The glutathione S-transferases (GST) represent a major group of detoxification enzymes. All eukaryotic species possess multiple cytosolic and membrane-bound GST isoenzymes, each of which displays distinct catalytic as well as noncatalytic binding properties: the cytosolic enzymes are encoded by at least five distantly related gene families (designated class alpha, mu, pi, sigma, and theta GST), whereas the membrane-bound enzymes, microsomal GST and leukotriene C, synthetase, are encoded by single genes and both have arisen separately from the soluble GST. Evidence suggests that the level of expression of GST is a crucial factor in determining the sensitivity of cells to a broad spectrum of toxic chemicals. In this article the biochemical functions of GST are described to show how individual isoenzymes contribute to resistance to carcinogens, antitumor drugs, environmental pollutants, and products of oxidative stress.A description of the mechanisms of transcriptional and posttranscriptional regulat...

The glutathione S-transferase supergene family: regulation of GST and the contribution of the isoenzymes to cancer chemoprotection and drug resistance.

The Cationminus signpi Interaction.

A wealth of protein and DNA sequence data is being generated by genome projects and other sequencing efforts. A crucial barrier to deciphering these sequences and understanding the relations among them is the difficulty of detecting subtle local residue patterns common to multiple sequences. Such patterns frequently reflect similar molecular structures and biological properties. A mathematical definition of this "local multiple alignment" problem suitable for full computer automation has been used to develop a new and sensitive algorithm, based on the statistical method of iterative sampling. This algorithm finds an optimized local alignment model for N sequences in N-linear time, requiring only seconds on current workstations, and allows the simultaneous detection and optimization of multiple patterns and pattern repeats. The method is illustrated as applied to helix-turn-helix proteins, lipocalins, and prenyltransferases.

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Detecting Subtle Sequence Signals: A Gibbs Sampling Strategy for Multiple Alignment

The lipocalin protein family is a large group of small extracellular proteins. The family demonstrates great diversity at the sequence level; however, most lipocalins share three characteristic conserved sequence motifs, the kernel lipocalins, while a group of more divergent family members, the outlier lipocalins, share only one. Belying this sequence dissimilarity, lipocalin crystal structures are highly conserved and comprise a single eight-stranded continuously hydrogen-bonded antiparallel beta-barrel, which encloses an internal ligand-binding site. Together with two other families of ligand-binding proteins, the fatty-acid-binding proteins (FABPs) and the avidins, the lipocalins form part of an overall structural superfamily: the calycins. Members of the lipocalin family are characterized by several common molecular-recognition properties: the ability to bind a range of small hydrophobic molecules, binding to specific cell-surface receptors and the formation of complexes with soluble macromolecules. The varied biological functions of the lipocalins are mediated by one or more of these properties. In the past, the lipocalins have been classified as transport proteins; however, it is now clear that the lipocalins exhibit great functional diversity, with roles in retinol transport, invertebrate cryptic coloration, olfaction and pheromone transport, and prostaglandin synthesis. The lipocalins have also been implicated in the regulation of cell homoeostasis and the modulation of the immune response, and, as carrier proteins, to act in the general clearance of endogenous and exogenous compounds.

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The lipocalin protein family: structure and function

This paper describes the development of a simple empirical scoring function designed to estimate the free energy of binding for a protein-ligand complex when the 3D structure of the complex is known or can be approximated. The function uses simple contact terms to estimate lipophilic and metal-ligand binding contributions, a simple explicit form for hydrogen bonds and a term which penalises flexibility. The coefficients of each term are obtained using a regression based on 82 ligand-receptor complexes for which the binding affinity is known. The function reproduces the binding affinity of the complexes with a cross-validated error of 8.68 kJ/mol. Tests on internal consistency indicate that the coefficients obtained are stable to changes in the composition of the training set. The function is also tested on two test sets containing a further 20 and 10 complexes, respectively. The deficiencies of this type of function are discussed and it is compared to approaches by other workers.

Empirical scoring functions: I. The development of a fast empirical scoring function to estimate the binding affinity of ligands in receptor complexes

Publisher Summary This chapter focuses on the structural analyses and comparisons between members of a multigene family of hydrophobic ligand-binding proteins. It discusses the structural motif, general characteristics of the binding cavity, ligand entry, and the portal hypothesis and provides a detailed comparison of intra- and extracellular lipid binding proteins with known crystal structures. The members of this family are referred as lipid-binding proteins (LBPs). This collection of proteins can be subdivided into two groups: the intracellular lipid-binding protein family (iLBP) and the extracellular lipid binding protein family (eLBP). The comparison primarily deals with the iLBP branch because this family is becoming structurally well characterized. However, the structural comparisons are extended to some members of the eLBP family because the basic structural motif used to bind hydrophobic ligands applies to both. The products of hydrolysis of the intestinal lipids, including fatty acids, cholesterol, monoglycerides, and lysophospholipids, have very low solubilities and are absorbed by biliary micelles in the gut. These micelles diffuse through the glycocalyx, which stabilizes an unstirred water layer at the surface of the enterocyte. The chapter concludes with a discussion of the results of site-directed mutagenesis studies, the thermodynamics of lipid binding, and considerations of protein stability and folding.

Lipid-Binding Proteins: A Family of Fatty Acid and Retinoid Transport Proteins

Structure determination and refinement of human alpha class glutathione transferase A1-1, and a comparison with the Mu and Pi class enzymes.

Human serum retinol binding protein (RBP) in complex with retinol has been crystallographically refined to an R-factor of 181% with 2A resolution data The protein topology results in an anti-parallel beta-barrel that encapsulates the retinol ligand A detailed description of the protein and the binding site is provided Our structural work has helped to define a family of proteins, many of which are carrier proteins for smaller ligand molecules We describe the structural basis for the conservation of sequence within the family

Crystallographic refinement of human serum retinol binding protein at 2A resolution.

Crystallographic Studies on a Family of Cellular Lipophilic Transport Proteins: Refinement of P2 Myelin Protein and the Structure Determination and Refinement of Cellular Retinol-binding Protein in Complex with All-trans-retinol

S. W. Cowan

Papers

Lipid-Binding Proteins: A Family of Fatty Acid and Retinoid Transport Proteins

Structure determination and refinement of human alpha class glutathione transferase A1-1, and a comparison with the Mu and Pi class enzymes.

Crystallographic refinement of human serum retinol binding protein at 2A resolution.

Crystallographic Studies on a Family of Cellular Lipophilic Transport Proteins: Refinement of P2 Myelin Protein and the Structure Determination and Refinement of Cellular Retinol-binding Protein in Complex with All-trans-retinol

Crystallization of GST2, a human class alpha glutathione transferase