozoa. The binding of alpha2-M-PSA complexes to the spermatozoa receptor may exert an impact on normal sperm-cell functions.
Birkenmeier
G
G
Institute of Biochemistry and Department of Andrology, University of Leipzig, Germany. birg@medizin.uni-leipzig.de
Usbeck
E
E
Schäfer
A
A
Otto
A
A
Glander
H J
HJ
D001665:Binding Sites; D006801:Humans; D066298:In Vitro Techniques; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D046911:Macromolecular Substances; D008297:Male; D017430:Prostate-Specific Antigen / Q000737:chemistry / Q000378:metabolism*; D011480:Protease Inhibitors / Q000378:metabolism; D011485:Protein Binding; D011971:Receptors, Immunologic / Q000378:metabolism*; D011973:Receptors, LDL / Q000378:metabolism*; D012661:Semen / Q000276:immunology / Q000378:metabolism*; D013091:Spermatogenesis / Q000502:physiology; D013094:Spermatozoa / Q000276:immunology / Q000378:metabolism* / Q000502:physiology; D000511:alpha-Macroglobulins / Q000737:chemistry / Q000378:metabolism*
D026503:Low Density Lipoprotein Receptor-Related Protein-1; D046911:Macromolecular Substances; D011480:Protease Inhibitors; D011971:Receptors, Immunologic; D011973:Receptors, LDL; D000511:alpha-Macroglobulins; D017430:Prostate-Specific Antigen