We previously established an anti-mouse sperm auto-monoclonal antibody, Ts4, which shows immunoreactivity against several kinds of glycoproteins in the acrosomal region of epididymal spermatozoa, testicular germ cells, and early embryo, via binding to an epitope containing a common N-linked oligosaccharide (OS) chain on the molecules. In mice, we have already demonstrated that the OS chain in the epitope for Ts4 is a fucosylated agalacto-complex-type biantennary glycan carrying bisecting N-acetylglucosamine. In the testis, one of the specific OS chain-conjugated molecules is TEX101, a germ cell-marker glycoprotein, which is expressed in spermatocytes, spermatids, and testicular spermatozoa, but not in epididymal spermatozoa. In this study, we identified a Ts4-reactive glycoprotein in mouse cauda epididymal sperm. An immunoprecipitation method together with liquid chromatography-tandem mass spectrometry showed that alpha-N-acetylglucosaminidase (Naglu; a degradation enzyme of heparan sulfate) is one of the glycoproteins recognized by Ts4 in the epididymal spermatozoa. Western blot and immunohistochemical analyses revealed that mouse Naglu exists in two forms (82 and 77 kDa) and is expressed in the acrosomal region and the flagellum of cauda epididymal sperm. Of the two Nagluforms expressed in sperm, Ts4 immunoreacted against only the 82-kDa form located on the acrosomal region. The Ts4 mAb and anti-Naglu pAb negatively affected mouse fertilization in vitro. In addition, Ts4 inhibited sperm acrosome reaction induced by heparan sulfate. The Ts4-recognized fucosylated agalactobiantennary complex-type glycan with bisecting N-acetylglucosamine and Naglu on cauda epididymal spermatozoa may play a role in the process of fertilization. (C) 2016 Elsevier Ireland Ltd. All rights reserved.