Biomedical subjects

H Luecke

Publications and source records attributed to H Luecke.

6 recordsLinked to original sources

PubMed1992

Crystallization and preliminary crystallographic characterization of GTP cyclohydrolase I from Escherichia coli.

GTP cyclohydrolase I of Escherichia coli has been purified from a recombinant bacterial strain. The enzyme was crystallized from 0.6 M-sodium citrate and from 0.8 M-sodium/potassium phosphate, respectively. Crystals grown in citrate showed X-ray diffraction extending to a resolution better than 3 A. The space group was P2(1) with cell dimensions a = 204.8 A, b = 210.1 A, c = 72.2 A, alpha = gamma = 90 degrees and beta = 95.8 degrees.

Biopterins↗

PubMed1992

Crystal and molecular structure of human annexin V after refinement. Implications for structure, membrane binding and ion channel formation of the annexin family of proteins.

Two crystal forms (P6(3) and R3) of human annexin V have been crystallographically refined at 2.3 A and 2.0 A resolution to R-values of 0.184 and 0.174, respectively, applying very tight stereochemical restraints with deviations from ideal geometry of 0.01 A and 2 degrees. The three independent molecules (2 in P6(3), 1 in R3) are similar, with deviations in C alpha positions of 0.6 A. The polypeptide chain of 320 amino acid residues is folded into a planar cyclic arrangement of four repeats. The repeats have similar structures of five alpha-helical segments wound into a right-handed compact superhelix. Three calcium ion sites in repeats I, II and IV and two lanthanum ion sites in repeat I have been found in the R3 crystals. They are located at the convex face of the molecule opposite the N terminus. Repeat III has a different conformation at this site and no calcium bound. The calcium sites are similar to the phospholipase A2 calcium-binding site, suggesting analogy also in phospholipid interaction. The center of the molecule is formed by a channel of polar charged residues, which also harbors a chain of ordered water molecules conserved in the different crystal forms. Comparison with amino acid sequences of other annexins shows a high degree of similarity between them. Long insertions are found only at the N termini. Most conserved are the residues forming the metal-binding sites and the polar channel. Annexins V and VII form voltage-gated calcium ion channels when bound to membranes in vitro. We suggest that annexins bind with their convex face to membranes, causing local disorder and permeability of the phospholipid bilayers. Annexins are Janus-faced proteins that face phospholipid and water and mediate calcium transport.

Amino Acid Sequence↗

PubMed1992

Annexin V-crystal structure and its implications on function.

Annexins constitute a family of cytosolic, water soluble proteins, which bind to negatively charged phospholipids in a calcium-dependent manner. They display structural and functional features of both soluble and integral membrane proteins. The annexins face the hydrophilic as well as the hydrophobic phase (Janus-faced proteins) and mediate ion transport in vitro. We present the refined structure and molecular model of annexin V at 2.0 A resolution. The molecule is almost entirely alpha-helical, and each of the four repeats of annexin V is folded into a compact domain of similar structure. The four domains are arranged in an almost planar, cyclic array. In the center of the molecule, one can find a prominent hydrophilic pore, which we associate with the calcium-selective channel found in annexin V. Annexin V has an overall flat, slightly curved shape with two faces, one convex and one concave. The three calcium binding sites Ca1 to Ca3, all located at the convex face of the molecule, are assumed to be phospholipid binding sites, as suggested by their structural similarity to the calcium site of phospholipase A2. Soluble and membrane-bound annexin have closely similar structures, as shown by electron microscopic analysis. Several other observations provide evidence that the membrane-anchoring region of the annexin V molecule is located on the convex face. In the last part of this article, the electrophysiology of the annexins is described. Ion permeation occurs in discrete conductance states and is regulated by voltage across the membrane. A model for the annexin V-membrane interaction, the ion channel formation, and the ion conduction pathway is proposed.

Amino Acid Sequence↗

PubMed1991

Dipoles localized at helix termini of proteins stabilize charges.

The charge-stabilization effect associated with alpha-helices in proteins has been reexamined by microscopic calculations without any a priori assumptions about the dielectric constant of the protein. The calculations reproduce the observed charge stabilization effect of a helix in two well-defined test cases: a histidine residue situated at the C-terminal end of a helix in barnase and the sulfate ligand located near the N-terminal end of a helix of the sulfate-binding protein. They also show that the effective dielectric constant for helix-charge interactions is much larger than previously assumed and that the stabilizing effect of the helix is not associated with the helix macrodipole but rather with a few localized dipoles confined mostly to the first turn of the helix. It is predicted that mutations at one end of the helix should have very small effects on the stabilization of charges at the opposite terminus. It is pointed out that the relatively short-ranged effect of the helix is essentially similar to other cases in which localized dipoles play key roles in electrostatic stabilization.

Bacterial Proteins↗

PubMed1990

High specificity of a phosphate transport protein determined by hydrogen bonds.

Transport of the essential nutrient phosphorus--primarily in the form of orthophosphate--into cells and organelles is highly specific. This is exemplified by the uptake of phosphate or its close analogue arsenate by bacterial cells by way of a high affinity active transport system dependent on a phosphate-binding protein; this system is unable to recognize other inorganic oxyanions and is, moreover, distinct from the one for sulphate transport. The phosphate-binding protein is a member of a family of periplasmic proteins acting as initial high-affinity receptors for the osmotic shock-sensitive active transport systems or permeases for various sugars, amino acids, oligopeptides, and oxyanions. We report here the highly refined 1.7 A resolution X-ray structure of the liganded form of the phosphate-binding protein. The structure reveals the atomic features responsible for phosphate selectivity, either in monobasic or dibasic form, and the exclusion of sulphate. These features are fundamental to understanding phosphate transport systems and molecular recognition of charged substrates or ions in other biological processes.

Arsenates↗

PubMed1986

Crystallization and x-ray diffraction studies of a phosphate-binding protein involved in active transport in Escherichia coli.

We have obtained single crystals of a phosphate-binding protein (Mr = 34,400) that serves as initial receptor in osmotic shock-sensitive active transport in Escherichia coli. The crystals, suitable for high resolution crystallographic analysis, belong to the space group P2(1)2(1)2(1). The unit cell has dimensions of a = 41.97, b = 64.66, and c = 124.6 A and contains four protein molecules. Including this phosphate-binding protein, there are now a total of six different binding protein structures currently under investigation in our laboratory, the others being those specific for L-arabinose, D-galactose, D-maltose, sulfate, or leucine/isoleucine/valine.

Carrier Proteins↗