Characterization and In Silico Analysis of Pregnancy-Associated Glycoprotein-1 Gene of Buffalo (Bubalus bubalis)

Buffalo early pregnancy biomarker coding sequence cloning and partial length expression in E. coli after codon optimization

Pregnancy-associated glycoproteins (PAGs) secreted from conceptus specific trophoblast cells are widely accepted biomarkers of ruminants. Limited information of PAGs in buffalo warrants further investigation for the development of sensitive homologous early pregnancy-specific diagnostic immunoassay. This experiment was thus designed to identify and clone the predominantly expressed early placentome-specific buffalo PAG (buPAG) isoform; to express this PAG isoform and verify its antigenicity by developing antisera and testing immuno-reactivity with recombinant proteins. Results indicated PAG 7 (buPAG 7) was the predominant isoform in buffalo early pregnant placentome. Attempt to express the full native glycosylated protein in the pcDNA3.3 vector and FreeStyle HEK 293F host was not successful. However, a partial 124 amino acid sequence selected from the non-glycosylated region of buPAG 7 could be expressed in E. coli BL21 (DE3) cells after codon optimization however; the yield was low. Antigenicity of the expressed protein was confirmed by successful immuno-reaction in rabbits indicating possibilities of using 124 aa partial PAG 7 protein as a putative antigen for monoclonal antibody production and development sensitive homologous immunoassay. In conclusion, our results confirmed the findings that buPAG 7 as the predominant early pregnancy-specific transcript. A selected partial 124 amino acid sequences of it could even be expressed in a heterologous host (E. coli). Based on our data presented here, we anticipate that the expressed recombinant protein can be useful as an antigen suitable for the development of PAG specific immunoassays in buffalo.

Purification of pregnancy-associated glycoproteins from late-pregnancy Bubalus bubalis placentas and development of a radioimmunoassay for pregnancy diagnosis in water buffalo females

Background

Pregnancy-associated glycoproteins (PAGs) were first described as placental antigens present in the blood serum of the mother soon after implantation. Here, we describe the purification of several pregnancy-associated glycoproteins from water buffalo placenta (wbPAGs). A specific radioimmunoassay (RIA) was developed for early pregnancy diagnosis in buffalo species.

Results

Amino-terminal microsequencing of immunoreactive placental proteins allowed the identification of eleven wbPAGs sequences [Swiss-Prot accession numbers: P86369 to P86379]. Three polyclonal antisera (AS#858, AS#859 and AS#860) were raised in rabbits against distinct wbPAG fractions. A new RIA (RIA-860) was developed and used to distinguish between pregnant (n = 33) and non-pregnant (n = 26) water buffalo females.

Conclusions

Our results confirmed the multiplicity of PAG expression in buffalo placenta. In addition, the RIA-860 system was shown to be sensitive, linear, reproducible, accurate and specific in measuring PAG concentrations in buffalo plasma samples from Day 37 of gestation onwards.

Structural Modeling and Analysis of Pregnancy-Associated Glycoprotein-1 of Buffalo (Bubalus bubalis)

The present study was conducted to design and analyze the structural model of buffalo pregnancy-associated glycoprotein-1 (PAG-1) using bioinformatics. Structural modeling of the deduced buffalo PAG-1 protein was done using PHYRE, CONSURF servers and its structure was subsequently constructed using MODELLER 9.9 and PyMOL softwares Buffalo PAG-1 structural conformity was analyzed using PROSA, WHATIF, and 3D-PSSM servers. Designed buffalo PAG-1 protein structure on BLAST analysis retrieved protein structures belonging to aspartic proteinase family. Moreover in silico analysis revealed buffalo PAG-1 protein retained bilobed structure with pepstatin-binding clefts near the active sites by docking studies with pepstatin A using PatchDock server. Structural studies revealed that the amino and carboxy terminal containing aspartic residues are highly conserved and buried within the protein structure. Structural conformity studies showed that more than 90% of the residues lie inside favored and allowed regions. It was also deduced that buffalo PAG-1 possesses low and high energy zones with a very low threshold for proteolysis ascertaining the stableness of the buffalo PAG-1 protein structure. This study depicts the structural conformity and stability of buffalo PAG-1 protein.