Phosvitin is one of the

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the ...

(commonly hen's egg)

yolk Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example bec ...

phosphoprotein A phosphoprotein is a protein that is posttranslationally modified by the attachment of either a single phosphate group, or a complex molecule such as 5'-phospho-DNA, through a phosphate group. The target amino acid is most often serine, threonin ...

s known for being the most

phosphorylated In biochemistry, phosphorylation is described as the "transfer of a phosphate group" from a donor to an acceptor. A common phosphorylating agent (phosphate donor) is ATP and a common family of acceptor are alcohols: : This equation can be writt ...

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

found in nature. Phosvitin isolation was first described by Mecham and Olcott in the year 1949. Recently it has been shown that phosvitin orchestrates nucleation and growth of biomimetic bone like apatite.

Structure

As the most phosphorylated natural protein, phosvitin contains 123 phosphoserine residues accounting for 56.7% of its total 217

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

residues. The structure of phosvitin at large consists of 4-12 base pair stretches of serines, interspersed with amino acid residues

lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. Lysine contains an α-amino group (which is in the protonated form when the lysine is dissolved in water at physiological pH), an α-carboxylic acid group ( ...

(6.9%),

histidine Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an Amine, α-amino group (which is in the protonated –NH3+ form under Physiological condition, biological conditions), a carboxylic ...

(6.0%), and

arginine Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidinium, guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) a ...

(5.1%), among others in smaller quantities. Phosvitin’s structure (right) is adapted from the protein

vitellogenin Vitellogenin (VTG or less popularly known as VG) (from Latin ''vitellus'', yolk, and ''genero'', I produce) is a precursor of the egg yolk proteins. It is synthesized and secreted by the liver of vertebrates, fat body of insects and the hepatopa ...

(Gene: VTG2; Uniprot: P02845; residues 1-1850) generated by

AlphaFold AlphaFold is an artificial intelligence (AI) program developed by DeepMind, a subsidiary of Alphabet, which performs predictions of protein structure. It is designed using deep learning techniques. AlphaFold 1 (2018) placed first in the overall ...

, where all the possible phosphorylated serine residues are highlighted in red. Phosvitin is one of four proteins cleaved from vitellogenin and is unstructured at neutral pH. Despite phosvitin only accounting for 16% of total proteins in egg

, it alone accounts for 60% of the total yolk

phosphoproteins A phosphoprotein is a protein that is posttranslationally modified by the attachment of either a single phosphate group, or a complex molecule such as 5'-phospho-DNA, through a phosphate group. The target amino acid is most often serine, threonin ...

as well as 90% of the total yolk phosphorus.

Function

Due to phosvitin’s polyanionic activity, the protein performs functionalities such as metal

chelation Chelation () is a type of bonding of ions and their molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These l ...

, emulsification, and nutrition sequestration for a growing

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

. Additionally, in recent research it has been shown that the disordered

secondary structure Protein secondary structure is the local spatial conformation of the polypeptide backbone excluding the side chains. The two most common Protein structure#Secondary structure, secondary structural elements are alpha helix, alpha helices and beta ...

of phosvitin orchestrates

nucleation In thermodynamics, nucleation is the first step in the formation of either a new Phase (matter), thermodynamic phase or Crystal structure, structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically def ...

and growth of biomimetic bone like apatite.

Structure

Function

References

Further reading