; R o o t E n t r y F Ek 9 @ C o m p O b j b W o r d D o c u m e n t O b j e c t P o o l Ek 9 Ek 9 F Microsoft Word 6.0 Document MSWordDoc Word.Document.6 ; Oh +' 0 $ H l D h R:WWUSERTEMPLATENORMAL.DOT marcia steinberg marcia steinberg @ > 9 @ e = e j j j j j j j B L # $ T 4 B j B j j j j ~ j j j j 7 9506088 Bernlohr Just as there are carrier proteins that function to solubilize and deliver hydrophobic molecules in the circulatory system, there exists an analogous family of proteins that are found intracellularly. These proteins, which have been termed the lipid binding proteins, are responsible for the intracellular solubilization and delivery of hydrophobic ligands within a cell. The members of the lipid binding protein family are expressed in a more or less tissue specific manner, hence the naming of each member based upon the cell type it is expressed in. The lipid binding proteins bind most avidly to fatty acids and retinoids although some weak association with such molecules as heme and lysophospholipids does occ ur. Despite the wide variability in primary sequence, the three dimensional structure of the family members, as determined by multidimensional NMR and X ray crystallography, are remarkably superimposable. The unique feature of all the lipid binding proteins is the presence of an internal water filled cavity that serves as the ligand binding domain within a beta barrel folding motif. A l:l complex is formed between the proteins and the ligand within the cavity. Once inside, the ligand is sequestered from the external milieu and is held rigidly along one wall of the binding domain. Despite the finding of the ligand bound to the protein within the cavity, there is no obvious site for ligand entry/exit. A large water filled cavity that serves as the ligand binding domain seems intuitively contradictory to the purpose of the proteins. If the proteins facilitate the solubilization of water insoluble lipids why enclose them in a cavity filled with water? How do ligands enter and exit the cavity? What are the thermodynamic factors which govern protein structure and lipid binding? What determines the ligand binding specificity? The goals for this project are to understand in molecular terms the factors which contribute to ligand binding by the adipocyte lipid binding protein. A long term goal is to engineer the molecule to be of general use as a hydrophobic ligand carrier capable of high affinity association with a wide number of poorly soluble molecules such as environmental carcinogens and mutagens. To achieve these goals a more complete understanding of the basis for protein fatty acid interaction is needed. %%% Molecules that cannot dissolve readily in water pose special problems in biological systems. While water soluble biological molecules such as sugars and amino acids readily diffuse throughout aqueous space, water insoluble compounds in biological systems must be carried on proteins. The focus of these studies is on the most common type of hydrophobic ligand carrier proteins, the lipid bindin g proteins. In particular the P.I. studies in detail the adipocyte lipid binding protein. This protein is the prototype for over 50 different proteins, all of which facilitate the solubilization of hydrophobic compounds in biological systems. The adipocyte lipid binding protein associates with high affinity and selectivity with long chain fatty acids. The X pay crystal structure of the protein has been solved to high resolution and reveals the surprising finding that the hydrophobic, insoluble fatty acids are bound within a large central, water filled cavity. The binding of insoluble molecules into a water filled cavity is intuitively contradictory. By altering the amino acids in the binding domain and by measuring the properties of the protein lipid interactions, the P.I. is trying to understand the "rules" which govern the binding of such insoluble molecules. Once such rules are identified, new proteins might be engineered that are capable of binding hydrophobic compounds such as environmental pollutants and carcinogens that accumulate in the biosphere. *** @ @ ; S u m m a r y I n f o r m a t i o n (
