Fibrinogen‐related protein, FGL2, of hamster cauda epididymal fluid: Purification, kinetic analysis of its prothrombinase activity, and its role in segregation of nonviable spermatozoa

Fibrinogen‐related protein, FGL2, of hamster cauda epididymal fluid: Purification, kinetic analysis of its prothrombinase activity, and its role in segregation of nonviable spermatozoa

Although the epididymal environment promotes the maturation and survival of spermatozoa, not all spermatozoa remain viable during passage through the epididymis. Does the epididymis has a protective mechanism(s) to segregate the viable sperm from defective spermatozoa? Previously, we identified 260/...

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Published in:Molecular reproduction and development Vol. 87; no. 12; pp. 1206 - 1218
Main Authors: Nagdas, Subir K., Wallace, Shamar, Eaford, Don, Baker, Rashad, Carr, Ky'ara, Raychoudhuri, Samir S.
Format: Journal Article
Language:English
Published: United States Wiley Subscription Services, Inc 01-12-2020
Subjects:
Epididymis
Fibrinogen
fibrinogen‐like protein‐2 (FGL2)
hamster sperm
Immunoprecipitation
Polypeptides
Population studies
Protein purification
Proteins
Prothrombin
Prothrombinase
Serine
Serine proteinase
Sperm
Thrombin
ubiquitination
fibrinogen-like protein-2 (FGL2)
epididymis
prothrombinase
ubiquitination
hamster sperm
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Summary:Although the epididymal environment promotes the maturation and survival of spermatozoa, not all spermatozoa remain viable during passage through the epididymis. Does the epididymis has a protective mechanism(s) to segregate the viable sperm from defective spermatozoa? Previously, we identified 260/280 kDa oligomers (termed eFGL—Epididymal Fibrinogen‐Like oligomer) are composed of two disulfide‐linked subunits: a 64 kDa polypeptide identified as fibrinogen‐like protein‐2 (FGL2) and a 33 kDa polypeptide identified as fibrinogen‐like protein‐1 (FGL1). Our morphological studies demonstrated that the eFGL, secreted from the principal cells of the cauda epididymis, is polymerized into a death cocoon‐like complex (DCF), masking defective luminal spermatozoa but, not the viable sperm population. In the present study, we purified FGL2 from hamster cauda epididymal fluid toward homogeneity and its prothrombinase catalytic activity was examined. Time‐course conversion studies revealed that all prothrombin was converted to thrombin by purified hamster FGL2. Our biochemical studies demonstrate that FGL2 is a lipid‐activated serine protease and functions as a lectin by binding specific carbohydrate residues. Co‐immunoprecipitation analysis demonstrated that FGL2 of cauda epididymal fluid is ubiquitinated but not the FGL1. We propose that FGL2/FGL1 oligomers represent a novel and unique mechanism to shield the viable sperm population from degenerating spermatozoa contained within the tubule lumen.
Bibliography:Author Contribution Statement: Each authors have contributions to the article.
ISSN:1040-452X
1098-2795
DOI:10.1002/mrd.23438