Structural diversity of the active N-terminal kinase domain of p90 ribosomal S6 kinase 2.
The p90 ribosomal protein kinase 2 (RSK2) is a highly expressed Ser/Thr kinase activated by growth factors and is involved in cancer cell proliferation and tumor promoter-induced cell transformation. RSK2 possesses two non-identical kinase domains, and the structure of its N-terminal domain (NTD), which is responsible for phosphorylation of a variety of substrates, is unknown. The crystal structure of the NTD RSK2 was determined at 1.8 A resolution in complex with AMP-PNP. The N-terminal kinase domain adopted a unique active conformation showing a significant structural diversity of the kinase domain compared to other kinases. The NTD RSK2 possesses a three-stranded betaB-sheet inserted in the N-terminal lobe, resulting in displacement of the alphaC-helix and disruption of the Lys-Glu interaction, classifying the kinase conformation as inactive. The purified protein was phosphorylated at Ser227 in the T-activation loop and exhibited in vitro kinase activity. A key characteristic is the appearance of a new contact between Lys216 (betaB-sheet) and the beta-phosphate of AMP-PNP. Mutation of this lysine to alanine impaired both NTDs in vitro and full length RSK2 ex vivo activity, emphasizing the importance of this interaction. Even though the N-terminal lobe undergoes structural re-arrangement, it possesses an intact hydrophobic groove formed between the alphaC-helix, the beta4-strand, and the betaB-sheet junction, which is occupied by the N-terminal tail. The presence of a unique betaB-sheet insert in the N-lobe suggests a different type of activation mechanism for RSK2.
Malakhova
Margarita
M
Department of Cellular and Molecular Biology, The Hormel Institute, University of Minnesota, Austin, Minnesota, United States of America.
Kurinov
Igor
I
Liu
Kangdong
K
Zheng
Duo
D
D'Angelo
Igor
I
Shim
Jung-Hyun
JH
Steinman
Valerie
V
Bode
Ann M
AM
Dong
Zigang
Z
D000255:Adenosine Triphosphate / Q000737:chemistry*; D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000378:metabolism; D018698:Glutamic Acid / Q000737:chemistry; D008239:Lysine / Q000737:chemistry; D051379:Mice; D008968:Molecular Conformation; D009154:Mutation; D010766:Phosphorylation; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000737:chemistry* / Q000378:metabolism
D018698:Glutamic Acid; D000255:Adenosine Triphosphate; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C069330:ribosomal protein S6 kinase, 90kDa, polypeptide 3; D008239:Lysine