Zipper molecule

Thus, 38 reacts with benzaldehyde and sarcosine (toluene, 110 °C, 20 h) to give a mixture of cycloadducts 39 and 40. The endd-cycloadduct 39 is hydrostannylated in situ, in the presence of zipper molecule 33a to afford 41 in 66% yield as a 1 1 mixture of diastereoisomers (Scheme 5.6.10). Overall, the two-step protocol combines six reactants and delivers 41, in which two rings, four C—C bonds, one C—N bond, and four stereocentres and one tetra-substimted C-centre have been formed. 

Use of a zipper molecule with aryl iodide and double-bond functionaHties [77] leads to a significant increase in molecular complexity, the overall sequence resulting in the formation of five bonds, five stereocenters, two rings, and a tetrasubstituted carbon center. 

In a further development [78], the zipper molecule with an aryl iodide func-tionahty was bound to a Wang resin the Suzuki chemistry was also used, and three small libraries of 16 compounds were prepared. 

A novel, three-component, palladium-catalyzed, cascade cyclization-anion-capture process which involves in situ generation of a zipper molecule has been reported. Thus, 2-iodobenzoyl chloride, an acetophenone imine, and carbon monoxide react in the presence of Pd(PPh3)2Cl2 to give isoindolin-l-one in moderate yield (eq 86). 

Residues 50-64 of the GAL4 fragment fold into an amphipathic a helix and the dimer interface is formed by the packing of these helices into a coiled coil, like those found in fibrous proteins (Chapters 3 and 14) and also in the leucine zipper families of transcription factors to be described later. The fragment of GAL4 comprising only residues 1-65 does not dimerize in the absence of DNA, but the intact GAL4 molecule does, because in the complete molecule residues between 65 and iOO also contribute to dimer interactions. 

The classical cadherins are translated as precursor because they are N-terminally cleaved to reveal the mature proteins. This processing is required to activate the cell adhesion function of cadherins. Cadherins interact in trans (i.e., from opposite cells) via the most N-terminal cadherin rqDeats. A short amino acid sequence within this repeat, histidine-alanine-valine (HAV), has been implicated in mediating cell-cell contacts as HAV peptides can disrupt cadherin-dependent cell adhesion. Besides the trans-interactions of cadherins, the extracellular domains are also capable of forming cis-dimers through lateral amino acid contacts between cadherin molecules on one cell. This dimerization again mainly involves the first cadherin repeat. A zipper model based on the pattern of alternating cis- and trans-dimers [1] for the adhesive interactions has been proposed. 

A leucine zipper is a structural motif present in a large class of transcription factors. These dimeric proteins contain two extended alpha helices that grip the DNA molecule much like a pair of scissors at adjacent major grooves. The coiled-coil dimerization domain contains precisely spaced leucine residues which are required for the interaction of the two monomers. Some DNA-binding proteins with this general motif contain other hydrophobic amino acids in these positions hence, this structural motif is generally called a basic zipper. 

A recent crystal structure based model [20] for the structure of C-cadherin postulates that the five extracellular domains EC1-EC5 protrude from the cell surface as a curved rod. The structural analysis of C-cadherin reveals that the molecules facing each other across apposed cell surfaces are antiparallel to one another, forming a dimeric interaction termed a strand dimer (Fig. 7-5). This forms the functional unit that is likely to mediate adhesion between cell surfaces. The structure from this recent paper allows the prediction of both cis and trans interfaces that together result in a lattice and not, as previously believed, an adhesion zipper. This new model allows for a mechanism by which adhesion plates or puncta might be generated, such as are formed at CNS synapses [21, 22], adherens junctions and desmosomes [23], all cadherin based organelles. 

The spatial conformation that the ligand-receptor acquires, particularly the spatial disposition that helix 12 of the LBD attains when it binds to estradiol, is key for the subsequent recruitment of the transcription cofactors (Fig. 1.9). Indeed, the arrival of estradiol restructures the entire domain, making helix 12 rotate and close the hole where the leucine zipper sequence of the corepressor had been lodged before (Fig. 1.10). Consequently, both molecules, corepressor and receptor, lose their affinity and their bond is undone. Another structure capable of interacting with gene transcription coactivators is formed at the same place on the receptor (MacGregor et al. 1998 McDonnell et al. 2002). 

For most collagens, the folding of the triple helical domain proceeds from the carboxyl end toward the amino end of the trimeric molecule in a zipper-like fashion with a rate that is limited by cis—trans isomerization of peptidyl prolyl bonds." The fast propagation of the triple helix formation is followed by a slower folding... 

The bases are numbered outward from the central C and G.) The small solid spheres are water molecules. Notice the water mediated interactions of the basic arginine and lysine side chains with the nucleic acid bases and also the interaction of R240 and R243 (in B) with a backbone phosphate. The overall structure of the protein is similar to that of another leucine zipper shown in Fig. 2-21. From Keller et al.419 Drawings courtesy of Timothy J. Richmond. 

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