How Do Defective Proteins Lead to Diseases?Defective Proteins and Diseases:Slide 3Slide 4Slide 5Sickle cell anemia- A Defective TransporterSickle cell anemiaCF: Defective ChannelSlide 9Slide 10Slide 11Defective Receptor- FHSlide 13Transport of Lipids – Lipoproteins:Slide 15Slide 16MD : defective structural proteinThe ECM and Cytoskeleton Are Directly LinkedTreatments:Genetic EngineeringIntroductionHow Do Defective Proteins Lead to Diseases?Genetic mutations are often expressed as proteins that differ from wild-type.Genetic diseases can result from abnormalities in enzymes, channel proteins, receptor proteins, transport proteins, structural proteins, etc.Defective Proteins and Diseases:•PKU and Albinism : altered or defective enzyme•Sickle cell anemia: altered transport protein•CF: altered channel protein•FC: altered receptor•MD: altered structural proteinPhenylketonuria (PKU) was traced to its molecular phenotype in the 1950s.Results from an abnormal enzyme phenylalanine hydroxylase—normally catalyzes conversion of dietary phenylalanine to tyrosine.The abnormal enzyme has tryptophan instead of arginine in position 408.PKU – Defective Enzyme:•(1) Phenylketonuria (defective enzyme= phe hydroxylase•(2) Albinism (defective enzyme= tyrosinase) Phe || tyr || Fumarate +acetoacetate  (2)   acetyl CoA  Melanin aerobicPhenyl pyruvate oxidation Phenyl lactatePhenyl acetate(1)•People with PKU have light skin and hair color.•Melanin—pigment in dark skin and hair, is made from tyrosine, which people with PKU can not synthesize.•Nutra-sweet and PKU?Sickle cell anemia- A Defective TransporterThe first human disease known to be caused by an abnormal protein was sickle-cell disease.In sickle-cell disease, one of 146 amino acids in the β-globin chain is different: glutamic acid (negatively charged-hydrophilic) is replaced by valine (neutral-hydrophobic).Sickle cell anemia•A protein’s primary structure is its unique sequence of amino acids. •Because the amino acid R-groups affect a polypeptide’s properties and function, just a single amino acid change can radically alter protein function. •A missense mutation!abnormal hemoglobin  sickle-shaped blood cells.CF: Defective ChannelIn cystic fibrosis (CF), thick dry mucous lines surfaces such as the respiratory tract and prevents passage of air, and prevents cilia from functioning.This is caused by a nonfunctional chloride channel protein (Phe 508 of the transporter protein is missing in many patients. Codon for phe is missing [3 nucleotides missing ] reading frame is the same)Normally, this ion channel releases Cl– outside the cell. Water leaves cell by osmosis, providing moist surfaces.[Scientific American- Dec 1995]The transmembrane proteins that transport molecules are called transport proteins. There are three broad classes of transport proteins, each of which affects membrane permeability: 1. Channels2. Carrier proteins 3. PumpsCystic FibrosisTransmembrane Conductance Regulator:Is it a chloride channel?Defective Receptor- FHSome diseases result from altered or defective membrane receptors.Familial hypercholesterolemia (FH)—excess cholesterol can accumulate on artery walls and block them, causing heart attacks and strokes. People with FH are unable to internalize cholesterol to the liver cells and other cells that use it. Cholesterol travels as a lipoprotein (LDL). LDL binds to a receptor on a liver cell, and is taken up by endocytosis.In FH, the receptor protein is nonfunctional.What is a lipoprotein? Endocytosis?Lipid Transport: Lipoproteins – Lipids are transported in the blood stream by lipoproteins.Cholesterol, which is water insoluble, is synthesized in the liver and transported throughout the body within lipoprotein particles. (Lipids are packaged into lipoproteins  to bloodstream.)Transport of Lipids – Lipoproteins:•Cholesterol: mainly non polar; cannot dissolve in blood. (which is an aqueous medium).•An adult can synthesize about 800 mg cholesterol/day!!!•Primary form of cholesterol in blood  associated with lipoproteins, HDL ("good") and LDL ("bad")•Complexes of protein and lipid help together by non-covalent interactions. proteinHDL High Density LipoproteinLDL Low Density LipoproteinReceptor mediated endocytosis:Defective receptor (genetic disease)  high LDL in blood  heart attacks at age of 2 (homozygote)  die before 20 yrs.Receptor mediated endocytosis: highly specific. Depends on receptor proteins—integral membrane proteins—to bind to specific substancesGenetic Diseases of Membrane Receptor Proteins:Statin drugs used to treat familial hypercholesterolemia are examples of metabolic inhibitors. Statin blocks cholesterol synthesis.~ 80% cholesterol is converted to bile salts by the liver only way to excrete steroids. Use of “Resin”?MD : defective structural proteinDuchenne muscular dystrophy caused by altered structural proteins.In Duchenne muscular dystrophy (MD), there is no functional dystrophin, which normally connects actin fibers of muscle cells to the extracellular matrix. Without it, muscle cells are structurally disorganized, and stop working.______________________________________________Hemophilia is caused by the absence of a blood clotting protein (factor VIII). Normally, clotting factors (proteins) are always present in the blood.The ECM and Cytoskeleton Are Directly Linked•The ECM is strengthened by connections to transmembrane proteins.Direct linkage between the cytoskeleton and ECM keeps individual cells in place and helps adjacent cells adhere to each other  work togetherTreatments:1. Restricting substrates2. Metabolic inhibitors3. Supplying the missing proteinWhat if we can replace the defective gene with the normal?DNA has to be introduced in a way that ensures expression of the gene in the correct tissue, correct amount and at the correct time!Genetic Engineering•When an organism is intentionally altered at the molecular level to exhibit different traits, it has been genetically engineered•One focus of genetic engineering has been gene therapy, where cells of specific tissues in a living person are altered in a way that alleviates the affects of a disease  not straight forward•Another focus: The reproductive power of bacteria can be used to express large quantities of a mammalian protein of interest, however, process can be complicatedIntroduction