McPherson A, Brayer G, Morrison R
Biophys J. 1986 Jan;49(1):209-19. doi: 10.1016/S0006-3495(86)83635-9.
Crystals of a complex formed between ribonuclease A and d(pA)4 were grown and their structure determined by a combination of multiple isomorphous replacement (MIR) and molecular replacement techniques. The known structure of ribonuclease A in the correct orientation in the unit cell yielded a conventional crystallographic R factor of 0.32 at 2.8 A resolution when refined as a rigid body. Difference Fourier syntheses permitted determination of the disposition of the DNA in the unit cell. Refinement of both protein and DNA by constrained-restrained least squares procedures resulted in an R factor of 0.22 at 2.5 A resolution. The structure of the crystalline complex is comprised of four ordered oligomers of d(pA)4 associated with each molecule of RNAse. If the sites of interaction between protein and d(pA)4 fragments are mapped on the surface of the protein, they describe an essentially continuous path into and through the active site, across the surface of the enzyme and finally into the basic amino acid cluster on the opposite side of the protein.
核糖核酸酶A与d(pA)4形成的复合物晶体得以生长，并通过多重同晶置换（MIR）和分子置换技术相结合的方法确定了其结构。核糖核酸酶A在晶胞中正确取向的已知结构，在作为刚体进行精修时，于2.8 Å分辨率下得到了0.32的传统晶体学R因子。差值傅里叶合成使得能够确定DNA在晶胞中的位置。通过约束-限制最小二乘法对蛋白质和DNA进行精修，在2.5 Å分辨率下得到了0.22的R因子。晶体复合物的结构由与每个核糖核酸酶分子相关联的四个有序的d(pA)4寡聚体组成。如果将蛋白质与d(pA)4片段之间的相互作用位点映射到蛋白质表面，它们描绘出一条基本连续的路径，进入并穿过活性位点，跨越酶的表面，最终进入蛋白质另一侧的碱性氨基酸簇。
