Triple helix formation

Kinetic Aspects of Triple-Helix Formation of Peptide Models Compared with... 

Since these investigations could be carried out only in the crystalline state, the question of the dynamics of the triple-helix formation and of the correlation of its stability with the amino acid sequence could be answered only with the help of other methods working in solution. 

It is well known that native collagen containes tripeptide sequences, which alone are not capable of building up a triple helix (e.g. Gly-Pro-Leu, Gly-Pro-Ser) when they exist as homopolypeptides. The synthesis of threefold covalently bridged peptide chains opens up the possibility of investigating the folding properties of such weak helix formers, because the bridging reduces the entropy loss during triple-helix formation and thereby increases the thermodynamic stability of the tertiary structure. Therefore, we have... 

This gives an important hint at what kind of model peptides are synthesized to obtain detailed information about the thermodynamics and kinetics of the collagen triple-helix formation. A first success was already achieved by synthesizing peptides of the following general structure37 ... 

This model does not say anything about the mechanism of triple-helix formation, because even in the case of an AON mechanism, nucleation may take place at many positions of the chains and may lead to products the chains of which are staggered. The AON model is based on the assumption that these products are too instable to exist in measurable concentration. As already mentioned, Weidner and Engel142 succeeded in proving by relaxation measurements of al CB2 that the kinetics of in vitro triple-helix formation is governed by more than one relaxation time. This rules out an AON mechanism, but the fitting to the experimentally found equilibrium transition curves nevertheless showed good accommodation and AH° computed from these curves could be confirmed by calorimetric measurement. 

According to Eq. (1), the triple-helix formation can be imagined as a process which may be divided into 3n - 2 steps of equilibrium with the same values of Aand AS each. This means that AG° is a linear function of 3n - 2 for the whole process. 

The covalent bridging of the three polypeptide chains with the sequence Ala-Gly-Pro has facilitated, as expected, the nucleation step for triple-helix formation. This is also... 

Fig. 37. Dependence of the thermodynamic parameters AH and AS of triple-helix formation on the imino acid content of the peptides (obtained by cleavage of calf skin-type I collagene with cyanogene and subequent isolation by column chromatrography)3) and of the native neutral salt-soluble skin collagene of various animals. The entropy values are denoted by dotted lines...

Fig. 39. Dependence of AHC of triple-helix formation on the proline content of the CNBr peptides and synthetic model peptides, respectively...

Moser H.E., Dervan P.B. Sequence-specific cleavage of double helical DNA by triple helix formation. Science 1987 238 645-650. 

Steinmann, B., Bruckner, P. and Superti-Furga, A. (1991) Cyclosporin A slows collagen triple-helix formation in vivo indirect evidence for a physiological role of peptidyl prolyl cis-trans isomer use. Journal ofBiological Chemistry 266,1299-1303. 

Geselowitz, D.A., and Neumann, R.D. (1995) Quantitation of triple-helix formation using a photo-cross-linkable aryl azide/biotin/oligonucleotide conjugate. Bioconjuate Chem. 6, 502-506. 

Triphenyltin, as skin irritant, 24 829 Triphenyltin hydroxide, 24 817 as eye irritant, 24 829 Triphenymethane soluble dyes, 7 373t Triphosphorus pentanitride, 79 57 Triple bottom line, 72 807 Triple-bond stretching, 74 235 Triple helices, 77 609 Triple-helix formation, 77 528 Triple-jet crystal growth methods,... 

Neves C, Byk G, Scherman D, Wils P. Coupling of a targeting peptide to plasmid DNA by covalent triple helix formation. FEBS Lett 1999 453 41-45. 

Collagen Chain Selection, Trimerization, and Triple Helix Formation 506... 

So far, the function of lysyl hydroxylation and glycosylation of Hyls is not clear. In some diseases such as 01, an overmodification of lysine residues occurs. It has been postulated that the triple helix formation is slower in these cases and therefore the unfolded chains are exposed for a longer time to the modifying enzymes. 

Disulfide bond formation within the individual propeptides precedes folding and trimers are then formed by association of the C-terminal propeptides." Disulfide bonds between the chains are then formed and this formation is most likely catalyzed by PDI." As triple helix formation proceeds, the rate-limiting step in this process is the cis—trans isomerization of peptidyl-Pro bonds. This process can be catalyzed by peptidyl-prolyl cis—trans isomerases (cyclophilins and FKBPs). This activity is required to convert the proline residues to the trans form required for triple helix formation." " " ... 

In native collagen, all Gly-Pro and Xaa-Hyp peptide bonds are in the trans conformation, whereas in the unfolded state, a significant fraction of cis isomers populates at each Gly-Pro and Xaa-Hyp peptide bond, cis-to-trans isomerization reactions at prolyl peptide bonds are the origin for the observed slow kinetics of triple helix formation" as shown by their high activation energy ( 72 kj moG )" and their acceleration by prolyl... 

C-terminal NC domain (NC2)." The deletion of the N-terminal NC domain (NCI) did not abolish the triple helix formation and subsequent association of two molecules into disulfide-bonded hexameric aggregates," an... 

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... 

Each of the three strands of the collagen triple helix is based upon the poly(Pro)II helix. Numerous studies of peptides capable of triple helix formation have been performed, and these have been reviewed 149 The CD of the collagen triple helix1146 is qualitatively like that of the poly(Pro)II, but the position of the maximum depends on the content of secondary vs tertiary peptide bonds. In natural collagen, the positive band is at about 220 nm and the negative band at 197 nm. 

Strobel, S. A., L. A. Doucette-Stamm, L. Riba, D. E. Hous-man, P. B. Dervan, Site-specific cleavage of human chromosome 4 mediated by triple-helix formation. Science 254 1639-1642, 1991. 

Triple helix formation expands the catalytic repertoire of template induced oligopeptide formation beyond simple autocatalysis since reaction networks of the hypercycle type (Eigen8 and Schuster, 1979) can be designed with this reaction too. 

Transport inhibitors, dinitrophenol, DNP, 257 fluorodinitrobenzene, FDNB, 251 gramicidin, 255 N-ethylmaleimide, NEM, 250 ouabain, 259, 260 tetraethyl ammonium, TEA, 253 tetrodotoxin, 254, 256 Trifolium subterranean, migration of, 213, 214 Triple helix formation, 141 Two genes, one polypeptide, 2,59... 

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