- Macromolecular crystallography,
- Cryo-electron microscopy (cryo-EM)
- Multiangle light scattering,
- Small angle scattering,
- Ultra fast laser spectroscopy, and
- Dual Polarisation Interferometry and circular dichroism.
The term “protein” (from the Greek “pre-eminent” or “first”) was first used by the Swedish chemist Jöns Berzelius in 1838 for the complex organic nitrogen-rich substance found in the cells of all animals and plants. Over the following century these were found to be built from 20 different amino acids and to be linked together in linear polymers, known as polypeptide chains. For many years proteins were thought to be amorphous substances with variable compositions. Progress came with the separation of individual proteins from complex mixtures and the preparation of crystals of pure proteins, such as haemoglobin and the enzyme urease. In the late 1930s, Linus Pauling and Robert Corey in the United States used x-ray diffraction (a technique in which a beam of X-rays is passed through a crystal of the substance and the scattered rays measured) to determine the structures of amino acids and peptides. They also correctly predicted that many amino acid chains would fold into a stable conformation rather like a spiral staircase, now known as an - (alpha-) helix. Another milestone occurred in 1955 when the Cambridge scientist Fred Sanger chemically analysed insulin, a small protein hormone, and showed that it was built from a defined set of amino acids linked together in a unique linear sequence. Everyone now accepts that each kind of protein molecule has its own unique sequence of amino acids.
The Building Blocks of Protein:
There are nine essential (L-form) amino acids that your body requires and must be obtained from food (or supplementation), since the body cannot manufacture them from other amino acids. These are Histidine, Isoleucine, Leucine, Lysine, Methionin, Phenylalanine, Threonine, Tryptophan and Valine.
Non Essential Amino Acids
These are peptide-bonded amino acids from food sources such as whey, casein, milk and eggs. They may have hundreds or thousands of peptide bonded amino acids, and your body still needs to digest them and break them down into the singular amino acids that the body can utilize. Some of them never get absorbed. These predigested proteins will also have the good characteristics from food sources that may cause allergic reactions to food sensitive individuals.UPS Pharmaceutical grade, or the highest quality, pure, crystalline amino acids are the singular L-form amino acids. The body best utilizes these, since they do not require digestion and are easily absorbed. The best delivery system is capsules (not tablets), since heat and pressure, which are used in most tablets, can destroy amino acids. A protein molecule is made from a long chain of these amino acids, each linked to its neighbour through a covalent peptide bond. Proteins are therefore also known as polypeptides. Each type of protein has a unique sequence of amino acids, exactly the same from one molecule to the next. Many thousands of different proteins are known, each with its own particular amino acid sequence. The repeating sequence of atoms along the core of the polypeptide chain is referred to as the polypeptide backbone.
Beta-strands are an extended form in which the side chains alternate on either side of the extended chain. The backbones of beta-strands hydrogen bond with the backbone of an adjacent beta strand to form a beta-sheet structure. The strands in a beta sheet can be either parallel or anti-parallel and the hydrogen-bonding pattern is different between the two forms. Anti-parallel beta stands are often linked by short loops containing 3-5 residues in highly characteristic conformations. Longer loops are occasionally found where the loop plays an important role in substrate binding or an active site. The antigen-combining site of the immunoglobulin is an important example of this. Beta sheets can be internal to a protein (largely hydrophobic) or on the surface in which case they are amphipathic, with every other amino acid side chain alternating between hydrophobic and hydrophilic nature. The peptide backbone is constrained by steric hindrance, and hydrogen bonding patterns that limit its torsion angles (phi-psi angles) to certain limits. Plots of phi versus psi dihedral angles for amino acid residues are called Ramachandran plots.
- If extended strands are lined up side by side, H-bonds bridge from strand to strand. Identical or opposed strand alignments make up parallel or antiparallel beta sheets.
- Antiparallel beta-sheet is significantly more stable due to the well aligned H-bonds.