Iengar Prathima, Joshi N V, Balaram Padmanabhan
Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India.
Structure. 2006 Mar;14(3):529-42. doi: 10.1016/j.str.2005.11.021.
beta helix proteins are characterized by a repetitive fold, in which the repeating unit is a beta-helical coil formed by three strand segments linked by three loop segments. Using a data set of left- and right-handed beta helix proteins, we have examined conformational features at equivalent positions in successive coils. This has provided insights into the conformational rules that the proteins employ to fold into beta helices. Left-handed beta helices attain their equilateral prism fold by incorporating "corners" with the conformational sequence P(II)-P(II)-alpha(L)-P(II), which imposes sequence restrictions, resulting in the first and third P(II) residues often being G and a small, uncharged residue (V, A, S, T, C), respectively. Right-handed beta helices feature mid-sized loops (4, 5, or 6 residues) of conserved conformation, but not of conserved sequence; they also display an alpha-helical residue at the C-terminal end of L2 loops. Backbone conformational parameters (phi,psi) that permit the formation of continuous, loopless beta helices (Perutz nanotubes) have also been investigated.
β螺旋蛋白的特征是具有重复折叠结构，其中重复单元是由三个链段通过三个环段连接形成的β螺旋线圈。利用一组左旋和右旋β螺旋蛋白数据集，我们研究了连续线圈中等价位置的构象特征。这为蛋白质折叠成β螺旋所采用的构象规则提供了见解。左旋β螺旋通过结合构象序列为P(II)-P(II)-α(L)-P(II)的“转角”来实现其等边棱柱折叠，这对序列有一定限制，导致第一个和第三个P(II)残基通常分别为甘氨酸和一个小的不带电荷残基（缬氨酸、丙氨酸、丝氨酸、苏氨酸、半胱氨酸）。右旋β螺旋具有保守构象但序列不保守的中等大小环（4、5或6个残基）；它们在L2环的C末端还显示有一个α螺旋残基。还研究了允许形成连续、无环β螺旋（佩鲁茨纳米管）的主链构象参数（φ，ψ）。
