Abstract
Tetrahydrobiopterin (BH4) is an essential cofactor for many vital enzymes. It was initially identified as a cofactor for aromatic amino acid hydroxylases, and later was also found to be an essential cofactor for all isoforms of nitric oxide synthase. Nitric oxide (NO) is an important signalling molecule that plays critical roles in the regulation of the cardiovascular, neuronal and immune systems. In the cardiovascular system NO acts as a potent vasodilator and is needed to maintain healthy endothelial function, vascular tone and hence blood pressure. BH4 is therefore essential for normal NO production. Administering high intravenous concentrations of BH4 to patients with diseases associated with endothelial dysfunction (diabetes, hypertension and hypercholesterolaemia), elicits an improvement in endothelial function which is likely to result from a rise in NO bioavailability. Genetically modified animals with reduced BH4 bioavailability display pulmonary hypertension whereas animals with increased BH4 bioavailability are protected, in a number of cardiovascular disease models.
GTP cyclohydrolase 1 (GCH1) is the enzyme involved in the committing and rate limiting step of BH4 biosynthesis. In vitro, the activity of GCH1 is regulated allosterically through protein–protein interactions with GTP cyclohydrolase 1 feedback regulatory protein (GFRP). In vitro, GCH1 activity has been shown to be modified by levels of phenylalanine and BH4 through alterations in the allosteric interaction between GCH1 and GFRP. Published X-ray crystallography and in vitro studies have shown that phenylalanine binds to and activates the GCH1–GFRP complex, whilst increased BH4 has the opposite effect. The importance of this physical protein–protein interaction on BH4 bioavailability in vivo has yet to be fully understood, although it is known that a phenylalanine challenge in humans results in a rise in plasma biopterin (a stable end product of BH4 oxidation).
The significance of the GCH1–GFRP interaction is currently being investigated in our lab. Preliminary studies carried out on mice and rats following phenylalanine administration have shown that circulating biopterin levels are increased.
In order to investigate the protein–protein interactions between GCH1 and GFRP further, human GCH1 and GFRP will be recombinantly expressed and using biophysical techniques we will study how these proteins interact and affect functionality. By understanding the basics of how GCH1–GFRP interact and how it translates to BH4 levels we can pave way to further developing a novel therapeutic target against a range of common disease states.
GTP cyclohydrolase 1 (GCH1) is the enzyme involved in the committing and rate limiting step of BH4 biosynthesis. In vitro, the activity of GCH1 is regulated allosterically through protein–protein interactions with GTP cyclohydrolase 1 feedback regulatory protein (GFRP). In vitro, GCH1 activity has been shown to be modified by levels of phenylalanine and BH4 through alterations in the allosteric interaction between GCH1 and GFRP. Published X-ray crystallography and in vitro studies have shown that phenylalanine binds to and activates the GCH1–GFRP complex, whilst increased BH4 has the opposite effect. The importance of this physical protein–protein interaction on BH4 bioavailability in vivo has yet to be fully understood, although it is known that a phenylalanine challenge in humans results in a rise in plasma biopterin (a stable end product of BH4 oxidation).
The significance of the GCH1–GFRP interaction is currently being investigated in our lab. Preliminary studies carried out on mice and rats following phenylalanine administration have shown that circulating biopterin levels are increased.
In order to investigate the protein–protein interactions between GCH1 and GFRP further, human GCH1 and GFRP will be recombinantly expressed and using biophysical techniques we will study how these proteins interact and affect functionality. By understanding the basics of how GCH1–GFRP interact and how it translates to BH4 levels we can pave way to further developing a novel therapeutic target against a range of common disease states.
| Original language | English |
|---|---|
| Pages (from-to) | 353-353 |
| Number of pages | 1 |
| Journal | VASCULAR PHARMACOLOGY |
| Volume | 56 |
| Issue number | 5-6 |
| DOIs | |
| Publication status | Published - 2012 |