In silicoanalysis of candidate proteins sharing homology withStreptococcus agalactiaeproteins and their role in male infertility

Abstract

Leukocytospermia is a physiologic condition defined as human semen with a leukocyte count of >1 x 10 6 cells/ml that is often correlated with male infertility. Moreover, bacteriospermia has been associated with leukocytospermia ultimately leading to male infertility. We have found that semen samples with >1 x 10 6 /ml leukocytes and/or bacteriospermia have oxidative predominance as evidenced by augmented protein carbonyl and lipid peroxidation status of the semen which is implicated in sperm dysfunction. It has been reported that Streptococcus agalactiae is present in bacteriospermic samples. Previous research has shown that human leukocyte antigen beta chain paralog (HLA-DRB) alleles interact best with the infected sperm cells rather than the non-infected cells. Little is known about the interaction of major histocompatibility complex (MHC) present on leukocytes with the sperm upon bacterial infection and how it induces an immunological response which we have addressed by epitope mapping. Therefore, we examined MHC class II derived bacterial peptides which might have human sperm-related functional aspects. Twenty-two S. agalactiae proteins were obtained from PUBMED protein database for our study. Protein sequences with more than two accession numbers were aligned using CLUSTAL Omega to check their conservation pattern. Each protein sequence was then analyzed for T-cell epitope prediction against HLA-DRB alleles using the immune epitope database (IEDB) analysis tool. Out of a plethora of peptides obtained from this analysis, peptides corresponding to proteins of interest such as DNA binding response regulator, hyaluronate lyase and laminin binding protein were screened against the human proteome using Blastp. Interestingly, we have found bacterial peptides sharing homology with human peptides deciphering some of the important sperm functions. Antibodies raised against these probable bacterial antigens of fertility will not only help us understand the mechanism of leukocytospermia/ bacteriospermia induced male factor infertility but also open new avenues for immunocontraception. Abbreviations: AA: amino acid; ASA: antisperm antibodies; GBS: group B streptococcus; HLA: human leukocyte antigen; HAS3: hyaluronan synthase 3: IEDB: immune epitope database; MAPO2: O 6 -methylguanine-induced apoptosis 2; MHC: major histocompatibility complex; ROS: reactive oxygen species; Rosbin1: round spermatid basic protein 1; S. agalactiae: Streptococcus agalactiae; SA: sperm antigen; SPATA17: spermatogenesis associated protein17; SPNR: spermatid perinuclear RNA binding protein; TEX15: testis-expressed sequence 15 protein; TOPAZ: testis-and ovaryspecific PAZ domain-containing protein; TPABP: testis-specific poly-A binding protein; TPAP: testis-specific poly(A) polymerase; WHO: World Health Organization ARTICLE HISTORY

Human MOSPD2: A bacterial Lmb mimicked auto-antigen is involved in immune infertility

“…Since the partial sequence of the putative self-antigen, MOSPD2 derived from S. agalactiae specific Lmb protein showed resemblance with the Lbp protein of S. pyogenes [1] , [43] , S. pyogenes was selected as a control bacteria model to study the effect of Lmb mimicked MOSPD2 self-peptide in the seminal plasma containing ASAs. Pure bacterial strain of S. pyogenes MTCC no.…”

“…The sequence of the Lmb mimicked MOSPD2 antigen was obtained from the in silico analysis of S. agalactiae Lmb protein [1] . The FASTA sequence of the Lmb protein sequence with 287 residues (20–306 amino acids) used in this study was aligned pair-wise with the original sequence of the Lmb protein (pdb id 3HJT ) containing 306 residues obtained from the crystallography study [43] .…”

“…Based on the selection criteria mentioned in our previous publication [1] , in silico analysis was carried out for gram-positive bacteria E. faecalis and S. aureus, predominantly present in the semen along with S. agalactiae, to determine the MOSPD2 antigens. Mainly surface/membrane proteins were targeted.…”

“…However, validation of such derivation is a cumbersome task. Previously we have recognized human motile sperm domain-containing protein 2 (MOSPD2) as a putative self-antigen through in silico analysis [1] . This self-antigen with the partial sequence ‘ KDSYTKKAKAFKKEA’ was derived from the Streptococcus agalactiae specific Laminin binding protein (Lmb) by using T-cell epitope mapping and bears the ability to bind with the HLA-DRB allele.…”

“…Though a large number of proteins are identified as cognate antigens for the production of ASAs, the ones that possess major hindrance to sperm functional goals, particularly fertilization, is not yet elucidated [32] , [34] . Thus, the curiosity to ensure ASA producing self-antigens in the semen has led to the derivation of a putative self-peptide showing similarity with human motile sperm domain-containing protein 2 (MOSPD2) from the seminal bacteria Streptococcus agalactiae (a Group B Streptococcus or, GBS) and Streptococcus pyogenes [1] . This study will not only help in the management of infertility in men but also, pave way for the development of potent immunocontraception for men.…”