Monaco R, Chen J M, Chung D, Brandt-Rauf P, Pincus M R
Department of Chemistry, New York University, New York 10003, USA.
J Protein Chem. 1995 Aug;14(6):457-66. doi: 10.1007/BF01888140.
The ras-oncogene-encoded p21 protein becomes oncogenic if amino acid substitutions occur at critical positions in the polypeptide chain. The most commonly found oncogenic forms contain Val in place of Gly 12 or Leu in place of Gln 61. To determine the effects of these substitutions on the three-dimensional structure of the whole p21 protein, we have performed molecular dynamics calculations on each of these three proteins bound to GDP and magnesium ion to compute the average structures of each of the three forms. Comparisons of the computed average structures shows that both oncogenic forms with Val 12 and Leu 61 differ substantially in structure from that of the wild type (containing Gly 12 and Gln 61) in discrete regions: residues 10-16, 32-47, 55-74, 85-89, 100-110, and 119-134. All of these regions occur in exposed loops, and several of them have already been found to be involved in the cellular functioning of the p21 protein. These regions have also previously been identified as the most flexible domains of the wild-type protein and have been bound to be the same ones that differ in conformation between transforming and nontransforming p21 mutant proteins neither of which binds nucleotide. The two oncogenic forms have similar conformations in their carboxyl-terminal domains, but differ in conformation at residues 32-47 and 55-74. The former region is known to be involved in the interaction with at least three downstream effector target proteins. Thus, differences in structure between the two oncogenic proteins may reflect different relative affinities of each oncogenic protein for each of these effector targets. The latter region, 55-74, is known to be a highly mobile segment of the protein. The results strongly suggest that critical oncogenic amino acid substitutions in the p21 protein cause changes in the structures of vital domains of this protein.
如果在多肽链的关键位置发生氨基酸替换，由原癌基因ras编码的p21蛋白就会变成致癌蛋白。最常见的致癌形式是，第12位的甘氨酸被缬氨酸取代，或者第61位的谷氨酰胺被亮氨酸取代。为了确定这些替换对整个p21蛋白三维结构的影响，我们对这三种与GDP和镁离子结合的蛋白分别进行了分子动力学计算，以计算出这三种形式各自的平均结构。计算得到的平均结构比较结果表明，第12位为缬氨酸和第61位为亮氨酸的这两种致癌形式在离散区域的结构与野生型（第12位为甘氨酸、第61位为谷氨酰胺）有很大不同：残基10 - 16、32 - 47、55 - 74、85 - 89、100 - 110和119 - 134。所有这些区域都出现在暴露的环中，其中有几个区域已被发现与p21蛋白的细胞功能有关。这些区域先前也被确定为野生型蛋白最灵活的结构域，并且被认为与转化型和非转化型p21突变蛋白（两者均不结合核苷酸）之间构象不同的区域相同。这两种致癌形式在其羧基末端结构域具有相似的构象，但在残基32 - 47和55 - 74处的构象不同。已知前一个区域参与与至少三种下游效应靶蛋白的相互作用。因此，这两种致癌蛋白之间的结构差异可能反映了每种致癌蛋白对这些效应靶蛋白各自不同的相对亲和力。后一个区域，即55 - 74，是该蛋白高度可移动的片段。结果强烈表明，p21蛋白中关键的致癌氨基酸替换会导致该蛋白重要结构域的结构发生变化。
