GTP‐binding Loop

Abstract

The GTP‐binding loop is an evolutionarily conserved structure found in the GTPase superfamily of proteins. The GTP‐binding loop enables GTPases to bind and hydrolyse GTP molecules and makes them excellent regulators of cellular processes.

Keywords: GTPase; GTP hydrolysis; guanine nucleotide; molecular switch; Ras

Figure 1.

Primary and secondary structures of human H‐Ras protein. The amino acid sequence of the Ras protein is shown in single‐letter code. The locations of α helices and β strands are indicated above the corresponding amino acid sequences. The locations of G loops are indicated below the corresponding amino acid sequences.

Figure 2.

Ras structures in three dimensions. (a) Crystal structure of Ras complexed with the GTP analogue guanosine‐5′‐(β,γ‐imido) triphosphate (GppNp) (Pai et al., ). The main chain is represented by ribbons with the five G loops in red, the six β strands in yellow, and the remaining portion in white. The side‐chains of selected amino acid residues in the G loops are depicted with orange space‐filled models. The bound GppNp is indicated (as ball and stick form) in blue, while the Mg2+ near the γ‐phosphate is indicated in green. (b) Crystal structure of Ras complexed with GDP (Milburn et al., ). The major differences of this structure from the Ras‐GppNp complex are the bound nucleotide GDP (in light green) and the conformational changes in the switch regions as indicated. The other regions are depicted as for the Ras‐GppNp structure in (a). (Figure courtesy of Timothy Mather.)

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Further Reading

Bourne HR, Sanders DA and McCormick F (1991) The GTPase superfamily: conserved structure and molecular mechanism. Nature 349: 117–126.

Sprang SR (1997) G protein mechanisms: insights from structural analysis. Annual Review of Biochemistry 66: 639.

Wittinghofer A (2000) The functioning of molecular switches in three dimensions. In: Hall A (ed.) GTPases, pp. 244–310. New York: Oxford University Press

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Li, Guangpu(Mar 2003) GTP‐binding Loop. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0003052]