Mazzarella L, Vitagliano L, Zagari A
Centro di Studio di Biocristallografia, Università di Napoli Federico II, Naples, Italy.
Proc Natl Acad Sci U S A. 1995 Apr 25;92(9):3799-803. doi: 10.1073/pnas.92.9.3799.
Bovine seminal ribonuclease (BS-RNase) is a homodimeric enzyme strictly homologous to the pancreatic ribonuclease (RNase A). Native BS-RNase is an equilibrium mixture of two distinct dimers differing in the interchange of the N-terminal segments and in their biological properties. The loop 16-22 plays a fundamental role on the relative stability of the two isomers. Both the primary and tertiary structures of the RNase A differ substantially from those of the seminal ribonuclease in the loop region 16-22. To analyze the possible stable conformations of this loop in both enzymes, structure predictions have been attempted, according to a procedure described by Palmer and Scheraga [Palmer, K. A. & Scheraga, H. A. (1992) J. Comput. Chem. 13, 329-350]. Results compare well with experimental x-ray structures and clarify the structural determinants that are responsible for the swapping of the N-terminal domains and for the peculiar properties of BS-RNase. Minimal modifications of RNase A sequence needed to form a stable swapped dimer are also predicted.
牛精核糖核酸酶（BS-RNase）是一种同二聚体酶，与胰腺核糖核酸酶（RNase A）严格同源。天然BS-RNase是两种不同二聚体的平衡混合物，这两种二聚体在N端片段的互换及其生物学特性方面存在差异。环16-22在两种异构体的相对稳定性中起重要作用。RNase A的一级和三级结构在环区域16-22中与精核糖核酸酶的结构有很大不同。为了分析该环在两种酶中可能的稳定构象，已根据Palmer和Scheraga描述的程序[Palmer, K. A. & Scheraga, H. A. (1992) J. Comput. Chem. 13, 329-350]尝试进行结构预测。结果与实验X射线结构吻合良好，并阐明了导致N端结构域互换以及BS-RNase特殊性质的结构决定因素。还预测了形成稳定的互换二聚体所需的RNase A序列的最小修饰。
