Development of a novel monoclonal antibody-based competitive ELISA for antibody detection against bovine leukemia virus

Infection with bovine leukemia virus (BLV) leads to enzootic bovine leukosis, the most prevalent neoplastic disease in cattle. Due to the lack of commercially available vaccines, reliable eradication of the disease can be achieved through the testing and elimination of BLV antibody-positive animals. In this study, we developed a novel competitive ELISA (cELISA) to detect antibodies against BLV capsid protein p24. Recombinant p24 protein expressed by Escherichia coli, in combination with the monoclonal antibody 2G11 exhibiting exceptional performance, was used for the establishment of the cELISA. Receiver-operating characteristic curve analysis showed that the sensitivity and specificity of the assay were 98.85 % and 98.13 %, respectively. Furthermore, the established cELISA was specific for detecting BLV-specific antibodies, without cross-reactivity to antisera for six other bovine viruses. Significantly, experimental infection of cattle and sheep with BLV revealed that the cELISA accurately monitors seroconversion. In a performance evaluation, the established cELISA displayed a high agreement with Western blotting and the commercial BLV gp51 cELISA kit in the detection of 242 clinical samples, respectively. In conclusion, the novel p24 cELISA exhibited the potential to be a reliable and efficient diagnostic tool for BLV serological detection with a broad application prospect.

Critical regions and residues for self-interaction of grapevine leafroll-associated virus 2 protein p24

The 24-kDa protein (p24) encoded by grapevine leafroll-associated virus 2 (GLRaV-2) is an RNA-silencing suppressor. In this work, a yeast two-hybrid system (YTHS) and bimolecular fluorescence complementation analyses showed that GLRaV-2 p24 can interact with itself, and that this interaction occurs in the cytoplasm of Nicotiana benthamiana cells. To identify the functional region(s) and crucial amino acid residues required for p24 self-interaction, various truncated and substitution mutants were generated. YTHS assay showed that in both homologous pairing and pairing with the wild-type p24, the functional regions mapped to aa 10-180 or 1-170 which contain, respectively, all seven α-helices or the first six α-helices and the N-terminal end (aa 1-9) of the protein. When only the full-length p24 was an interaction partner, the functional region of aa 1-170 could be further mapped to aa 1-140 which contains four α-helices plus most of the fifth α-helix. Further analysis with substitution mutants demonstrated that hydrophobic residues I35/F38/V85/V89/W149 and V162/L169/L170, which may, respectively, mediate the inter-domain interaction of the same p24 monomer and the tail-to-tail association between two p24 counterparts, are crucial for homotypic p24-p24 interaction. In addition, substitution of two basic residues-R2 or R86-of p24, which may play important functional roles in RNA binding, did not seem to affect self-interaction of the mutants in yeast but had obvious effects in plant cells. Taken together, our results demonstrate the functional regions and crucial amino acids for p24 self-interaction.

p24 family proteins: key players in the regulation of trafficking along the secretory pathway

p24 family proteins have been known for a long time, but their functions have remained elusive. However, they are emerging as essential regulators of protein trafficking along the secretory pathway, influencing the composition, structure, and function of different organelles in the pathway, especially the ER and the Golgi apparatus. In addition, they appear to modulate the transport of specific cargos, including GPI-anchored proteins, G-protein-coupled receptors, or K/HDEL ligands. As a consequence, they have been shown to play specific roles in signaling, development, insulin secretion, and the pathogenesis of Alzheimer's disease. The search of new putative ligands may open the way to discover new functions for this fascinating family of proteins.

Rat chondrocyte-associated antigen identified as sialylated transmembrane protein Tmp21 belonging to the p24 protein family

Rabbit serum produced after transplantation of isolated rat chondrocytes [sensitized rabbit serum (SRS)] demonstrated M r ~ 74- and ~23-kDa (western blot analysis) antigens in rat chondrocyte extracts. Only the latter remained after reduction in 2-mercaptoethanol. Protein sequence analysis of 23-kDa chondrocyte-associated antigen (CAA) revealed that it corresponds to transmembrane Tmp21 protein belonging to the p24 protein family. These proteins mainly participate in the traffic between the endoplasmic reticulum and Golgi complex and in some cells appear also in the membrane of secretory granules and plasmalemma. Tmp21 extracted from chondrocytes was sialylated and ceased to bind SRS after deglycosylation. A previous study from our laboratory indicated that expression of CAA, now identified as sialylated Tmp21, decreased in cultured chondrocytes concomitantly with the decline of collagen type II and aggrecan and the rise of collagen type I and versican expression. Since the sialylated form of Tmp21 (also known as emp24) was not described in other tissues and seems to be specific for chondrocytes, we assume that CAA may be considered a chondrocyte differentiation antigen.

Trafficking of the myrosinase-associated protein GLL23 requires NUC/MVP1/GOLD36/ERMO3 and the p24 protein CYB

Proteins detrimental to endoplasmic reticulum (ER) morphology need to be efficiently exported. Here, we identify two mechanisms that control trafficking of Arabidopsis thalianaGLL23, a 43 kDa GDSL-like lipase implicated in glucosinolate metabolism through its association with the β-glucosidase myrosinase. Using immunofluorescence, we identified two mutants that showed aberrant accumulation of GLL23: large perinuclear ER aggregates in the nuclear cage (nuc) mutant; and small compartments contiguous with the peripheral ER in the cytoplasmic bodies (cyb) mutant. Live imaging of fluorescently tagged GLL23 confirmed its presence in the nuc and cyb compartments, but lack of fluorescent signals in the wild-type plants suggested that GLL23 is normally post-translationally modified for ER export. NUC encodes the MVP1/GOLD36/ERMO3 myrosinase-associated protein, previously shown to have vacuolar distribution. CYB is an ER and Golgi-localized p24 type I membrane protein component of coat protein complex (COP) vesicles, animal and yeast homologues of which are known to be involved in selective cargo sorting for ER-Golgi export. Without NUC, GLL23 accumulates in the ER this situation suggests that NUC is in fact active in the ER. Without CYB, both GLL23 and NUC were found to accumulate in cyb compartments, consistent with a role for NUC in GLL23 processing and indicated that GLL23 is the likely sorting target of the CYB p24 protein.