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Crystallographic Study of Wild‐type and Mg 2+ ‐free K‐Ras GTPase
Author(s) -
Parker Jillian,
Mattos Carla
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1116.3
Subject(s) - gtpase , gtp' , guanine nucleotide exchange factor , nucleotide , protein data bank (rcsb pdb) , chemistry , gtpase activating protein , effector , small gtpase , mutant , active site , guanine , g protein , guanosine diphosphate , signal transduction , biochemistry , guanosine triphosphate , enzyme , gene
The small GTPase Ras has been widely studied due to its relevance in cancer and other developmental disorders, termed RASopothies. When bound to GTP, Ras conveys signals to downstream effectors to control cellular signaling processes such as proliferation, differentiation, and apoptosis. Hydrolysis of GTP to GDP and inorganic phosphate (P i ) halts Ras signaling. This switching mechanism is tightly regulated by GEFs (guanine nucleotide exchange factors) and GAPs (GTPase activating proteins), where oncogenic mutations in Ras lead to uncontrolled Ras cell cycling and tumorigenesis. To date, structures of the most oncogenic isoform, K‐Ras, in its activated GTP‐bound form have been difficult to obtain, with only a couple of its mutants currently deposited in the Protein Data Bank (PDB). The first crystal structure of wild‐type K‐Ras bound to the GTP‐analogue GppCH 2 p has been obtained to 1.89Å resolution. This structure shows K‐Ras in the state 1 conformation, with switch I away from the active site without threonine 35 interacting with the Mg 2+ or nucleotide. Additionally, structures of active K‐Ras obtained from lower pH conditions show perturbed active site elements, the most striking of which is the absence of the canonical Mg 2+ ion in the nucleotide binding pocket. The Mg 2+ ‐less structures exhibit both local and long‐range alterations in residues located within conserved nucleotide‐binding motifs and involved in sensing the state of the nucleotide bound in the active site. Additionally, similarities are seen between Mg 2+ ‐less K‐Ras and nucleotide‐less Ras found in complex with Sos, the most common Ras GEF. These results shed light on why the active form of K‐Ras has been structurally difficult to characterize, as well as provide a structural basis for more focused targeting of the K‐Ras isoform. Support or Funding Information NSF MCB‐1244203