An open conformation of switch I revealed by the crystal structure of a Mg2+-free form of RHOA complexed with GDP. Implications for the GDP/GTP exchange mechanism.
Mg(2+) ions are essential for guanosine triphosphatase (GTPase) activity and play key roles in guanine nucleotide binding and preserving the structural integrity of GTP-binding proteins. We determined the crystal structure of a small GTPase RHOA complexed with GDP in the absence of Mg(2+) at 2.0-A resolution. Elimination of a Mg(2+) ion induces significant conformational changes in the switch I region that opens up the nucleotide-binding site. Similar structural changes have been observed in the switch regions of Ha-Ras bound to its guanine nucleotide exchange factor, Sos. This RHOA-GDP structure reveals an important regulatory role for Mg(2+) and suggests that guanine nucleotide exchange factor may utilize this feature of switch I to produce an open conformation in GDP/GTP exchange.
Shimizu
T
T
Division of Strucural Biology and Signal Transduction, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan.
Ihara
K
K
Maesaki
R
R
Kuroda
S
S
Kaibuchi
K
K
Hakoshima
T
T
D001665:Binding Sites; D018360:Crystallography, X-Ray; D006153:Guanosine Diphosphate / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism*; D007091:Image Processing, Computer-Assisted; D008274:Magnesium / Q000032:analysis*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D020742:rhoA GTP-Binding Protein; D008274:Magnesium