THE ALACOIL - A VERY TIGHT, ANTIPARALLEL COILED-COIL OF HELICES
THE ALACOIL - A VERY TIGHT, ANTIPARALLEL COILED-COIL OF HELICES
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DOI：
10.1002/pro.5560041102
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发表时间：
1995-11-01
期刊：
影响因子：
8
通讯作者：
RICHARDSON, DC
中科院分区：
文献类型：
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作者：
GERNERT, KM;SURLES, MC;RICHARDSON, DC
阿拉科伊尔（Alacoil）是一种反平行（而非通常的平行）的α-螺旋卷曲螺旋，每隔七个位置是丙氨酸（Ala）或另一种小残基，使得螺旋间距非常紧密（局部螺旋轴之间为7.5 - 8.5埃），通常超过四或五个螺旋圈。它存在两种不同的类型，其区别在于七肽重复序列的哪个位置被丙氨酸占据，以及两条螺旋主链上的最近点是对齐的还是错开半圈。对齐型，或称为ROP型，在七肽重复序列的“d”位置有丙氨酸，它位于螺旋接触的“尖端对尖端”侧，其中Cα - Cβ键指向彼此。更常见的错开型，或称为铁蛋白型的阿拉科伊尔，在七肽重复序列的“a”位置有丙氨酸（其中Cα - Cβ键背靠背，位于螺旋接触的“指关节接触”侧），并且两条螺旋的主链垂直错开半圈。在这两种形式中，连续的接触层中丙氨酸先是在一条螺旋上，然后在另一条螺旋上。阿拉科伊尔结构与纤维状蛋白质的卷曲螺旋或亮氨酸拉链有很多共同之处：两者都是α-螺旋卷曲螺旋，每七个残基重复一个关键氨基酸（亮氨酸或丙氨酸），并且中间有一个二级接触位置。然而，亮氨酸拉链是在对齐的平行螺旋之间（在二聚体中通常是相同的），而阿拉科伊尔是在反平行螺旋之间，通常是错开的，并且彼此靠得更近。因此，阿拉科伊尔可被视为一种“丙氨酸反拉链”。亮氨酸拉链中亮氨酸侧链有经典的“凸起嵌入凹槽”式堆积，在对面螺旋上形成由四个残基组成的菱形；对于阿拉科伊尔，螺旋靠得如此之近，以至于丙氨酸甲基必须选择菱形的一侧，并堆积在对面螺旋上由三个残基组成的三角形内。
我们以铁蛋白型阿拉科伊尔为基础，从头设计了一种由66个残基组成的卷曲螺旋发夹，称为“阿拉科伊林（Alacoilin）”。其序列为：cmS (P)̅ DQWDKE (A)̅ AQYDAH (A)̄ QE FEKK (S)̅ HRNng TPE (D)̅ QYRHM (A)̅ SQY QAM (A)̅ QK LKAI (A)̅ NQLKK Gsetcr（其中“a”七肽位置有下划线，非螺旋部分为小写），我们将对其进行生产，并测试其结构的稳定性和独特性。
The Alacoil is an antiparallel (rather than the usual parallel) coiled-coil of alpha-helices with Ala or another small residue in every seventh position, allowing a very close spacing of the helices (7.5-8.5 Angstrom between local helix axes), often over four or five helical turns. It occurs in two distinct types that differ by which position of the heptad repeat is occupied by Ala and by whether the closest points on the backbone of the two helices are aligned or are offset by half a turn. The aligned, or ROP, type has Ala in position ''d'' of the heptad repeat, which occupies the ''tip-to-tip'' side of the helix contact where the C alpha-C beta bonds point toward each other. The more common offset, or ferritin, type of Alacoil has Ala in position ''a'' of the heptad repeat (where the C alpha-C beta bonds lie back-to-back, on the ''knuckle-touch'' side of the heir contact), and the backbones of the two helices are offset vertically by half a turn. In both forms, successive layers of contact have the Ala first on one and then on the other helix.The Alacoil structure has much in common with the coiled-coils of fibrous proteins or leucine zippers: both are alpha-helical coiled-coils, with a critical amino acid repeated every seven residues (the Leu or the Ala) and a secondary contact position in between. However, Leu zippers are between aligned, parallel helices (often identical, in dimers), whereas Alacoils are between antiparallel helices, usually offset, and much closer together. The Alacoil, then, could be considered as an ''Ala anti-zipper.'' Leu zippers have a classic ''knobs-into-holes'' packing of the Leu side chain into a diamond of four residues on the opposite helix; for Alacoils, the helices are so close together that the Ala methyl group must choose one side of the diamond and pack inside a triangle of residues on the other helix.We have used the ferritin-type Alacoil as the basis for the de novo design of a 66-residue, coiled helix hairpin called ''Alacoilin.'' Its sequence is: cmS (P) under bar DQWDKE (A) under bar AQYDAH (A) over bar QE FEKK (S) under bar HRNng TPE (D) under bar QYRHM (A) under bar SQY QAM (A) under bar QK LKAI (A) under bar NQLKK Gsetcr (with ''a'' heptad positions underlined and nonhelical parts in lowercase), which we will produce and test for both stability and uniqueness of structure.