N-Glycosylation Site in the Middle Region Is Involved in the Sperm-Binding Activity of Bovine Zona Pellucida Glycoproteins ZP3 and ZP4.

Mammalian fertilization is a species-selective event that involves a series of interactions between sperm proteins and the oocyte's zona pellucida (ZP) glycoproteins. Bovine ZP consists of three glycoproteins: bZP2, bZP3, and bZP4. In our previous study, we demonstrated that bovine sperm binds to plastic wells coated with recombinant bZP4 and identified that the N-terminal domain and the middle region of bZP4 are critical for sperm-binding activity. Here, we investigated the sperm-binding site in the middle region (residues 290 to 340) of bZP4, which includes the hinge region. We showed that bovine sperm binds to bZP4's middle region in a species-selective manner. We mapped the function of bZP4's middle region to its N-glycosylation site at Asn-314 using several recombinant mutated proteins. Moreover, we showed that mutations of the N-glycosylation sites at Asn-314 close to the hinge region and Asn-146 of the hinge region of bZP4 and bZP3, respectively, reduced the sperm-binding activity of the complex of the bZP3 (from 32 to 178) and bZP4 (from 136 to 464) fragments. Together, these results suggest that ZP's middle regions of bZP3 and bZP4 form one of the sperm-binding sites of bovine ZP.

Identification of Sperm-Binding Sites in the N-Terminal Domain of Bovine Egg Coat Glycoprotein ZP4.

The species-selective interaction between sperm and egg at the beginning of mammalian fertilisation is partly mediated by a transparent envelope called the zona pellucida (ZP). The ZP is composed of three or four glycoproteins (ZP1-ZP4). The functions of the three proteins present in mice (ZP1-ZP3) have been extensively studied. However, the biological role of ZP4, which was found in all other mammals studied so far, has remained largely unknown. Previously, by developing a solid support assay system, we showed that ZP4 exhibits sperm-binding activity in bovines and the N-terminal domain of bovine ZP4 (bZP4 ZP-N1 domain) is a sperm-binding region. Here, we show that bovine sperm bind to the bZP4 ZP-N1 domain in a species-selective manner and that N-glycosylation is not required for sperm-binding activity. Moreover, we identified three sites involved in sperm binding (site I: from Gln-41 to Pro-46, site II: from Leu-65 to Ser-68 and site III: from Thr-108 to Ile-123) in the bZP4 ZP-N1 domain using chimeric bovine/porcine and bovine/human ZP4 recombinant proteins. These results provide in vitro experimental evidence for the role of the bZP4 ZP-N1 domain in mediating sperm binding to the ZP.

Off-axis rotor in Enterococcus hirae V-ATPase visualized by Zernike phase plate single-particle cryo-electron microscopy.

EhV-ATPase is an ATP-driven Na+ pump in the eubacteria Enterococcus hirae (Eh). Here, we present the first entire structure of detergent-solubilized EhV-ATPase by single-particle cryo-electron microscopy (cryo-EM) using Zernike phase plate. The cryo-EM map dominantly showed one of three catalytic conformations in this rotary enzyme. To further stabilize the originally heterogeneous structure caused by the ATP hydrolysis states of the V1-ATPases, a peptide epitope tag system was adopted, in which the inserted peptide epitope sequence interfered with rotation of the central rotor by binding the Fab. As a result, the map unexpectedly showed another catalytic conformation of EhV-ATPase. Interestingly, these two conformations identified with and without Fab conversely coincided with those of the minor state 2 and the major state 1 of Thermus thermophilus V/A-ATPase, respectively. The most prominent feature in EhV-ATPase was the off-axis rotor, where the cytoplasmic V1 domain was connected to the transmembrane Vo domain through the off-axis central rotor. Furthermore, compared to the structure of ATP synthases, the larger size of the interface between the transmembrane a-subunit and c-ring of EhV-ATPase would be more advantageous for active ion pumping.

L-allo-threonine aldolase with an H128Y/S292R mutation from Aeromonas jandaei DK-39 reveals the structural basis of changes in substrate stereoselectivity.

L-allo-Threonine aldolase (LATA), a pyridoxal-5'-phosphate-dependent enzyme from Aeromonas jandaei DK-39, stereospecifically catalyzes the reversible interconversion of L-allo-threonine to glycine and acetaldehyde. Here, the crystal structures of LATA and its mutant LATA_H128Y/S292R were determined at 2.59 and 2.50 Šresolution, respectively. Their structures implied that conformational changes in the loop consisting of residues Ala123-Pro131, where His128 moved 4.2 Šoutwards from the active site on mutation to a tyrosine residue, regulate the substrate specificity for L-allo-threonine versus L-threonine. Saturation mutagenesis of His128 led to diverse stereoselectivity towards L-allo-threonine and L-threonine. Moreover, the H128Y mutant showed the highest activity towards the two substrates, with an 8.4-fold increase towards L-threonine and a 2.0-fold increase towards L-allo-threonine compared with the wild-type enzyme. The crystal structures of LATA and its mutant LATA_H128Y/S292R reported here will provide further insights into the regulation of the stereoselectivity of threonine aldolases targeted for the catalysis of L-allo-threonine/L-threonine synthesis.

Expression, purification, crystallization and preliminary X-ray analysis of 4-hydroxy-3-methyl-2-keto-pentanoate aldolase (asHPAL) from Arthrobacter simplex strain AKU 626.

4-Hydroxy-3-methyl-2-keto-pentanoate aldolase (asHPAL), an enzyme used in the synthesis of (2S,3R,4S)-4-hydroxyisoleucine, was crystallized in the absence and the presence of 2-ketobutyrate as one of its substrates by the sitting-drop vapour-diffusion method using PEG 400 as a precipitant. Crystals of asHPAL grown without and with 2-ketobutyrate diffracted to 1.60 and 1.55 Šresolution and belonged to space group C2, with unit-cell parameters a = 116.8, b = 88.2, c = 85.3 Å, ß = 122.3° and a = 116.2, b = 88.1, c = 85.0 Å, ß = 122.3°, respectively.

Crystallization and preliminary X-ray analysis of the haloalkane dehalogenase DatA from Agrobacterium tumefaciens C58.

Haloalkane dehalogenases are enzymes that catalyze the hydrolytic reaction of a wide variety of haloalkyl substrates to form the corresponding alcohol and hydrogen halide products. DatA from Agrobacterium tumefaciens C58 is a haloalkane dehalogenase that has a unique pair of halide-binding residues, asparagine (Asn43) and tyrosine (Tyr109), instead of the asparagine and tryptophan that are conserved in other members of the subfamily. DatA was expressed in Escherichia coli, purified and crystallized using the sitting-drop vapour-diffusion method with a reservoir solution consisting of 0.1 M CHES pH 8.6, 1.0 M potassium sodium tartrate, 0.2 M lithium sulfate, 0.01 M barium chloride. X-ray diffraction data were collected to 1.70 Å resolution. The space group of the crystal was determined as the primitive tetragonal space group P422, with unit-cell parameters a = b = 123.7, c = 88.1 Å. The crystal contained two molecules in the asymmetric unit.

Expression, purification, crystallization and preliminary X-ray analysis of carbonyl reductase S1 from Candida magnoliae.

The NADPH-dependent carbonyl reductase S1 from Candida magnoliae stereoselectively catalyzes the reduction of ethyl 4-chloro-3-oxobutanoate (COBE) to ethyl (S)-4-chloro-3-hydroxybutanoate (CHBE), which is a chiral compound valuable as a building block for pharmaceuticals. Carbonyl reductase S1 was expressed in Escherichia coli and purified by Ni-affinity, ion-exchange and size-exclusion chromatography. Crystals of carbonyl reductase S1 were obtained by the sitting-drop vapour-diffusion method using PEG 400 as a precipitant. X-ray diffraction data were collected to 1.90 Šresolution using a synchrotron-radiation source. The crystals belonged to space group P6(1)22 or P6(5)22, with unit-cell parameters a = b = 77.7, c = 307.5 Å. The asymmetric unit contained two molecules of the protein, with a solvent content of 44.2%.

Structure of calcium-bound human S100A13 at pH 7.5 at 1.8 A resolution.

S100A13 is a member of the S100 family of EF-hand-containing calcium-binding proteins. S100A13 plays an important role in the secretion of fibroblast growth factor-1 and interleukin 1 alpha, two pro-angiogenic factors released by the nonclassical endoplasmic reticulum/Golgi-independent secretory pathway. The X-ray crystal structure of human S100A13 at pH 7.5 was determined at 1.8 A resolution. The structure was solved by molecular replacement and was refined to a final R factor of 19.0%. The structure revealed that human S100A13 exists as a homodimer with two calcium ions bound to each protomer. The protomer is composed of four alpha-helices (alpha(1)-alpha(4)), which form a pair of EF-hand motifs. Dimerization occurs by hydrophobic interactions between helices alpha(1) and alpha(4) and by intermolecular hydrogen bonds between residues from helix alpha(1) and the residues between alpha(2) and alpha(3) of both chains. Despite the high similarity of the backbone conformation in each protomer, the crystal structures of human S100A13 at pH 7.5 (this study) and at pH 6.0 [Li et al. (2007), Biochem. Biophys. Res. Commun. 356, 616-621] exhibit recognizable differences in the relative orientation ( approximately 2.5 degrees) of the protomers within the dimer and also remarkable differences in the side-chain conformations of several amino-acid residues.

Crystallization and preliminary X-ray analysis of human S100A13.

S100A13 is a member of the S100 family of EF-hand-containing calcium-binding proteins and plays an important role in the secretion of fibroblast growth factor-1 and interleukin 1alpha, two pro-angiogenic factors released by the endoplasmic reticulum/Golgi-independent non-classical secretory pathway. Human S100A13 was heterologously expressed in Escherichia coli, purified and crystallized by the hanging-drop vapour-diffusion method using PEG 3350 as the precipitant. The crystals diffracted X-rays from a synchrotron-radiation source to 1.8 A resolution and the space group was assigned as primitive orthorhombic P2(1)2(1)2(1).

Down-regulation of DMBT1 gene expression in human oral squamous cell carcinoma.

Deleted in malignant brain tumors 1 (DMBT1) gene was recently isolated on chromosome 10q25.3-26.1 and has been proposed as a putative candidate tumor suppressor for brain, esophageal, gastric, colorectal, and lung cancer. However, little is known about the association of DMBT1 with oral squamous cell carcinoma (OSCC). To study the role of DMBT1 gene in OSCC oncogenesis, we examined 9 OSCC derived cell lines and 45 primary OSCC tissue specimens with respective normal tissues. Semi-quantitative reverse transcriptase chain reaction (RT-PCR) analysis revealed down-regulation or deletion of DMBT1 expression in all of the 9 cell lines and in 18 (40%) of 45 primary OSCC tissues. Additionally, 57 OSCC tissue specimens were examined by immunohistochemical staining of protein showing down-regulation of DMBT1 protein in 31 (56.1%) of the 57 primary OSCC tissue specimens. To assess restoration of DMBT1 expression by demethylation of promoter region, the 9 cell lines were treated with 5-aza-2-deoxycytidine (5-Aza-C), one of the DNA demethylating agents. Six (66.7%) of 9 cell lines demonstrated restoration of DMBT1 expression after 5-Aza-C treatment. These results suggest that DMBT1 gene is involved in OSCC oncogenesis and/or progression and that methylation of promoter region is one of the important mechanisms suppressing the DMBT1 gene expression.

Activity of exoglycosidases in ejaculated spermatozoa of boar and bull.

The activity of exoglycosidases in extracts from freshly ejaculated boar and bull spermatozoa with 0.2% Brij-35/2% acetic acid was measured. The results show that beta-N-acetylhexosaminidase, beta-galactosidase and alpha-mannosidase are the major glycosidases; much higher levels of activity were found in boar spermatozoa than in bull spermatozoa. When compared on a per spermatozoon basis, the ratios of the activities of beta-N-acetylhexosaminidase, beta-galactosidase and alpha-mannosidase in boar spermatozoon relative to those in bull spermatozoon were approximately 13000:1, 1700:1 and 400:1, respectively. Liberation of these glycosidases from bull spermatozoa by treatment with phosphatidylinositol-specific phospholipase C (PI-PLC) was low, in contrast to liberation of alpha-mannosidase from boar spermatozoa previously found by the same means. The possibility that the exoglycosidases present in large amounts in boar spermatozoa play a role in the process of binding to the zona pellucida glycoprotein of the egg is discussed.