The Family Secrets of Avian Egg-Specific Ovalbumin and Its Related Proteins Y and X

Abstract

The ovalbumin gene family in Gallus gallus is composed of three homologous genes located within a 46 kb locus on chromosome 2: ovalbumin, ovalbumin-related protein Y (OVAY), and ovalbumin-related protein X (OVAX) genes. The expression of these genes in hen oviduct is under estrogen control, but their relative hormonal responsiveness and subsequent protein concentration in egg, is distinctive. Interestingly, all three proteins lack the classical signal peptide for secretion. Ovalbumin, OVAX, and OVAY belong to the serine protease inhibitor (serpin) family whose members share a common tertiary structure. Ovalbumin and OVAX are one of the few members of this family that do not express any protease inhibition activity whereas OVAY has been predicted to be inhibitory, by comparison with the consensus sequence for inhibitory serpins. In contrast to ovalbumin and OVAY, OVAX interacts with heparin, a negatively charged glycosaminoglycan, via a positively charged domain exposed at the surface of the molecule. Ovalbumin is the major egg white protein and might be a source of amino acids for the developing embryo. The physiological function of OVAY is not known, but recent data have revealed a possible role of this protein in early embryonic development. Considering the antibacterial activities of OVAX, this protein might play a role in egg defense. This review sheds light on the expression, biochemistry, and structural specificities of these three highly similar paralogs. It gives new clues in favor of diverging functions, which are likely to have arisen by duplication events from a common ancestral gene.

Emerging Evidence for the Importance of Dietary Protein Source on Glucoregulatory Markers and Type 2 Diabetes: Different Effects of Dairy, Meat, Fish, Egg, and Plant Protein Foods

“…Furthermore, the protein content and composition within different muscles of the same animal will also vary (e.g., light meat compared to dark meat in a chicken), as will the different proteins within any particular muscle (e.g., myofibrillar proteins are considered high quality complete proteins, while the stromal proteins in muscle are considered a low quality incomplete proteins [41] (Table 1). Eggs also contain structural proteins, along with hundreds of other functional proteins that have evolved to assist with various physiological processes revolving around embryonic nourishment and development [42]. The specific protein fractions are very different between the egg yolk and white [20] (Table 1).…”

Deleterious amino acid substitutions with a series of putative damaging effects on egg components are revealed in the ovalbumin gene family; an in silico approach

“…Whatever the pattern each nsSNP takes in the interruption of the ovalbumin family, the current finding indicated that these nsSNPs seriously affect the structure, function, and stability of ovalbumin family, which have a series of deleterious consequences on the biological pathways in which these proteins involved, such as egg defense activity, embryonic fertilization and development (Liu et al 2015;Akazawa et al 2019). Accordingly, its noteworthy to distinguish that both H365P and I167T, being the most deleterious nsSNPs in OVALX and OVALY, respectively, should take priority in terms of reducing antimicrobial activity in case of OVALX (Guyot et al 2016), or damaging embryonic development in case of OVALY (Da Silva et al 2015). This observation is particularly interesting, knowing that once these amino acid substitutions detected in a particular breed, serious precautions should be taken for breeders with respect to the handling of this breed.…”

“…All these three genes are mainly expressed in the oviduct (Sugimoto et al 2001), and more specifically by tubular gland cells of the chicken's magnum (Rehault-Godbert et al 2013). Sequences alignment of these three genes have shown a sequence identity of 73 % between OVAL and OVALX, of 72 % between OVAL and OVALY, and 82 % between OVALX and OVALY genes (Da Silva et al 2015). Although OVAL, OVALY, and OVALX proteins have exerted high homology in their primary sequences, distinct and subtle physicochemical and structural differences have exhibited among them that might be associated with specific function on each one.…”

“…OVALX gene and its closest neighbour OVALY gene, are highly similar genes and have a close relation with OVAL. Both have likely arisen by duplication events from a common ancestral OVAL gene because the two gene-coding sequences share highly significant similarity with that of the OVAL (Da Silva et al 2015). Though OVALX and OVALY properties have been described recently, their biological functions remain to be undefined.…”

Dynamics of Structural Barriers and Innate Immune Components during Incubation of the Avian Egg: Critical Interplay between Autonomous Embryonic Development and Maternal Anticipation

“…More than 300 proteins have been identified in the EW, 8 of which account for approximately 90% of the protein content: OVAL (54%), TF (12%), ovomucoid (SPINK7, 11%), ovoglobulin G 2 (BPIFB2/G2/TENP, 4%), ovomucin (3.5%), LYZ (3.4%), ovoinhibitor (SPINK5, 1.5%), and ovoglycoprotein (ORM1, 1%) [55, 57-62]. OVAL likely serves as a nutritional source of amino acids for the embryo [63]. OvoDA1/gallin, AvBD11, TF, LYZ, ovomucin, SPINK5, and SPINK7 participate in the antimicrobial activity of EW [64-67].…”