Dimers antiparallel

Fig. 11a,b. Examples of one and two-dimensional structures for terminally fluorinated mesogens a antiparallel dimeric layering for the compounds with one terminal fluorinated tail (Diele et al. [38]) b two-dimensional (columnar) packing observed for the swallow-tailed fluorinated compounds solid lines indicate two-dimesional rectangular lattice (Lose et al. [41])... 

A detailed oxidation study on an artificially designed palindromic peptide with a predicted high tendency to form antiparallel a-helices confirmed that stabilization of the a-helix by increasing amounts of TFE allowed the control of the product distribution in favor of the antiparallel dimer to a certain degree, although increasing amounts of cyclic trimers were formedi106 In the absence of or at low levels of TFE, formation of the cyclic monomer was predominant. 

VIP 1 Basement membranes Long-chain, antiparallel dimers, anchoring fibrils ... 

Synthetic FI was treated using conditions known to convert oxytocin to a mixture of parallel and antiparallel dimers RPLC separation gave FI (20.1 min) and two more retained peaks at 42.0 and 45.3 min. The latter were analyzed by size-exclusion LC both had 1,570. 

To ascertain the relative configurations of the dimers, each was synthesized specifically, using protecting groups that allow directed formation of disulfide bonds. Comparison of retention behavior of the specifically synthesized dimers with those synthesized non-specifically showed that F2 corresponds to the antiparallel dimer (Fig. 1) and the slower eluting component to the parallel isomer. 

To check whether the diuretic hormone acts on Malpighian tubules via cAMP, intact tubules were incubated with synthetic F2 for various periods of time, then extracted and assayed for cAMP using an RIA. Addition of the synthetic antiparallel dimer elevated tissue cAMP concentration at all times tested. 

These data show the presence in subesophageal and thoracic ganglia of Locusta of an antiparallel dimeric peptide (F2), which was called the AVP-like insect diuretic hormone (AVP-like DH) (H). The sequence homology between the AVP-like DH and the vertebrate neurohypophyseal peptides is strong Cys-(2)-(3)-(4)-Asn-Cys-Pro-(8)-Gly-NH2. The AVP-like DH and AVP differ only at positions 2, 3, and 4, whereas the homology to the ancestral molecule arginine vasotocin is even stronger, with differences restricted to positions 2 and... 

Moreover, the existence of a neuropeptide as a dimer had only two precedents. Transforming growth factor-Ii, a dimer (X2.) r is encoded by a gene containing one copy of the 112-amino acid monomer. li-Human atrial natriuretic polypeptide is an antiparallel dimer of the 28-amino acid a-human atrial polypeptide (H). The latter dimer also coexists in tissue with its corresponding monomer, a situation analogous to FI and F2. 

Wille H, Diewes G, Biemat J, Mandelkow EM, Mandelkow E (1992) Alzheimer-like paired helical filaments and antiparallel dimers formed from microtubule-associated protein tau in vitro. J Cell Biol 118 573-584... 

The amphiphilic helical structure of most antibacterial peptides is a prerequisite for theu propensity to form chaimels across the double-layered biological membranes (12). In aqueous solution, positions a and d of the a-helical heptad repeat (a, b, c, d, e, f g) ( 3) require hydrophobic residues for the onset of the widespread antiparallel dimer (or multimer) superstructure (a-helix coiled coU) (14—16) (Fig. 2). The hydrophilic positions e and g, immediately on the back, reinforce the dimer stability... 

Figure 15.2 Helical wheel and sequence representation of the antiparallel, dimeric model system. The substitution positions are highlighted in one strand with an open square for the hydrophobic core and an open circle for the charged domain. Their direct interaction partners in the opposite strand are shaded in gray squares or circles, respectively. The ligation site is marked with an arrow.

The length of the antiparallel overlap between molecules in a side-polar filament is not firmly established. A 43-nm antiparallel overlap was unique to segments formed from smooth muscle myosin rods by precipitation with divalent cations (Kendrick-Jones et al., 1971). Folded dimers with an approximately 40- to 50-nm antiparallel overlap are formed at salt concentrations <50 mM KCl (Trybus and Lowey, 1984). Both of these observations suggest that the molecule favors a 43-nm overlap. Measurements obtained by scanning transmission electron microscopy, however, show that filaments formed in vitro have one antiparallel dimer per 14.3 nm of filament length, a value that favors a model where adjacent molecules have a 14.3-nm antiparallel overlap (Cross and Engel, 1991) (Fig. 4). The... 

Molle et al. (243) synthesized the 22-residue transmembrane segment of the essential subunit 8 of the Saccharomyces cerevesiae H+ ATP synthetase and observed weakly voltage-dependent conductance levels on different planar lipid bilayers. CD spectra show 60% a-helix for this peptide in low dielectric solvents. The conductance exhibited a second-order concentration dependence, suggestive of antiparallel dimers as the conducting unit (243). 

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