Sikorski Pawel, Hori Ritsuko, Wada Masahisa
Department of Physics, Norwegian University of Science and Technology, Trondheim NO-7491, Norway.
Biomacromolecules. 2009 May 11;10(5):1100-5. doi: 10.1021/bm801251e.
High resolution synchrotron X-ray fiber diffraction data recorded from crab tendon chitin have been used to describe the crystal structure of alpha-chitin. Crystal structures at 100 and 300 K have been solved using restrained crystallographic refinement against diffraction intensities measured from the fiber diffraction patterns. The unit cell contains two polymer chains in a 2(1) helix conformation and in the antiparallel orientation. The best agreement between predicated and observed X-ray diffraction intensities is obtained for a model that includes two distinctive conformations of C6-O6 hydroxymethl group. Those conformations are different from what is proposed in the generally accepted alpha-chitin crystal structure (J. Mol. Biol. 1978, 120, 167-181). Based on refined positions of the O6 atoms, a network of hydrogen bonds involving O6 is proposed. This network of hydrogen bonds can explain the main features of the polarized FTIR spectra of alpha-chitin and sheds some light on the origin of splitting of the amide I band observed on alpha-chitin IR spectra.
从蟹腱几丁质记录的高分辨率同步加速器X射线纤维衍射数据已用于描述α-几丁质的晶体结构。利用针对从纤维衍射图案测量的衍射强度进行的受限晶体学精修，解析了100 K和300 K时的晶体结构。晶胞包含两条呈2(1)螺旋构象且反平行取向的聚合物链。对于包含C6-O6羟甲基两种不同构象的模型，预测的和观察到的X射线衍射强度之间取得了最佳吻合。这些构象与普遍接受的α-几丁质晶体结构（《分子生物学杂志》1978年，第120卷，第167 - 181页）中所提出的不同。基于O6原子的精修位置，提出了一个涉及O6的氢键网络。这个氢键网络可以解释α-几丁质偏振傅里叶变换红外光谱的主要特征，并为α-几丁质红外光谱中观察到的酰胺I带分裂的起源提供一些线索。
