Cloning, expression, characterization and crystallization of BRP39, a signalling glycoprotein expressed during mammary gland apoptosis

A novel humanized Chi3l1 blocking antibody attenuates acetaminophen-induced liver injury in mice

Acetaminophen (APAP) overdose is a leading cause of acute liver injury in the USA. The chitinase 3-like-1 (Chi3l1) protein contributes to APAP-induced liver injury (AILI) by promoting hepatic platelet recruitment. Here, we report the development of a Chi3l1-targeting antibody as a potential therapy for AILI. By immunizing a rabbit successively with the human and mouse Chi3l1 proteins, we isolated cross-reactive monoclonal antibodies (mAbs) from single memory B cells. One of the human and mouse Chi3l1 cross-reactive mAbs was humanized and characterized in both in vitro and in vivo biophysical and biological assays. X-ray crystallographic analysis of the lead antibody C59 in complex with the human Chi3l1 protein revealed that the kappa light contributes to majority of the antibody-antigen interaction; and that C59 binds to the 4α-5β loop and 4α-helix of Chi3l1, which is a functional epitope and hotspot for the development of Chi3l1 blocking antibodies. We humanized the C59 antibody by complementarity-determining region grafting and kappa chain framework region reverse mutations. The humanized C59 antibody exhibited similar efficacy as the parental rabbit antibody C59 in attenuating AILI in vivo. Our findings validate Chi3l1 as a potential drug target for AILI and provide proof of concept of developing Chi3l1 blocking antibody as a therapy for the treatment of AILI.

Crystal structure of breast regression protein 39 (BRP39), a signaling glycoprotein expressed during mammary gland apoptosis, at 2.6 Å resolution

Breast regression protein 39 (BRP39) is a 39 kDa protein that is a member of chitolectin class of glycosyl hydrolase family 18 (GH18). High expression levels of BRP39 have been detected in breast carcinoma. It helps in proliferation of cells during the progression of this disease and may act as a signaling factor. BRP39 may act as a potential candidate for rational structure-based drug design against breast carcinoma. In this study, we report the crystal structure of mouse recombinant BRP39 expressed in E. coli. The structure was solved by molecular replacement and refined to 2.6 Å resolution. The overall structure of BRP39 consisted of two globular domains: a large (β/α)₈ triosephosphate isomerase (TIM) barrel domain and a small (α + β) domain. Three non-proline cis-peptides were detected in the sugar-binding cleft of BRP39, including Ser57-Phe58, Leu141-Tyr142, and Trp353-Ala354. The latter residues were conserved in other GH18 family members. It was notable that the conformation of critical Trp100 residue within the sugar-binding cleft was oriented away from the barrel. The side-chain conformation was found to be similar to that observed in chitinases, however, it was oriented into the barrel in other chitinase-like proteins (CLPs). The conformation of this critical residue may have significant implications in sugar binding. Further, two amino acid substitutions were observed in the sugar-binding groove of BRP39. The conserved Asn100 and Arg263 in Hcgp39 and other CLPs proteins (SPX-40 structures) were substituted by Lys101 and Lys264 in BRP39 which may have a significant impact on the sugar-binding properties.

Structural and functional characterization of buffalo oviduct-specific glycoprotein (OVGP1) expressed during estrous cycle

Oviduct-specific glycoprotein (OVGP1) is a high molecular weight chitinase-like protein belonging to GH18 family. It is secreted by non-ciliated epithelial cells of oviduct during estrous cycle providing an essential milieu for fertilization and embryo development. The present study reports the characterization of buffalo OVGP1 through structural modeling, carbohydrate-binding properties and evolutionary analysis. Structural model displayed the typical fold of GH18 family members till the boundary of chitinase-like domain further consisting of a large (β/α)₈ TIM barrel sub-domain and a small (α+β) sub-domain. Two critical catalytic residues were found substituted in the catalytic centre (Asp to Phe118, Glu to Leu120) compared with the active chitinase. The carbohydrate-binding groove in TIM barrel was lined with various conserved aromatic residues. Molecular docking with different sugars revealed the involvement of various residues in hydrogen-bonding and non-bonded contacts. Most of the substrate-binding residues were conserved except for a few replacements (Ser13, Lys48, Asp49, Pro50, Asp167, Glu199, Gln272 and Phe275) in comparison with other GH18 members. The residues Trp10, Trp79, Asn80, Gln272, Phe275 and Trp334 were involved in recognition of all six ligands. The α+β sub-domain participated in sugar-binding through Thr270, Gln272, Tyr242 and Phe275. The binding assays revealed significant sugar-binding with purified native and recombinant OVGP1. Phylogenetic analysis revealed that OVGP1 was closely related to AMCases followed by other CLPs and evolution of OVGP1 occurred through several gene duplications. This is the first study describing the structural characteristics of OVGP1 that will further help to understand its interaction with gametes to perform crucial reproductive functions.

The Multifaceted Role of STAT3 in Mammary Gland Involution and Breast Cancer

Since seminal descriptions of signal transducer and activator of transcription 3 (STAT3) as a signal transducer and transcriptional regulator, which is most usually activated by phosphorylation of a specific tyrosine residue, a staggering wealth of research has delineated the key role of this transcription factor as a mediator of mammary gland postlactational regression (involution), and paradoxically, a pro-survival factor in breast cancer and some breast cancer cell lines. STAT3 is a critical regulator of lysosomal-mediated programmed cell death (LM-PCD) during mammary gland involution, where uptake of milk fat globules, and consequent high levels of free fatty acids, cause permeabilisation of lysosomal vesicle membranes, in turn leading to cathepsin protease leakage and cell death. A recent proteomic screen of STAT3-induced changes in lysosomal membrane protein components has highlighted wide-ranging effects of STAT3, which may coordinate LM-PCD via the stimulation of endocytosis, intracellular trafficking, and lysosome biogenesis. In parallel, STAT3 regulates the acute phase response during the first phase of involution, and it contributes to shaping the pro-tumourigenic 'wound healing' signature of the gland during the second phase of this process. STAT3 activation during involution is important across species, although some differences exist in the progression of involution in dairy cows. In breast cancer, a number of upstream regulators can lead to STAT3 activation and the effects of phosphorylation of STAT3 are equally wide-ranging. Recent studies have implicated microRNAs in some regulatory pathways. In this review, we will examine the multifaceted role of STAT3 in mammary gland involution and tumourigenesis, incorporating a review of these fundamental processes in tandem with a discussion of recent developments in this field.

Paternal RLIM/Rnf12 is a survival factor for milk-producing alveolar cells

In female mouse embryos, somatic cells undergo a random form of X chromosome inactivation (XCI), whereas extraembryonic trophoblast cells in the placenta undergo imprinted XCI, silencing exclusively the paternal X chromosome. Initiation of imprinted XCI requires a functional maternal allele of the X-linked gene Rnf12, which encodes the ubiquitin ligase Rnf12/RLIM. We find that knockout (KO) of Rnf12 in female mammary glands inhibits alveolar differentiation and milk production upon pregnancy, with alveolar cells that lack RLIM undergoing apoptosis as they begin to differentiate. Genetic analyses demonstrate that these functions are mediated primarily by the paternal Rnf12 allele due to nonrandom maternal XCI in mammary epithelial cells. These results identify paternal Rnf12/RLIM as a critical survival factor for milk-producing alveolar cells and, together with population models, reveal implications of transgenerational epigenetic inheritance.

Analyzing airway inflammation with chemical biology: dissection of acidic mammalian chitinase function with a selective drug-like inhibitor

Acidic mammalian chitinase (AMCase) is produced in the lung during allergic inflammation and asthma, and inhibition of enzymatic activity has been considered as a therapeutic strategy. However, most chitinase inhibitors are nonselective, additionally inhibiting chitotriosidase activity. Here, we describe bisdionin F, a competitive AMCase inhibitor with 20-fold selectivity for AMCase over chitotriosidase, designed by utilizing the AMCase crystal structure and dicaffeine scaffold. In a murine model of allergic inflammation, bisdionin F-treatment attenuated chitinase activity and alleviated the primary features of allergic inflammation including eosinophilia. However, selective AMCase inhibition by bisdionin F also caused dramatic and unexpected neutrophilia in the lungs. This class of inhibitor will be a powerful tool to dissect the functions of mammalian chitinases in disease and represents a synthetically accessible scaffold to optimize inhibitory properties in terms of airway inflammation.

Purification, sequence characterization and effect of goat oviduct-specific glycoprotein on in vitro embryo development

Oviduct-specific glycoprotein (oviductin) plays an important role during fertilization and early embryonic development. The oviductin cDNA was successfully cloned and sequenced in goat, which possessed an open reading frame of 1620 nucleotides representing 539 amino acids. Predicted amino acid sequence showed very high identity with sheep (97%) followed by cow (94%), porcine (77%), hamster (69%), human (66%), rabbit (65%), mouse (64%) and baboon (62%). The bioinformatics analysis of the sequences revealed the presence of a signal sequence of 21 amino acids, one potential N-linked glycosylation site at position 402, 21 potential O-linked glycosylation sites and 36 potential phosphorylation sites. The native oviductin was purified from the oviductal tissue, which showed three distinct bands on SDS-PAGE and western blot (MW ~60-95 kDa). The predicted molecular weight of goat oviductin was 57.5 kDa, calculated from the amino acid sequences. The observed higher molecular weight has been attributed to the presence of large number of potential O-linked glycosylation sites. The lower concentration (10 μg/mL) of oviductin increased the cleavage rate, morula and blastocyst yield significantly (P < 0.05) as compared to higher concentration (100 μg/mL). Goat oviductin retarded the activity of pronase (0.1%) on zona solubility of oocytes significantly (P < 0.01).

Application of protein engineering to enhance crystallizability and improve crystal properties

Until recently, protein crystallization has mostly been regarded as a stochastic event over which the investigator has little or no control. With the dramatic technological advances in synchrotron-radiation sources and detectors and the equally impressive progress in crystallographic software, including automated model building and validation, crystallization has increasingly become the rate-limiting step in X-ray diffraction studies of macromolecules. However, with the advent of recombinant methods it has also become possible to engineer target proteins and their complexes for higher propensity to form crystals with desirable X-ray diffraction qualities. As most proteins that are under investigation today are obtained by heterologous overexpression, these techniques hold the promise of becoming routine tools with the potential to transform classical crystallization screening into a more rational high-success-rate approach. This article presents an overview of protein-engineering methods designed to enhance crystallizability and discusses a number of examples of their successful application.