About CRISP / Cysteine-Rich Secretory Protein:
Cysteine-rich secretory proteins are also often referred to as “CRISPs”. They are a group of glycoproteins that are a subgroup of the CRISP, antigen 5 and Pr-1 (CAP) protein superfamily. All cysteine-rich secretory proteins contain a domain related to the ShK toxins.
CRISP Structure
These proteins are glycoproteins. They have a number of carbohydrates glycans covalently attached to amino acid side-chains on their surface via glycosylation. In regards to structure, cysteine-rich secretory proteins contain two domains which are joined by a hinge region. The larger of these two domains is a CAP-like 'Pathogenesis-related 1' domain. This is commonly referred to as “PR-1”. The smaller region is an ShK-like 'Cysteine-Rich Domain'. This is also referred to as a “CRD”. The primary structure is also rich in cysteine that form disulfide bonds, particularly in the hinge region and CRD.
Cysteine-Rich Secretory Protein Function
Cysteine-rich secretory proteins play a major role in the functioning of the mammalian reproductive system. They are also found in a number of different snake venoms. Within these venoms, they can be found to inhibit both smooth muscle contraction and cyclic nucleotide-gated ion channels.
When it comes to mammalian reproduction, cysteine-rich secretory proteins can be found in the testes and epididymis of mammals. They are also involved in the process of fertilisation and the spermatogenesis process - this is the development of the spermatozoa in the testis. Here, the CRISP2 protein is incorporated into the acrosome where it is believed to be involved in the adhesion of germ cells with Sertoli cells. CRISP2 can also form part of the sperm tail. In the sperm tail, CRISP2 is believed to help regulate flagellar beating. Proteins CRISP1 and CRISP4 can also be found in the epididymis, where they are also incorporated within the spermatozoa as it matures. Then, protein CRISP3 is found in seminal fluid. It is excreted from the prostate. CRISP3’s function is unknown.