Sperm associated antigen 11 isoform A

Antimicrobial proteins and peptides are ubiquitous in nature with diverse structural and biological properties. Among them, the human beta-defensins are known to contribute to the innate immune response. Besides the defensins, a number of defensin-like proteins and peptides are expressed in many organ systems including the male reproductive system. Some of the protein isoforms encoded by the sperm associated antigen 11B (SPAG11) gene in humans are beta-defensin-like and exhibit structure dependent and salt tolerant antimicrobial activity, besides contributing to sperm maturation. Though some of the functional roles of these proteins are reported, the structural and molecular features that contribute to their antimicrobial activity is not yet reported. In this study, using in silico tools, we report the three dimensional structure of the human SPAG11B proteins and their C-terminal peptides. web-based hydropathy, amphipathicity, and topology (WHAT) analyses and grand average of hydropathy (GRAVY) indices show that these proteins and peptides are amphipathic and highly hydrophilic. Self-optimized prediction method with alignment (SOPMA) analyses and circular dichroism data suggest that the secondary structure of these proteins and peptides primarily contain beta-sheet and random coil structure and alpha-helix to a lesser extent. Ramachandran plots show that majority of the amino acids in these proteins and peptides fall in the permissible regions, thus indicating stable structures. The secondary structure of SPAG11B isoforms and their peptides were not perturbed with increasing NaCl concentration (0-300 mM) and at different pH (3, 7, and 10), thus reinforcing our previously reported observation that their antimicrobial activity is salt tolerant. To the best of our knowledge, for the first time, results of our study provide vital information on the structural features of SPAG11B protein isoforms and their contribution to antimicrobial activity.

Background: We undertook this study to investigate the variation relationship of sperm associated antigen 11 (Spag11) mRNA expression and SPAG11E protein in the epididymis and spermatozoa of experimental left varicocele (ELV) rats. These findings could contribute to the understanding of the role of epididymal proteins in sperm functions and the mechanism of male infertility induced by varicocele. Methods: The ELV model was established in adolescent male Sprague-Dawley rats. Four weeks after the operation, tissue distribution and changes in the expressions of Spag11 mRNA and SPAG11E protein caused by ELV in the whole of left epididymis and spermatozoa were studied using quantitative reverse transcription-polymerase chain reaction (RT-QPCR), immunohistochemistry and immunofluorescence. Significant differences were identified using one-way ANOVA followed by Student-Newman-Keuls test. Significance level (p) was fixed at 0.05. Results: The expected product of Spag11 was 96 bp that amplified by RT-QPCR was detected in the epididymal tissue and spermatozoa. SPAG11E protein was confined mainly to the supranuclear region of the principal cells and the stereocilium of the epididymal epithelium, it was concentrated on the acrosome and the tail of spermatozoa except the terminal piece. Statistical analyses of the images and the data indicated that Spag11 mRNA and SPAG11E protein expressions in the left epididymis and spermatozoa of ELV rats presented a considerable decrease (p<0.001) compared with that of the corresponding control group. Conclusion: The expressions of Spag11 mRNA and SPAG11E protein declined markedly in ELV rats, which suggest that SPAG11E may not only play an important role in sperm maturation, but it may also be influenced by varicocele.