Primary structure of equine pituitary prolactin.

This research paper reveals that equine prolactin, a hormone secreted by the pituitary gland of horses, is a single-chain protein constituted of 199 amino acids. It also shows high similarity with porcine and fin whale prolactins. Interestingly, the study supports the theory that prolactins evolve faster than growth hormones.

Research Methods and Results

• The study used automated Edman analyses to identify the primary sequence of equine prolactin. This method helps in analyzing proteins by sequencing amino acids.
• Equine prolactin was found to be composed of a single chain of 199 amino acids. This included two tryptophan residue and six cysteine residues, similar to other mammalian prolactins.
• The researchers discovered that there were changes, presumably due to genetic mutations, in 17 out of the 199 residues that make up equine prolactin compared to its supposed ancestral precursor.
• Equine prolactin was also found to be closely similar to both porcine (pig) prolactin at 93% homology, and fin whale prolactin at somewhere between 87-91%.

Theory Supported and Implications of Findings

• The researchers observed that equine growth hormone, another hormone secreted by the pituitary gland, had only 4 changes in its residues in comparison to the same precursor protein. This suggests that prolactins, in general, are evolving at a faster rate than growth hormones.
• These findings have several implications for our understanding of how hormonal evolution works. The fairly substantial difference in the mutation rate between prolactin and the growth hormone suggests different levels of evolutionary pressure on these hormones.
• Understanding such evolutionary changes can aid in the development of treatments for conditions associated with hormonal imbalances since it could provide insight into how changes in hormonal structures can impact their function.
• The study also utilized circular dichroic spectrometry, which revealed that 60% of the equine prolactin protein has the potential to form alpha helices, which are common structure in proteins and play essential roles in protein’s functionality.