Protein structure

Abstract: A computer program that progressively evaluates the hydrophilicity and hydrophobicity of a protein along its amino acid sequence has been devised. For this purpose, a hydropathy scale has been composed wherein the hydrophilic and hydrophobic properties of each of the 20 amino acid side-chains is taken into consideration. The scale is based on an amalgam of experimental observations derived from the literature. The program uses a moving-segment approach that continuously determines the average hydropathy within a segment of predetermined length as it advances through the sequence. The consecutive scores are plotted from the amino to the carboxy terminus. At the same time, a midpoint line is printed that corresponds to the grand average of the hydropathy of the amino acid compositions found in most of the sequenced proteins. In the case of soluble, globular proteins there is a remarkable correspondence between the interior portions of their sequence and the regions appearing on the hydrophobic side of the midpoint line, as well as the exterior portions and the regions on the hydrophilic side. The correlation was demonstrated by comparisons between the plotted values and known structures determined by crystallography. In the case of membrane-bound proteins, the portions of their sequences that are located within the lipid bilayer are also clearly delineated by large uninterrupted areas on the hydrophobic side of the midpoint line. As such, the membrane-spanning segments of these proteins can be identified by this procedure. Although the method is not unique and embodies principles that have long been appreciated, its simplicity and its graphic nature make it a very useful tool for the evaluation of protein structures.

Abstract: Introduction and Survey. THE FOUNDATIONS: STRUCTURE AND NMR OF BIOPOLYMERS. NMR of Amino Acid Residues and Mononucleotides. NMR Spectra of Proteins and Nucleic Acids in Solution. The NMR Assignment Problem in Biopolymers. Two-Dimensional NMR With Proteins and Nucleic Acids. Nuclear Overhauser Enhancement (NOE) in Biopolymers. RESONANCE ASSIGNMENTS AND STRUCTURE DETERMINATION IN PROTEINS. NOE-Observable 1H-1H Distances in Proteins. Sequence-Specific Resonance Assignments in Proteins. Polypeptide Secondary Structures in Proteins by NMR. Three-Dimensional Protein Structures by NMR. RESONANCE ASSIGNMENTS AND STRUCTURE DETERMINATION IN NUCLEIC ACIDS. NOE-Observable 1H-1H Distances in Nucleic Acids. Resonance Assignments in Nucleic Acids Using Scalar Couplings. Nucleic Acid Conformation, 1H-1H Overhauser Effects, and Sequence-Specific Resonance Assignments. WITH NMR TO BIOPOLYMER CONFORMATION AND BEYOND. Conformation of Noncrystalline Proteins and Nucleic Acids. NMR Studies of Intermolecular Interactions with Biopolymers. References. Index.

Abstract: A program is described for drawing the van der Waal’s surface of a protein molecule. An extension of the program permits the accessibility of atoms, or groups of atoms, to solvent or solute molecules of specifiedsize to be quantitatively assessed. As defined in this study, the accessibility is proportional to surface area. The accessibility of all atoms in the twenty common amino acids in model tripeptides of the type Ala-X-Ala are given for defined conformation. The accessibilities are also given for all atoms in ribonuclease-S, lysozyme and myogobhn. Internal cavities are defined and discussed. Various summaries of these data are provided. Forty to fifty per cent of the surface area of each protein is occupied by non-polar atoms. The actual numerical results are sensitive to the values chosen for the van der Waal’s radii of the various groups. Since there is uncertainty over the correct values for these radii, the derived numbers should only be used as a qualitative guide at this stage. The average change in accessibility for the atoms of all three proteins in going from a hypothetical extended chain to the folded conformation of the native protein is about a factor of 3. This number applies to both polar (nitrogen and oxygen) and non-polar (carbon and sulfur) atoms considered separately. The larger non-polar amino acids tend to be more “buried” in the native form of all three proteins. However, for all classes and for residues within a given class the accessibility changes on folding tend to be highly variable.

Abstract: Two large-scale yeast two-hybrid screens were undertaken to identify protein-protein interactions between full-length open reading frames predicted from the Saccharomyces cerevisiae genome sequence. In one approach, we constructed a protein array of about 6,000 yeast transformants, with each transformant expressing one of the open reading frames as a fusion to an activation domain. This array was screened by a simple and automated procedure for 192 yeast proteins, with positive responses identified by their positions in the array. In a second approach, we pooled cells expressing one of about 6,000 activation domain fusions to generate a library. We used a high-throughput screening procedure to screen nearly all of the 6,000 predicted yeast proteins, expressed as Gal4 DNA-binding domain fusion proteins, against the library, and characterized positives by sequence analysis. These approaches resulted in the detection of 957 putative interactions involving 1,004 S. cerevisiae proteins. These data reveal interactions that place functionally unclassified proteins in a biological context, interactions between proteins involved in the same biological function, and interactions that link biological functions together into larger cellular processes. The results of these screens are shown here.

Abstract: Publisher Summary This chapter explores that the changes that take place in the protein molecules during denaturation constitute one of the most interesting and complex classes of reactions that can be found either in nature or in the laboratory These reactions are important because of the information they can provide about the more intimate details of protein structure and function They are also significant because they challenge the chemist with a difficult area for the application of chemical principles The chapter reviews that the denaturation is a process in which the spatial arrangement of the polypeptide chains within the molecule is changed from that typical of the native protein to a more disordered arrangement The chapter also discusses the classification of protein structures: primary, secondary, and tertiary structures The primary structure is that expressed by the structural chemical formula and depends entirely on the chemical valence bonds that the classical organic chemist would write down for the protein molecule The secondary structure is the configuration of the polypeptide chain that results from the satisfaction of the hydrogen bonding potential between the peptide N-H and C=O groups The tertiary structure is the pattern according to which the secondary structures are packed together within the native protein molecule The term “denaturation” as used in this chapter is indented to include changes in both the secondary and tertiary structures