Peptide short-bridged

The plot of In fcgt vs. the number, n, of Pro residues (Figure 1) demonstrates that for longer hnear peptides (n = 3-5), the rate of electron transfer decreases exponentially with growing n. However, the k t data for shorter (n = 0-2) hnear peptides fall off considerably from the plot extrapolated to lower n values. This indicates that the rate of LRET in short-bridged peptides is faster than would be expected on the assumption of a common mechanism of electron transfer in the whole group of peptides. In order to rationahze these findings in terms of the theory of the distance dependence of LRET kinetics (33, 34), the separation distances and spatial disposition of the aromatic side chains in the hnear peptides studied had to be evaluated from their conformational preferences and conformational dynamics. 

The great difference in slopes for short-bridged peptides between the two systems can be rationalized in terms of differences in the nuclear part of the p descriptor. In the charged metallo systems with n = 1-3 prolines, the rates of intra-molecular electron transfer decrease rapidly by about 3 orders of magnitude. For these systems, the LRET mechanism is largely under the control of the nuclear factor (Pn = 9.5 nm" and Pei = 6.5 nm ) (10). The much smaller distance dependence of fcet in the Trp -Tyr system for peptides with n = 0-2, associated largely with the TS pathway and weak nuclear control, is consistent with the neutral character of the Tip and Tyr radicals involved in LRET and, thus, the low value of Xout (3). 

By far the most studied family of the G-protein-coupled receptors are the rhodopsin-like receptors. These are also the largest group of receptors in number as they include receptors not only for the monoamines, nucleotides, neuropeptides and peptide hormones, but they also include the odorant receptors which number several hundreds of related receptors. These receptors have short N-termini, a conserved disulphide bridge between the TM2-TM3 and TM4—TM5 extracellular domains, and variable-length C-termini. In some cases the C-terminus is myristolyated which by tying the C-terminus to the cell membrane generates a fourth intracellular loop. 

Since an increased number of disulfide bridges in relatively short polypeptide chains leads to compact globular structures with the disulfides mainly buried in the nonpolar core, such excised protein fragments should represent, even in the precursor molecules, stable subdomains. Therefore, sufficient structural information can be retained for a correct refolding at least to some extent, if appropriate experimental conditions are applied in terms of peptide concentration, redox reagents, temperature and/or reaction buffers. A great deal of... 

Baldwin and co-workers [4] have made a pioneering contribution in this area. They demonstrated that short (11-15 residues) alanine-rich peptides (such as 1), having several glu-lys salt bridges adopt a stable monomeric a-helix structure in solution. 

Neurotoxins of scorpions especially represent ion channel toxins that mainly affect sodium and potassium channels. Several compounds represent neurotoxins that are directed selectively against insects.97 Na+ channel-specific a-, (3-, and 7-toxins are composed of 58-76 amino acids and contain four stabilizing disulfide bridges.98 The well-studied K+ channel-specific toxins (divided into at least nine distinct peptide subfamilies) bind to the extracellular face of the channel and comprise 29-39 amino acids stabilized by 3-4 disulfide bridges.99 Various Ca2+ channel scorpion toxins, antimicrobial peptides, and short insectotoxins active on Cl channels have been found.96... 

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