STRUCTURE OF BETA-SHEETS - ORIGIN OF THE RIGHT-HANDED TWIST AND OF THE INCREASED STABILITY OF ANTIPARALLEL OVER PARALLEL SHEETS
STRUCTURE OF BETA-SHEETS - ORIGIN OF THE RIGHT-HANDED TWIST AND OF THE INCREASED STABILITY OF ANTIPARALLEL OVER PARALLEL SHEETS
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DOI：
10.1016/0022-2836(82)90163-2
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发表时间：
1982-01-01
影响因子：
5.6
通讯作者：
SCHERAGA, HA
中科院分区：
文献类型：
--
作者：
CHOU, KC;POTTLE, M;SCHERAGA, HA
2和3链的反平行和平行的β-折叠的能量被最小化。这两条链被认为是等价的。在每种情况下，检查分别由4个和8个L-丙氨酸残基组成的链，这些链具有CH3CO-和-NHCH3端基。对被约束为具有规则结构(即，相同的.vphi)的链进行了这两种计算。和.PSI。每个残基的二面角)和放松了正则性约束的链。正如在蛋白质中观察到的那样，所有计算的最小能量β-片断都有右旋扭曲。与右旋α-螺旋的情况一样，链内非键相互作用能在迫使L氨基酸残基的β-片断采用右旋扭曲中起关键作用。有利于右旋扭曲的非键能贡献是涉及CβH3基团的Mamy小的成对原子间相互作用的结果。聚甘氨酸-β--缺少C.beta.H3侧链的片层不会扭曲。聚L-丙氨酸薄片的扭转随着每条链上残基数量的增加而减小，这与观察到的结果一致。在从单链到2链反平行结构的过程中，4-残基链的扭转度略有增加(由于链间非键相互作用，也涉及CβH3基团)，但在从2链到3链结构的过程中略有降低。观察到的蛋白质结构中的β-片层有时比这里计算的结构中的那些有更大的扭曲。这可能是由于观察到的片层中氨基酸序列和氢键模式的不规则性，或者是由于蛋白质中的远程相互作用。平行β-层的最小能量比相应的反平行β-层的能量要高得多，这表明平行β-层本质上不太稳定。这一关于两种β-折叠的发现与基于对蛋白质中观察到的β-折叠进行分析的建议一致。反平行和平行β-CHEET之间的能量差异是由于链的堆积更紧密，以及反平行结构中的肽偶极子有更有利的排列。计算得到的反平行结构中的氢键几何构型与Arnott等人提出的非常接近。(1967)用于聚L丙氨酸的β-形式。
The energies of 2 and 3-chain antiparallel and parallel .beta.-sheets were minimized. The chains were considered to be equivalent. In each case, chains consisting of 4 and of 8 L-alanine residues, respectively, with CH3CO- and -NHCH3 end groups were examined. Computations were carried out both for chains constrained to have a regular structure (i.e. the same .vphi. and .psi. dihedral angles for each residue) and for chains in which the regularity constraint was relaxed. All computed minimum-energy .beta.-sheets had a right-handed twist, as observed in proteins. As in the case of right-handed .alpha.-helices, it is the intrastrand non-bonded interaction energy that plays the key role in forcing .beta.-sheets of L-amino acid residues to adopt a right-handed twist. The non-bonded energy contribution favoring the right-handed twist is the result of mamy small pairwise interatomic interactions involving the C.beta.H3 groups. Polyglycine .beta.-sheets, lacking the C.beta.H3 side-chains, are not twisted. The twist of the poly-L-alanine sheet diminishes as the number of residues per chain increases in agreement with observations. The twist of the 4-residue chain increases somewhat (because of interstrand non-bonded interactions, also involving the C.beta.H3 groups) in going from a single chain to a 2-chain antiparallel structure, but then decreases slightly in going from a 2-chain to a 3-chain structure. .beta.-Sheets in observed protein structures sometimes have a larger twist than those in the structures computed here. This may be due to irregularities in amino acid sequence and in H-bonding patterns in the observed sheets, or to long-range interactions in proteins. The minimized energies of parallel .beta.-sheets are considerably higher than those of the corresponding antiparallel .beta.-cheets, indicating that parallel .beta.-sheets are intrinsically less stable. This finding about the 2 kinds of .beta.-sheets agrees with suggestions based on analyses of .beta.-sheets observed in proteins. The energy difference between antiparallel and parallel .beta.-cheets is due to closer packing of the chains and a more favorable alignment of the peptide dipoles in the antiparallel structures. The H-bond geometry in the computed antiparallel structures is very close to that proposed by Arnott et al. (1967) for the .beta.-form for poly-L-alanine.