The conformational properties of elongation factor G and the mechanism of translocation

被引:55
作者
Czworkowski, J
Moore, PB
机构
[1] YALE UNIV,DEPT COMP SCI,NEW HAVEN,CT 06520
[2] YALE UNIV,DEPT MOL BIOPHYS & BIOCHEM,NEW HAVEN,CT 06520
关键词
D O I
10.1021/bi970610k
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The elongation phase of protein synthesis is promoted by two G proteins, elongation factor Tu (EF-Tu), which delivers aminoacyl tRNAs to the ribosome, and elongation factor G (EF-G), which catalyzes translocation. Crystallographic investigations have revealed that EF-G.GDP resembles the EF-Tu.GTP (aminoacyl tRNA) complex, and it has been proposed that the translocase function of EF-G is derived from this similarity [Nissen, P., et al. (1995) Science 270, 1464]. However, its significance is uncertain because the affinity of EF-G.GDP for the ribosome is much lower than that of the ternary complex it resembles and because EF-Tu GDP, the form of EF-Tu that has low ribosome affinity, has a conformation radically different from that of EF-Tu.GTP or EF-Tu in the ternary complex. The small-angle X-ray scattering study described here was undertaken to ascertain if the form of EF-G that has high ribosome affinity, EF-G.GTP, the structure of which is unknown, could be a mimic of EF-Tu GDP. The data show that nucleotide-free EF-G, EF-G.GDP, EF-G.GTP, and EF-G.GMPPCP cannot be distinguished by solution scattering and that it is likely they all resemble crystalline EF-G.GDP. Since an EF-Tu-like change would easily have been detected, it follows that it does not occur in EF-G. These observations have significant implications for the mechanism of translocation.
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页码:10327 / 10334
页数:8
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