Viëtor R J, Mazeau K, Lakin M, Pérez S
Ingéniérie Moléculaire, Institut National de la Recherche Agronomique, Rue de la Géraudière, BP 71627, 44316 Nantes Cédex, France.
Biopolymers. 2000 Oct 15;54(5):342-54. doi: 10.1002/1097-0282(20001015)54:5<342::AID-BIP50>3.0.CO;2-O.
The packing of beta-1,4-glucopyranose chains has been modeled to further elaborate the molecular structures of native cellulose microfibrils. A chain pairing procedure was implemented that evaluates the optimal interchain distance and energy for all possible settings of the two chains. Starting with a rigid model of an isolated chain, its interaction with a second chain was studied at various helix-axis translations and mutual rotational orientations while keeping the chains at van der Waals separation. For each setting, the sum of the van der Waals and hydrogen-bonding energy was calculated. No energy minimization was performed during the initial screening, but the energy and interchain distances were mapped to a three-dimensional grid, with evaluation of parallel settings of the cellulose chains. The emergence of several energy minima suggests that parallel chains of cellulose can be paired in a variety of stable orientations. A further analysis considered all possible parallel arrangements occurring between a cellulose chain pair and a further cellulose chain. Among all the low-energy three-chain models, only a few of them yield closely packed three-dimensional arrangements. From these, unit-cell dimensions as well as lattice symmetry were derived; interestingly two of them correspond closely to the observed allomorphs of crystalline native cellulose. The most favorable structural models were then optimized using a minicrystal procedure in conjunction with the MM3 force field. The two best crystal lattice predictions were for a triclinic (P(1)) and a monoclinic (P2(1)) arrangement with unit cell dimensions a = 0.63, b = 0.69, c = 1.036 nm, alpha = 113.0, beta = 121.1, gamma = 76.0 degrees, and a = 0.87, b = 0.75, c = 1.036 nm, gamma = 94.1 degrees, respectively. They correspond closely to the respective lattice symmetry and unit-cell dimensions that have been reported for cellulose Ialpha and cellulose Ibeta allomorphs. The suitability of the modeling protocol is endorsed by the agreement between the predicted and experimental unit-cell dimensions. The results provide pertinent information toward the construction of macromolecular models of microfibrils.
对β-1,4-吡喃葡萄糖链的堆积进行了建模，以进一步阐述天然纤维素微纤丝的分子结构。实施了一种链配对程序，该程序评估两条链的所有可能设置的最佳链间距离和能量。从孤立链的刚性模型开始，在保持链处于范德华间距的同时，研究了其在各种螺旋轴平移和相互旋转取向下与第二条链的相互作用。对于每种设置，计算范德华能和氢键能的总和。在初始筛选过程中未进行能量最小化，但将能量和链间距离映射到三维网格，并评估纤维素链的平行设置。几个能量最小值的出现表明纤维素的平行链可以以多种稳定取向配对。进一步的分析考虑了纤维素链对与另一条纤维素链之间所有可能的平行排列。在所有低能量三链模型中，只有少数几个产生紧密堆积的三维排列。由此得出晶胞尺寸以及晶格对称性；有趣的是，其中两个与观察到的结晶天然纤维素的同质多晶型物密切对应。然后使用微晶程序结合MM3力场对最有利的结构模型进行优化。两个最佳晶格预测分别是三斜晶系（P(1)）和单斜晶系（P2(1)）排列，晶胞尺寸分别为a = 0.63、b = 0.69、c = 1.036 nm，α = 113.0、β = 121.1、γ = 76.0度，以及a = 0.87、b = 0.75、c = 1.036 nm，γ = 94.1度。它们与已报道的纤维素Iα和纤维素Iβ同质多晶型物的相应晶格对称性和晶胞尺寸密切对应。预测的晶胞尺寸与实验值之间的一致性证实了建模方案的适用性。这些结果为构建微纤丝的大分子模型提供了相关信息。
