Sandbox Reserved 642

This Sandbox is Reserved from 30/08/2012, through 01/02/2013 for use in the course "Proteins and Molecular Mechanisms" taught by Robert B. Rose at the North Carolina State University, Raleigh, NC USA. This reservation includes Sandbox Reserved 636 through Sandbox Reserved 685.

To get started: Click the edit this page tab at the top. Save the page after each step, then edit it again. Click the 3D button (when editing, above the wikitext box) to insert Jmol. show the Scene authoring tools, create a molecular scene, and save it. Copy the green link into the page. Add a description of your scene. Use the buttons above the wikitext box for bold, italics, links, headlines, etc. More help: Help:Editing For more help, look at this link: http://proteopedia.org/w/Help:Getting_Started_in_Proteopedia Phenylalanine HydroxylasePhenylalanine Hydroxylase Phenylalanine Hydroxylase(PheOH), otherwise known as phenylalaine-4-monooxygenase, is an enzyme produced by the PAH gene found on the twelfth chromosome in the human genome, but it is also found in some bacteria. This enzyme functions as a catalyst in the conversion of the amino acids phenylalanine to tyrosine by adding a hydroxyl group (-OH) to the benzene ring of the amino acid. This is why this protein is therefore classified as a hydroxylase. In most organisms, this hydroxylation process is the first step in phenylalanine degradation. A faulty PAH gene can cause an increase in phenylalanine level in the plasma, resulting in the genetic disorder Phenylketonuria (PKU). StructureStructure spinqualitylabelsall models This is a model of the pheylalanine hydroxylase dimer as found in humans. The green ball in within each subunit represents the iron ion in the catalytic domains. Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image PheOH can exist as a dimer or tetramer with identical subunits. Each subunit is organized to have a regulatory, a catalytic and a tetramerization domain. The native form of human PheOH has an estimated secondary structure composed 48% alpha-helices, 28% extended structures, 12% beta-turns, and 12% non-structured conformations. The more structured elements are usually concentrated in the catalytic C-terminal domain of the protein, while the more flexible and unstructured elements are grouped in the regulatory N-terminal domain. The PheOH model protein was generated via x-ray crystallography. Catalytic Domain The of phenylalanine hydroxylase includes resides 143-410. This region has a basket-like arrangement consisting of 13 alpha-helices and 8 beta-strands. This region of the protein also includes the active site. The active site of PheOH can be found in the center of the catalytic domain and is characterized by a 13 Angstroms deep and 10 Angstroms wide hydrophobic pocket. Lining the active site are 3 glutamates, 2 histadines and 1 tyrosine residue along with hydrophobic residues for a total of 34 amino acids. Covering the entrance of the active site is a short loop consisting or residues 378-381. The center of each catalytic domain consists of an iron ion which is vital to the enzyme activity. The iron atom binds in the active site to . Histadine 285 and 290 were found to be required for the binding of iron through site directed mutagenisis studies. The iron ions are coordinated to three water molecules and arrange in an octahedral geometry. The active site also binds the cofactor tetrahydrobiopterin. This cofactor binds closely to the iron ion and forma hydrogen bonds with two of the three water molecules. The cofactor also forms hydrogen bonds with the carbonyl oxygen of the protein residues including Ala322, Gly247, and Leu249 and the amide of Leu249. Tetramerization Domain spinqualitylabelsall models catalytic domain of human phenylalanine hydroxylase in its catalytically active Fe(II) form and binary complex with tetrahydrobiopterin Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image Phenylalanine Hydroxylase exists in equilibrium between a homodimer and a homotetramer. The region responsible for the tertamerization is the located at the C terminal end of the protein. It consists of residues 411-452. The tetramerization domain consists of 2 beta-strands forming a beta-ribbon and an alpha-helix that is 40 angstroms long. The four alpha helices, consisting of one from each monomer, pack into a coil coil motif with the helices arranged in an anti parallel manner.. The PheOH model protein was generated via x-ray crystallography. MechanismMechanism Although the exact mechanism of phenylalanine degradation is still not fully understood, the main reaction requires the addition of an hydroxyl group to the benzene ring of the phenylalanine residue. In order for this process to occur, the cofactor tetrahydrobiopterin(BH4) loses two hydrogen atoms to become dihydrobiopterin. BH4 acts as a reductant by reducing one of the diatomic oxygens while the other is added to the 6-membered ring. In order to stabilize the substrate- enzyme complex as this reaction occurs, an iron atom within the protein is necessary. It is within the active site that the hydrogen atom from phenylalanine is stripped off and replaced with a hydroxyl group. Reaction catalyzed by PheOH Implications or Possible ApplicationsImplications or Possible Applications The first diagnosed cases of Phenylketonuria (PKU), otherwise known as Folling's Disease, were identified in 1934 by Norwegian doctor and biochemist Asbjorn Folling. Dr. Folling found that the urine of two of his young mentally handicapped patients contained a high level of phenylalanine. Follwing this discovery, it was found that the absence or malfunction of the phenylalanine hydroxylase enzyme is due to the mutation of the PAH gene and inherited autosomal recessively. This may result in a genetic disorder known as Phenylketonuria (PKU). This information was not utilized until the early 1950s when it was found that under a low phenylalanine diet, some of the symptoms found in children suffering from PKU could be reversed. Due to a diet rich in phenylalanine, this enzyme is vital in the regulation in phenylalanine plasma concentration by converting about 75% of the amino acid to tyrosine. Excessive amounts of phenylalanine has been shown to cause mental retardation in humans. Presently, it is regulation to screen newborns children for phenylketonuria with a simple blood or urine test. Due to his discovery and development of the PKU test, Dr. Folling is remembered as one of the most important medical scientists that has not received a Nobel Prize for Physiology or Medicine. SymptomsSymptoms PKU diet Phenylalanine plays a variety of roles in the body among which is the production of melanin, the pigment responsible for hair and and skin color. Infants with an over abundance of this residue may therefore have a lighter skin, hair and eye color than those who do not. Other symptoms may include: - Delayed mental and social skills - Head size significantly below normal - Hyperactivity - Jerking movements of the arms or legs - Mental retardation - Seizures - Skin rashes - Tremors - Unusual positioning of hands TreatmentTreatment Treatment for such a PKU is a low phenylalanine diet and early detection. Those who start the diet early and adhere to it will have better mental and physical health. Infants diagnosed with the disease can fed a specially made formula called Lofenalac while others should follow a diet plan as illustrated in the image to the left. The main rule to follow is to avoid protein sources rich in phenylalanine and sugars containing aspartame. Taking extra supplements like fish oil can replace the fatty acids missing from the phenylalanine free diet and may also improve neurological development. PKU can also be caused by a deficiency in or inability to regenerate tetrahydrobipternin, the cofactor essential to the function of PheOH. Although this is not usually the cause of PKU, patients can be treated by taking tetrahydrobiopterin supplements. If the diet is not strictly followed, mental retardation may result after the first year of life. ReferencesReferences