Crystal structure and reaction mechanism of LacY

Of the MFS-proteins currently only one example structure at molecular resolution (3.6 A) is available 1 , that of the E. coli lactose permease (LacY, see fig. 17.11). The molecule consists of two domains (helices 16 and 7-12), which are folding homologues although sequence homology is low. A mutant protein (C154G) was used for crystallisation, as this mutant is locked in the inward-facing conformation. This reduction in conformational freedom makes crystallisation possible, at the resolution of...

Enzyme kinetics special cases

In an enzyme following HMM-kinetics, enzyme activity rises gradually with substrate concentrations. For many physiological situations this is appropriate, the enzyme activity adapts to the metabolic needs of the cell. In this chapter we want to look at some cases, where such a gradual response would be inadequate, where instead a steep, switch-like, all-or-nothing response is required. Binding of a few hormone molecules to the receptors on the membrane of a cell can affect considerable changes...

Inherited diseases relating to haemoglobin

Sickle cell anaemia is an autosomal recessive disorder (i.e. the gene needs to be inherited from both parents for the disease to become manifest) which affects mostly Africans and their descendants. It is caused by a mutation in the gene for the ,3-subunit of haemoglobin (pS), leading to the substitution of Glu-6 with Val. The resulting haemoglobin is called HbS. The substitution of a charged amino acid by a hydrophobic one creates a hydrophobic patch, which is exposed in deoxy-haemoglobin, but...

Uncoating of clathrin coated vesicles

Because of their clathrin coats, clathrin coated vesicles can not fuse directly with the endosome. And because clathrin coats form spontaneously, energy is required to disassemble them again. This reaction is catalysed by a molecular chaperone, Hsc70 (see page 212), also known as the uncoating ATPase. There is an equilibrium between bound and free clathrin arms. Hsc70-ATP binds to exposed clathrin arms, preventing them from rejoining the coat. This shifts the equilibrium from coat assembly to...

A2 Short biographies of scientists mentioned in this book

Alper, Tikvah South Africa, 1909-1995. Born as fourth daughter of an immigrant from Russia she obtained a scholarship to study Physics at Capetown University, where she received her M.A. at the age of 20. She then moved to Germany, where she worked on the -rays from a-particles with L. Meitner but failed to obtain a PhD because growing antisemitism in Germany forced her to return to South Africa (she was awarded a D.Sc. by London University in 1969). She married the bacteriologist Max Stern in...

A brief history of enzymology

Most of the topics in this brief overview are covered in more detail in the following chapters. For further reading into enzymology 5, 18, 45 are suggested. If you have to deal with rate equations in special cases 70 is still useful. The properties of catalysts were described by the German-Russian chemist Gottlieb Sigismund Constantin Kirchhoff, who could show in 1812 that the hydrolysis of starch to glucose is accelerated by acid, and that the acid is not used up in the process1. In 1814 he...

Shuttles uniporters

Shuttles bind their substrates on one side of the membrane and release it on the other. The simplest shuttles are the so called uncouplers, lipophilic acids that dissolve in the membrane of mitochondria, bind protons on the acidic side and release them on the basic. Thus the proton gradient across the mitochondrial membrane is dissipated (the stored energy is converted into heat) and ATP production ceases. Figure 17.12. 2,4-Dinitrophenol is a typical uncoupler. The hydrophobic molecule can...

L

Immunoglobulin Nature

Antibodies consist of several copies of a characteristic motive, two anti-parallel -pleated sheets on top of each other and connected by a disulphide bond (see fig. 10.2). This Ig-fold is found in many proteins in the immune system and some other proteins with different function. There are some differences in the sequences even of the constant regions of antibodies between individuals. About 20 such allotypes have been identified in human heavy, a few more in the light chain. Some such...

Mechanism of movement

There are atypical flagella in some organisms with 3 0, 6 0 or 9 0 organisation, all of which are motile. At the very least this proves that the central pair of microtubules is not necessary for movement. Experimentally it is possible to remove the plasma membrane with detergent, the remaining structure is still motile, so the plasma membrane is not required for movement either. If such preparations are treated with proteases to remove the structural linkages between microtubules, bending is no...

Medical aspects

Correct triple helix formation see fig. 13.2 depends critically on the post-translational hydroxylation of proline to hydroxyproline by a hydroxylase in the ER-membrane. If this reaction is not carried out, triple helix dissociation temperature drops below 20 C, i.e. the helices are unstable at body temperature. Pro-hydroxylase contains a Fe2 -centre which can be oxidised to inactive Fe3 by a side reaction. Hy-Pro formation therefore requires the presence of Vitamin C ascorbic acid to reduce...

C5

Classical pathway of complement activation. Top The C1q,r,s complex can bind to immunoglobulins bound to antigen. At least 1 IgM or 2 IgG are required. Binding of the hexameric C1q protein to Ig results in C1r cleaving and activating C1s. Activated C1s can cleave C4 into C4a a weak inflammatory peptide and C4b, which binds to the membrane. This binding is covalent Cleavage of C4 exposes a reactive thioester bond between Glu and Cys in C4b, which reacts with OH-groups in proteins...

Cytogenetics

Colchicine from the autumn crocus Colchicium autumnale L., an alpine flower is used to treat acute gout, but can also arrest cells in metaphase by tubulin-depolymerisation. Metaphase-cells have their chromosomes fully condensed and aligned at the equatorial plate of the cell. Thus white blood cells or amniotic cells, stimulated into mitosis by phytohaemagglutinin and Figure 12.8. The autumn crocus Colchicium autumnale L., top left produces colchicine top right , a substance that can...

Immunoproteins

If you wish for peace, prepare for war. Latin proverb The human body is a nutrient rich environment and would be colonised rapidly by viruses, bacteria and other parasites if it were not protected by an immune system. This system not only recognises and destroys invading parasites and even cancer cells , but does not attack the bodies own cells. Both properties are equally important for our survival. An attack of our immune system against our own cells is called autoimmune disease. Such...

Equation for cooperative binding

Hill has proposed a mathematical model for co-operative binding in 1910 36 , long before the molecular causes of this phenomenon were discovered. He started with the assumption that several ligand molecules L bind to a protein P Then the equations for the association constant Ka and binding O become The latter equation can be linearised by rearrangement followed by taking logarithms log 1 -O n log L - log Kd 7.5 This is called the HlLL-equation, and a diagram of log vs log L is called...

Info

Fischer amp K. Zeile T. Svedberg Iron makes 0.334 of the weight of haemoglobin in all species. Thus haemoglobin is a defined molecule with a molecular weight of n 16700. isolates haem by treating haemoglobin with NaCl glacial acetic acid. The protein remains as colourless precipitate, the haem can by crystallised from the solution. suggests the name haemoglobin and crystallises it first crystallisation of a protein . measures oxygen binding to haemoglobin as...