Structural organization of the genes for rat von Ebner's gland proteins 1 and 2 reveals their close relationship to lipocalins

Abstract

The rat von Ebner's gland protein 1 (VEGP 1) is a secretory protein, which is abundantly expressed in the small acinar von Ebner's salivary glands of the tongue. Based on the primary structure of this protein we have previously suggested that it is a member of the lipocalin superfamily of lipophilic-ligand carrier proteins. Although the physiological role of VEGP 1 is not clear, it might be involved in sensory or protective functions in the taste epithelium.Here, we report the purification of VEGP 1 and of a closely related secretory polypeptide, VEGP 2, the isolation of a cDNA clone encoding VEGP 2, and the isolation and structural characterization of the genes for both proteins. Protein purification by gel-filtration and anion-exchange chromatography using Mono Q revealed the presence of two different immunoreactive VEGP species. Nterminal sequence determination of peptide fragments isolated after protease Asp-N digestion allowed the identification of a new VEGP, named VEGP 2, in addition to the previously characterized VEGP 1. The complete VEGP 2 sequence was deduced from a cDNA clone isolated from a von Ebner's gland cDNA library. The VEGP 2 cDNA encodes a protein of 177 amino acids and is 94% identical to VEGP 1.DNA sequence analysis of the rat VEGP 1 and 2 genes isolated from rat genomic libraries revealed that both span about 4.5 kb and contain seven exons. The VEGP 1 and 2 genes are nonallelic distinct genes in the rat genome and probably arose by gene duplication. The high degree of nucleotide sequence identity in introns A-C (94-100%) points to a recent gene conversion event that included the 5' part of the genes.The genomic organization of the rat VEGP genes closely resembles that found in other lipocalins such as P-lactoglobulin, mouse urinary proteins (MUPs) and prostaglandin D synthase, and therefore provides clear evidence that VEGPs belong to this superfamily of proteins.The rat von Ebner's gland protein (VEGP) is highly expressed in small acinar salivary glands as shown by in situ hybridization (Schmale et al., 1990) and by immunohistochemistry (Kock et al., 1992). This protein is found in von Ebner's gland saliva, which drains into the clefts of the vallate and foliate papillae, where about 80% of the total number of taste buds of the rat tongue are located. Besides the close anatomical connection between von Ebner 's glands and taste buds, there is also a temporal correlation between VEGP expression and taste bud development (Kock et al., 1992). The saliva of these glands contains about 150 different proteins (Beidler, 1990) and most of these are not function-

Purification, cloning and characterisation of odorant- and pheromone-binding proteins from pig nasal epithelium

“…Differences among protein isoforms were limited to a few bases and corresponded to specific amino acid substitutions (Pro141 AE Leu in OBP-IIs; Val45 AE Ala, Ile48 AE Val and Ala73 AE Val in OBP-IIIs). These data are in good agreement with the previous detection in rat of two distinct genes encoding non-allelic VEG, which probably arose by gene duplica- tion [45]. Similar observations have also been reported for porcine SALs [35].…”

Taste of Fat: A Sixth Taste Modality?

“…In rodents and humans, VEG also produce and secrete various proteins including the VEG protein (VEGP) (98,182) which belongs to the lipocalin superfamily (FIGURE 1B). This lipophilic ligand carrier protein is known to bind a remarkable array of small hydrophobic molecules, including LCFA, phospholipids, retinol, or bitter compounds.…”

Complement component C8γ is expressed in human fetal and adult kidney independent of C8α

“…Since it is known that within the lipocalins several members of one specific protein family could be encoded by different, but very closely related genes [18, 19], we cloned the entire kidney‐specific C8γ transcript to perform sequence analysis. Therefore, poly(A) + RNA from human kidney was reverse‐transcribed and used as a template for PCR with oligonucleotide primers derived from the 5′‐ and 3′‐non‐translated regions of the C8γ cDNA.…”