1. Phenylketonuria (PKU) TAM NGUYEN CHEM 4700

2. Introduction  PKU is a common inborn metabolic disorder caused by a deficiency of the liver enzyme phenylalanine hydroxylase.  It prevents normal metabolization of phenylalanine (Phe), one of the essential amino acids that cannot be manufactured by the body and must therefore be consumed in protein rich foods.  Untreated individuals may give off a musty odor and they excrete large amounts of phenylalanine in their urine.

3. Cause  The most common cause of PKU is a mutation in the gene coding for the enzyme phenylalanine hydroxylase (PAH).  The mutation causes a deficiency in the activity of this enzyme and leads to aberrant amino acid metabolism.  Localized misfolding occurs, in which the misfolding spreads until the entire four-subunit enzyme can no longer function  The buildup of phenylalanine hinders the development of the brain and causes mental retardation

4. Symptoms  Severe intellectual and developmental disabilities  Behavioral or social problems  Stunted or slow growth  A musty odor in urine, breath, or skin that is a result of the extra phenylalanine in the body  Fair skin and blue eyes, due to the body’s failure to transform phenylalanine into melanin (the pigment responsible for a person’s coloring).

5. Structure The structure of PAH. (A) The modeled structure of full-length tetrameric PAH (composite model prepared by combining the structures of tetrameric human PAH (residues 118-452; PDB 2PAH) and dimeric rat PAH (residues 19-427; PDB 2PHM)). (B) Detailed structure of PAH including thienylalanine and BH4 (PDB 1KW0).

6. Biochemical Nature  Phenylalanine hydroxylase in complex with cofactor tetrahydrobiopterin (BH4)  The structure of PAH is shown along with its interaction points to the cofactor bound to the active site proving an ideal basis for structure- based drug design.

7. Phenylalanine to Tyrosine  Enzymes are structures that allow amino acids to combine by acting on a substrate and producing a new product.  Individuals with PKU have a deficiency in the enzyme phenylalanine hydroxylase, which converts phenylalanine to tyrosine.  The enzyme catalyzes the hydroxylation of phenylalanine on the phenyl ring at the 4 position, to make tyrosine.

8. Metabolic Pathways  Individuals with PKU, phenylalanine could not converted into tyrosine, phenylalanine accumulates and tyrosine is deficient.  Excessive phenylalanine can be metabolized into phenylketones through the minor route, a transaminase pathway with glutamate.  Metabolites include phenylacetate, phenylpyruvate, and phenethylamine.  Elevated levels of phenylalanine in the blood and detection of phenylketones in the urine is diagnostic.

9. Phenylalanine vs. Tyrosine The coiled-coil motif is visible in the center of each tetramer. The iron bound in the active sites are shown as red spheres

10. NMR Structure http://www.drugbank.ca/spectra/nmr_one_d/1177

11. Treatment  The only treatment available for PKU is a diet where phenylalanine levels are strictly limited.  Meat, fish, eggs, cheese, milk products, legumes, and bread are all foods that have high levels of phenylalanine.  Artificial protein substitutes are given which contain amino acids without phenylalanine  Permanent monitoring of blood phenylalanine levels.

12. Screening Test  Newborn screening allows early identification and early implementation of treatment.  Usually a few drops of blood are obtained by a small prick on the heel, placed on a card and then sent for measurement.  Blood tested for excess phenylalanine, in which blood was placed on agar plate with bacteria that need phenylalanine to grow.

13. References  Leandro, João, Nina Simonsen, Jaakko Saraste, Paula Leandro, and Torgeir Flatmark. "Phenylketonuria as a Protein Misfolding Disease: The Mutation PG46S in Phenylalanine Hydroxylase Promotes Self-association and Fibril Formation." Biochimica Et Biophysica Acta (BBA) - Molecular Basis of Disease (2010): 106-20. Print.  Fusetti, F. "Structure of Tetrameric Human Phenylalanine Hydroxylase and Its Implications for Phenylketonuria." Journal of Biological Chemistry (1998): 16962-6967. Print.  Underhaug, Jarl, Oscar Aubi, and Aurora Martinez. "Phenylalanine Hydroxylase Misfolding and Pharmacological Chaperones." Current Topics in Medicinal Chemistry (2013): 36-42. Print.  “What Are Common Symptoms of Phenylketonuria (PKU)?” Web. 16 Mar. 2015..  "Introduction to Phenyketonuria." Faq. Web. 16 Mar. 2015..