SynopsisA conformational quantum-mechanical study of (Gly-Phe-Pro) and (Gly-Pro-Phe) repeating tripeptide sequences has been carried out with the PCILO method. Using appropriate molecules as a model, we investigated the conformational possibilities of each in sitn residue.Computations have been done taking into account the two typical pyrrolidine ring puckering and the most favorable orientations of the phenylalanyl side chain. Major conclusions drawn from this study are that the phenylalanyl can be accommodated a t both second and third positions in the sequence without preventing the formation of triple-helix conformation. However, the analogy observed between the rotational possibilities around the second residue of Gly-Pro-Pro and Gly-Phe-Pro indicates that phenylalanyl in the second position favors the triple-helix formation.
The title polytripeptides were synthesized and studied experimentally, by circular dichroism, and theoretically, by quantum mechanical methods. With the exception of poly(Gly‐Pro‐Val), which was found to be essentially structureless in solution, the other polymers adopt folded conformations, most probably of type II β‐bends. Conclusions from theoretical studies were generally in agreement with the experimental results. In particular, it is noteworthy that the optimized (φ, ø) maps for poly(Gly‐Pro‐Met) showed the absolute minimum (φ = 60°, ø = 0°) located inside the βII bend space.
Interaction between DNA and aminothiol radioprotectors has been proved to be purely peripheral, i.e., it does not affect the bases but solely the sugar-phosphate backbone. (This interaction is essentially electrostatic, between the phosphate sites and the radioprotector cationic groups.)In order to progress in the understanding of the conformational aspects of this interaction, we have carried out a quantum mechanical simulation of the approach by a cysteamine molecule of the DNA backbone.Major conclusions drawn from this study are: ( I ) The ab-inirio calculation of the charge distribution on the cysteamine radioprotector cation shows that this molecule possesses a positive NH3 head and SH tail. (2) The XILO energy variations of the supermolecule (dideoxyrihe-triphosphate + cysteamine) show minimal zones which enable us to specify the positions and the distortion of the cysteamine radioprotector in interaction with the DNA backbone.
PCILO results concerning the conformational possibility of the (Gly-PrePro) repetitive unit are presented. Using appropriate molecules as models, the conformational space of the various backbone dihedral angles was studied with the pyrrolidine rings left free to adopt the most favorable puckering. The results are in good agreement with available crystallographic data on collagenlike structures. These computations indicate that interchain interactions are only an additional stabilizing factor in triple-helix formation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.