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Three-dimensional structure of an oncogene protein: catalytic domain of human c-H-ras p21
A M de Vos1, L Tong, M V Milburn
1Department of Chemistry, University of California, Berkely 94720.
Abstract:
The crystal structure at 2.7 A resolution of the normal human c-H-ras oncogene protein lacking a flexible carboxyl-terminal 18 residue reveals that the protein consists of a six-stranded beta sheet, four alpha helices, and nine connecting loops. Four loops are involved in interactions with bound guanosine diphosphate: one with the phosphates, another with the ribose, and two with the guanine base. Most of the transforming proteins (in vivo and in vitro) have single amino acid substitutions at one of a few key positions in three of these four loops plus one additional loop. The biological functions of the remaining five loops and other exposed regions are at present unknown. However, one loop corresponds to the binding site for a neutralizing monoclonal antibody and another to a putative "effector region"; mutations in the latter region do not alter guanine nucleotide binding or guanosine triphosphatase activity but they do reduce the transforming activity of activated proteins. The data provide a structural basis for understanding the known biochemical properties of normal as well as activated ras oncogene proteins and indicate additional regions in the molecule that may possibly participate in other cellular functions.
Insights
Structural analysis of the human c-H-ras oncogene protein reveals key interactions with guanosine diphosphate. Mutations in specific loops affect transforming activity, offering insights into ras oncogene protein functions.
Area of Science:
- Molecular biology
- Structural biology
- Biochemistry
Background:
- The human c-H-ras oncogene protein plays a critical role in cellular signaling pathways.
- Understanding its structure is crucial for deciphering its function and its involvement in cancer.
Purpose of the Study:
- To determine the crystal structure of the normal human c-H-ras oncogene protein.
- To identify structural regions involved in guanosine diphosphate binding and protein function.
- To provide a structural basis for understanding normal and activated ras oncogene proteins.
Main Methods:
- X-ray crystallography at 2.7 A resolution.
- Analysis of protein structure, including beta sheets, alpha helices, and loops.
- Comparison of normal and transforming ras oncogene proteins.
Main Results:
- The protein structure comprises a six-stranded beta sheet, four alpha helices, and nine loops.
- Four loops are critical for binding guanosine diphosphate (GDP).
- Transforming ras proteins often have mutations in key loops affecting function, but not necessarily GDP binding.
Conclusions:
- The study provides a detailed structural map of the human c-H-ras oncogene protein.
- Identified structural features explain known biochemical properties of ras proteins.
- Suggests additional functional roles for unexplored regions of the protein.