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Category: Microbial Genetics and Molecular Biology
The States, Conformational Dynamics, and Fusidic Acid-Resistant Mutants of Elongation Factor G, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555818142/9781555811846_Chap29-1.gif /docserver/preview/fulltext/10.1128/9781555818142/9781555811846_Chap29-2.gifAbstract:
This chapter summarizes the current knowledge and proposes a structural model for the function of elongation factor G (EF-G). The large number of mutations associated with fusidic acid resistance are an essential ingredient in this analysis. Recent investigations of a mutant EF-G with a different crystal packing have led to a complete interpretation of domain III at relatively low resolution. The functional cycle of EF-G can be described as a number of states both on and off the ribosome. The different states of EF-G may not necessarily be associated with different conformations of EF-G, but to the extent that there are different conformations, they will be related to different states. The density of EF-G could be identified with difference methods and compared to the crystallographic GDP conformation. The mutant G16V is fusidic acid sensitive compared to wt Thermus thermophilus EF-G, which is relatively resistant to the antibiotic. During one of the subsequent steps, EF-G adopts an open conformation like the one observed by cryo-EM. Since it overlaps the A-site tRNA, translocation must already have occurred, as is well known from studies of fusidic acid inhibition of protein synthesis. When EF-G has dissociated, it has the intermediate GDP conformation.
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Representation of some of the possible functional states of EF-G according to the classical model (a) and the model of Rodnina et al. (1997) (b). The white boxes represent the ribosome, the gray symbols represent EF-G in different states, and the black triangles represent GTP (base down) or GDP (base up).
Representation of some of the possible functional states of EF-G according to the classical model (a) and the model of Rodnina et al. (1997) (b). The white boxes represent the ribosome, the gray symbols represent EF-G in different states, and the black triangles represent GTP (base down) or GDP (base up).
Comparison of the two main conformations of EF-G observed crystallographically. The broad ribbon represents domains G, G′, and II, which here are fixed. The narrow tube represents domains III to V. The GDP conformation is shown in orange, and the new bent conformation of mutant H573A is shown in green. The red bar indicates the axis around which the rotation of about 10° occurs.
Comparison of the two main conformations of EF-G observed crystallographically. The broad ribbon represents domains G, G′, and II, which here are fixed. The narrow tube represents domains III to V. The GDP conformation is shown in orange, and the new bent conformation of mutant H573A is shown in green. The red bar indicates the axis around which the rotation of about 10° occurs.
Comparison of the structures of domains III and V. The same fold is observed. This fold, the RNA recognition motif (RRM), has also been observed in many ribosomal proteins.
Comparison of the structures of domains III and V. The same fold is observed. This fold, the RNA recognition motif (RRM), has also been observed in many ribosomal proteins.
Locations of fusidic acid-resistant mutations in EF-G (indicated in pink). The six most resistant mutants are shown in red. The right panel is an enlargement of the central region of the left panel.
Locations of fusidic acid-resistant mutations in EF-G (indicated in pink). The six most resistant mutants are shown in red. The right panel is an enlargement of the central region of the left panel.
Superposition of EF-G (van der Waals surface) in complex with GDP and the ternary complex of EF-Tu with tRNA and GDPNP (atomic model). The ternary complex has been found to have a somewhat more open conformation.
Superposition of EF-G (van der Waals surface) in complex with GDP and the ternary complex of EF-Tu with tRNA and GDPNP (atomic model). The ternary complex has been found to have a somewhat more open conformation.
Comparison of the observed conformations of EF-G with those of the ternary complex of EF-Tu. Fus, fusidic acid; kirr, kirromycin; aa-tRNA, aminoacyl-tRNA.
Comparison of the observed conformations of EF-G with those of the ternary complex of EF-Tu. Fus, fusidic acid; kirr, kirromycin; aa-tRNA, aminoacyl-tRNA.