Kap95p binding induces the switch loops of RanGDP to adopt the GTP-bound conformation: implications for nuclear import complex assembly dynamics.
The asymmetric distribution of the nucleotide-bound state of Ran across the nuclear envelope is crucial for determining the directionality of nuclear transport. In the nucleus, Ran is primarily in the guanosine 5'-triphosphate (GTP)-bound state, whereas in the cytoplasm, Ran is primarily guanosine 5'-diphosphate (GDP)-bound. Conformational changes within the Ran switch I and switch II loops are thought to modulate its affinity for importin-beta. Here, we show that RanGDP and importin-beta form a stable complex with a micromolar dissociation constant. This complex can be dissociated by importin-beta binding partners such as importin-alpha. Surprisingly, the crystal structure of the Kap95p-RanGDP complex shows that Kap95p induces the switch I and II regions of RanGDP to adopt a conformation that resembles that of the GTP-bound form. The structure of the complex provides insights into the structural basis for the gradation of affinities regulating nuclear protein transport.
Forwood
Jade K
JK
School of Biomedical Sciences, Charles Sturt University, Wagga Wagga 2650, Australia. jforwood@csu.edu.au
Lonhienne
Thierry G
TG
Marfori
Mary
M
Robin
Gautier
G
Meng
Weining
W
Guncar
Gregor
G
Liu
Sai M
SM
Stewart
Murray
M
Carroll
Bernard J
BJ
Kobe
Bostjan
B
D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D006153:Guanosine Diphosphate / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D028961:beta Karyopherins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020931:ran GTP-Binding Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D046912:Multiprotein Complexes; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D028961:beta Karyopherins; D006153:Guanosine Diphosphate; D020931:ran GTP-Binding Protein