Crystal structure of Sperm Lysozyme-Like Protein 1 (SLLP1) and database for structural-functional studies

HEPING ZHENG SLLP1 is a non-bacteriolytic, c-lysozyme-like protein in mammalian sperm acrosome and shows specific expression in testis. Antisera to SLLP1 block binding in the hamster egg penetration assay, indicating its possible role in sperm-egg adhesion. SLLP1 receptor on egg plasma membrane (SAS1R) is identified by mass spectrometry, coimmunoprecipitation and far-western analysis. Recombinant SLLP1 protein binds to the egg membrane, and co-localizes with SAS1R in immuno-fluorescence assay. Mouse SLLP1 (mSLLP1) structure was solved by molecular replacement to 2.3 Å resolution and refined to an R factor of 19.7%. SLLP1 shows a similar fold to lysozyme with all four disulfide bonds conserved. A similar oligosaccharide binding groove in lysozyme is also observed in mSLLP1 structure. The groove is formed mostly by hydrophilic and acidic residues. While one wall of the channel is well ordered, the other wall, where the aromatic ring of Tyr108 protrudes into the groove, is highly mobile and could readily move to accommodate bound ligand in the channel. SLLP1 binding specificity was investigated using various experimental methods including glycoarray analysis with 320 different oligosaccharides, yet no binding was detected. SLLP1 model was used for virtual screening using docking program, which identified a potential ligand (mannosyl)paromomycin with a binding desolvation energy of around 15 kcal / mol by MM-PBSA analysis. Several bioinformatics tools were developed for SLLP1 functional site analysis, but have wider application. A binding site study was carried out to assess the correct prediction of the functional site of an apo-structure. NEIGHBORHOOD is a database of protein molecular structures that can be used for search and identification of functional site, as well as their comparison and analysis. This database stores the vicinity information as a collection of restraints for all potential inter-residue interactions, which consequently allows for the search of a specific spatial arrangement of amino acid in protein structures. Results can be further refined by parameters and outcomes of experimental setup, which allows us to restrict our query to a specific problem of interest. NEIGHBORHOOD database was used in the analysis of metal binding sites in metalloproteins, providing key information for identification and refinement of metal binding sites.

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