Egg lysin is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

that creates a hole in the envelope 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 a ...

thereby allowing the

sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...

to pass through the envelope and fuse with the egg.

Fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...

proteins are

acrosomal The acrosome is an organelle that develops over the anterior (front) half of the head in the spermatozoa (sperm cells) of many animals including humans. It is a cap-like structure derived from the Golgi apparatus. In placental mammals the acrosome c ...

proteins involved in various roles during the fertilization process. Structurally these proteins consist of a closed bundle of helices with a right-hand twist. Lysin and SP18, both characterised in

abalone Abalone ( or ; via Spanish , from Rumsen ''aulón'') is a common name for any of a group of small to very large marine gastropod molluscs in the family (biology), family Haliotidae. Other common name In biology, a common name of a taxon o ...

, are two evolutionarily related fertilization proteins that have distinctive roles. Following its release from sperm, lysin binds to the egg

vitelline Vitelline may refer to: Embryology * Vitelline arteries, arteries that bring blood to the yolk sac * Vitelline circulation, the system of blood flowing between an embryo and its yolk sac * Vitelline cyst, a developmental defect relating to the c ...

envelope (VE) via the VE receptor for lysin (VERL), then non-enzymatically dissolves the VE to create a hole, thereby allowing the sperm to pass through the envelope and fuse with the egg. Lysins exhibit species-specific binding to their egg receptor, possibly through differences in charged surface residues. SP18 is also released from sperm, acting as a potent fusagen of liposomes to mediate the fusion between the sperm and egg cell membranes. Despite a similarity in the overall fold, the variation in the surface features of SP18 and lysin account for their different roles in fertilization. The molecular basis of VERL-lysin interaction was revealed in June 2017 by researchers at

Karolinska Institutet The Karolinska Institute (KI; sv, Karolinska Institutet; sometimes known as the (Royal) Caroline Institute in English) is a research-led medical university in Solna within the Stockholm urban area of Sweden. The Karolinska Institute is consist ...

and

ESRF The European Synchrotron Radiation Facility (ESRF) is a joint research facility situated in Grenoble, France, supported by 22 countries (13 member countries: France, Germany, Italy, the UK, Spain, Switzerland, Belgium, the Netherlands, Denmark, ...

, who reported X-ray crystallographic and biochemical studies of both species-specific and non-species-specific complexes between the two proteins. The corresponding 3D structures ( and ), which suggest a mechanism for

vitelline envelope The insect vitelline envelope is the outer proteinaceous layer outside the oocyte and egg. The vitelline envelope, not being a cellular structure, is commonly referred to as a membrane. However, this is a technical misnomer as the structure is com ...

dissolution by lysin, visualized for the first time how sperm interacts with the egg coat at the atomic level.

References

{{DEFAULTSORT:Egg Lysin Protein domains Membrane proteins