Die Verknüpfung funktioneller und struktureller Informationen über G-Protein-gekoppelte Rezeptoren (GPCRs) ist für das Verständnis dieser komplexen Systeme von Vorteil. Wir beschreiben hier die Modellierung von GPCRs mit der Software ROSETTA, wobei auch flexible Regionen abgebildet werden.Combination of functional and structural information of G-protein coupled receptors (GPCRs) aids the understanding of these complex systems.Here we describe modeling of GPCRs using the ROSETTA software suite, which also covers variable regions like loops or termini.

The formation of -turns is a possibility to reverse the direction of peptide sequences via five amino acids. In this paper, a systematic conformational analysis was performed to find the possible isolated -turns with a hydrogen bond between the first and fifth amino acid employing the methods of ab initio MO theory in vacuum (HF/6-31G*, B3LYP/6-311+G*) and in solution (CPCM/HF/6-31G*). Only few -turn structures with glycine and alanine backbones fulfill the geometry criteria for the i(i+4) hydrogen bond satisfactorily. The most stable representatives agree with structures found in the Protein Data Bank. There is a general tendency to form additional hydrogen bonds for smaller pseudocycles corresponding to -and -turns with better hydrogen bond geometries. Sometimes, this competition weakens or even destroys the i(i+4) hydrogen bond leading to very stable double -turn structures. This is also the reason why an "ideal" -turn with three central amino acids having the perfect backbone angle values of an -helix could not be localized. There are numerous hints for stable -turns with a distance between the C  -atoms of the first and fifth amino acid smaller than 6-7 Å, but without an i(i+4) hydrogen bond.

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