| Abstract |
In this thesis, a combined theoretical and experimental study of the 4-a-helical bundle protein tertiary motif is presented. The distributions of the c1, c2 dihedral angles in this motif have been determined and compared with those observed in globular proteins. This analysis suggests that: (i) The side-chains conformations in 4-a-helical bundles are limited to a subset of the conformations that are observed in globular proteins.(ii) The distribution of Tyr residues shows a novel cluster in the c1, c2 conformational space. (iii) At least for Tyr and Ile, the conformational preferences of side-chains are position-dependent. This dependence can be rationalized in terms of the heptad concept used to describe the topology of 4-a-helical bundles. Natural mutations in 4-a-helical bundles follow a pattern that can be rationalized by the preferred side-chains conformations in this motif. RM6, a Rop mutant with a five-residue deletion at the loop region has been crystallized and crystallographic data extending to a 2.0A resolution have been collected. From this data set which represents a considerable improvement from the previous data to 2.3A an electron density map has been calculated and we improved significantly the existent atomic model for the protein. Our efforts to further improve the crystallization conditions for Rop mutant RM7 (a mutant with a two residue insertion of the loop) we crystallized an unknown protein XP. For the XP protein we have determined its molecular weight (18482Da). Experiments for its identification are in progress.
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Υπολογιστικές και Δομικές μελέτες 4-α-Ελικοειδών δεματίων
