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SPINKL, a Kazal-type serine protease inhibitor-like protein purified from mouse seminal vesicle fluid, is able to inhibit sperm capacitation

M Lin, Department of Obstetrics and Gynecology, Mackay Memorial Hospital, Taipei, Taiwan - Republic of China
R Lee, Department of Obstetrics and Gynecology, Mackay Memorial Hospital, Taipei, Taiwan - Republic of China
Y Hwu, Department of Obstetrics and Gynecology, Mackay Memorial Hospital, Taipei, Taiwan - Republic of China
C Lu, Department of Medical Research, Mackay Memorial Hospital, Tamshui, Taiwan - Republic of China
S Chu, Department of Medical Research, Mackay Memorial Hospital, Tamshui, Taiwan - Republic of China
Y Chen, Department of Medical Research, Mackay Memorial Hospital, Tamshui, Taiwan - Republic of China
W Chang, Genomics Research Center, Academia Sinica, Taipei, Taiwan - Republic of China
S Li, Mackay Medicine, Nursing and Management College, Taipei, Taiwan - Republic of China

Correspondence: Sheng-Hsiang Li, Email: lsh{at}ms1.mmh.org.tw

Abstract

We report a secreted serine protease inhibitor Kazal-type-like (SPINKL) protein. The SPINKL protein was purified from mouse seminal vesicle secretions through a series of steps, including ion-exchange chromatography on a diethylaminoethyl-Sephacel column, gel filtration on a Sephadex G-75 column, and ion-exchange high-performance liquid chromatography on a Q strong anion exchange column. Further analysis identified several SPINKL proteins with various N-linked carbohydrates. The SPINKL protein has six conserved cysteine residues which are nearly identical to those of members of the serine protease inhibitor Kazal protein family. It was noted that the SPINKL protein showed no inhibitory activities against common serine proteases such as trypsin, chymotrypsin, subtilisin, or elastase. Spinkl mRNA and SPINKL proteins were found to primarily be expressed in seminal vesicles. Immunohistochemistry revealed that the SPINKL protein occurred in the luminal fluid and mucosal epithelium of the seminal vesicles and was regulated by testosterone. The SPINKL protein was able to bind onto sperm and enhance sperm motility. Also, it was able to suppress bovine serum albumin-stimulated sperm capacitation and block sperm-oocyte interactions in vitro, suggesting that SPINKL may be a decapacitation factor.