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A helix ('hiːlɪks; ) is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is formed as two intertwined helices, and many proteins have helical substructures, known as alpha helices. The word helix comes from the Greek word ἕλιξ, "twisted, curved". A "filled-in" helix – for example, a "spiral" (helical) ramp – is a surface called helicoid. Properties and types The pitch of a helix is the height of one complete helix turn, measured parallel to the axis of the helix. A double helix consists of two (typically congruent) helices with the same axis, differing by a translation along the axis. A circular helix (i.e. one with constant radius) has constant band curvature and constant torsion. A conic helix, also known as a conic spiral, may be defined as a spiral on a conic surface, with the distance to the apex an exponential function of t

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Oligomerization of the alpha 1a- and alpha 1b-Adrenergic Receptor Subtypes: Potential Implications in Receptor Internalization

Susanna Cotecchia, Jean-Baptiste Perez, Laura Stanasila, Horst Vogel

We combined biophys., biochem., and pharmacol. approaches to investigate the ability of the a1a- and a1b-adrenergic receptor (AR) subtypes to form homo- and hetero-oligomers. Receptors tagged with different epitopes (hemagglutinin and Myc) or fluorescent proteins (cyan and green fluorescent proteins) were transiently expressed in HEK-293 cells either individually or in different combinations. Fluorescence resonance energy transfer measurements provided evidence that both the a1a- and a1b-AR can form homo-oligomers with similar transfer efficiency of .apprx.0.10. Hetero-oligomers could also be obsd. between the a1b- and the a1a-AR subtypes but not between the a1b-AR and the b2-AR, the NK1 tachykinin, or the CCR5 chemokine receptors. Oligomerization of the a1b-AR did not require the integrity of its C-tail, of two glycophorin motifs, or of the N-linked glycosylation sites at its N terminus. In contrast, helix I and, to a lesser extent, helix VII were found to play a role in the a1b-AR homo-oligomerization. Receptor oligomerization was not influenced by the agonist epinephrine or by the inverse agonist prazosin. A constitutively active (A293E) as well as a signaling-deficient (R143E) mutant displayed oligomerization features similar to those of the wild type a1b-AR. Confocal imaging revealed that oligomerization of the a1-AR subtypes correlated with their ability to co-internalize upon exposure to the agonist. The a1a-selective agonist oxymetazoline induced the co-internalization of the a1a- and a1b-AR, whereas the a1b-AR could not co-internalize with the NK1 tachykinin or CCR5 chemokine receptors. Oligomerization might therefore represent an addnl. mechanism regulating the physiol. responses mediated by the a1a- and a1b-AR subtypes. [on SciFinder (R)]

2003

Fluorescence Resonance Energy Transfer Shows a Close Helix-Helix Distance in the Transmembrane M13 Procoat Protein

Serge Cattarinussi, Horst Vogel

During the membrane insertion process the major coat protein of bacteriophage M13 assumes a conformation in which two transmembrane helixes corresponding to the leader sequence and the anchor region in the mature part of the protein coming into close contact with each other. Previous studies on the mol. mechanism of membrane insertion of M13 procoat protein have shown that this interaction between the two helixes might drive the actual translocation process. We investigated the intramol. distance between the two helixes of the transmembrane procoat protein by measuring fluorescence resonance energy transfer (FRET) between the donor (Tyr) placed in one helix and the acceptor (Trp) placed in the other helix. Various mutant procoat proteins with differently positioned donor-acceptor pairs were generated, purified, and reconstituted into artificial lipid bilayers. The results obtained from the FRET measurements, combined with mol. modeling, show that the transmembrane helixes are in close contact on the order of 1-1.5 nm. The present approach might be of general interest for detg. the topol. and the folding of membrane proteins. [on SciFinder (R)]

2001

Spectroscopy and Conformational Preferences of Gas-Phase Helices

Thomas Rizzo, Caroline Seaiby

We describe here a study of the spectroscopy of two peptides that we expect to be helical, Ac-Phe-(Ala)5-Lys-H+ and Ac-Phe-(Ala)10-Lys-H+, and one that we expect to be globular, Ac-Lys(H+)-Phe-(Ala)10, with the goal of identifying spectral features characteristic of their secondary structure. Conformation-specific IR-UV double resonance spectroscopy in a cold ion trap, together with nitrogen-15 isotopic substitution, allows us to identify four conformers of the smaller helix. Infrared spectra in the OH and amide NH stretch regions, together with theoretical calculations, provide diagnostics of the presence of helical structure as well as details of the specific hydrogen bonding patterns within the helix. The assigned vibrational spectra presented here provide a benchmark for the ability of theory to predict the spectrum of a helical peptide.

2009

DNA

Deoxyribonucleic acid (diːˈɒksᵻˌraɪboʊnjuːˌkliːᵻk,_-ˌkleɪ-; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic in

Protein

Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing met

Curve

In mathematics, a curve (also called a curved line in older texts) is an object similar to a line, but that does not have to be straight. Intuitively, a curve may be thought of as the trace left by

BIO-212: Biological chemistry I

Biochemistry is a key discipline for the Life Sciences. Biological Chemistry I and II are two tightly interconnected courses that aim to describe and understand in molecular terms the processes that make life possible.

BIO-105: Cellular biology and biochemistry for engineers

Basic course in biochemistry as well as cellular and molecular biology for non-life science students enrolling at the Master or PhD thesis level from various engineering disciplines. It reviews essential notions necessary for a training in biology-related engineering fields.

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Les constituants biochimiques de l'organisme, protéines, glucides, lipides, à la lumière de l'évolution des concepts et des progrès en biologie moléculaire et génétique, sont étudiés.