Unique progastrin processing in equine G-cells suggests marginal tyrosyl sulfotransferase activity.

This research investigates the unique processing of progastrin, a hormone precursor, in the G-cells of horses, suggesting a minimal activity of the enzyme tyrosyl sulfotransferase. The researchers cloned a progastrin gene and found notable differences compared to other species, with the equine gastrin having a substitution of an amino acid in a key region and less sulphation. Further studies showed that this reduced sulphation wasn’t due to the structure of gastrin, but a characteristic of the horse’s antral G-cells.

Research Methodology

• The researchers conducted a comparative study to understand the differences in progastrin processing between horses and other mammal species. They discovered a high degree of conservation in terms of gastrin, the hormone produced from progastrin, but found a significant substitution of an amino acid (Lysine for Glutamate) in a region which was previously assumed to be unchangeable across species.

Progastrin Sulphation Findings

• In other mammals, gastrin is significantly Tyrosine-sulphated, a process which helps increase its biological functionality. However, in horses, antral gastrins (gastrins produced in the upper part of the stomach) were found to be nearly unsulphated.
• The team transfected the equine preprogastrin cDNA into an endocrine cell line, leading to the production of highly sulphated gastrins. This showed that the lack of in situ (on-site) sulphation in horse gastrins is not due to the structure of the hormone, contradicting the initial assumption.

Evidence of Unique Tyrosyl Sulfotransferase Activity

• The results suggest that the horse’s antral G-cells, which produce gastrin, have unique tyrosyl sulfotransferase activity. Tyrosyl sulfotransferase is the enzyme that facilitates the sulphation process.
• This identified minimal activity of tyrosyl sulfotransferase in equine G-cells explains the high proportion of a type of gastrin, known as gastrin-34, compared to another type, known as gastrin-17, in the horse’s antrum (part of the stomach). This suggests that tyrosyl sulphation promotes the endoproteolytic processing of prohormones, in which large precursor molecules are cut into smaller, active hormones.