Max-Planck-Institut für Strahlenchemie, Postfach 101365, D-45413, Mülheim an der Ruhr, Germany.
Photosynth Res. 1994 Jul;41(1):225-33. doi: 10.1007/BF02184163.
The supramolecular structure of methyl (3(1) R)-BChlided aggregation has been explored by molecular modelling in order to elucidate the unusual structure of the BChl rods in the chlorosomal antennae of green bacteria. The aggregate construction progressed from a BChlide monomer in 5c coordination which was stepwise combined to form trimeric, pentameric and decameric chlorin stacks, all incorporating Mg····O-H as a basic interaction element which links two chlorins between the 3(1)-hydroxyl oxygen and the Mg. Up to the level of the trimer, the structures were optimized by both a semiempirical quantum chemical method (PM3) and a force field method, while larger structures were only modelled by the force field (MM+). Strong interactions were found by extended stacking of chlorins which are in van der Waals contact. Extended hydrogen bonding networks upon stack pairing brought about by OH····O=C bonds (bond length ca. 2.2Å, angle 139-153°) between appropriately situated chlorin pairs and by electrostatic interactions lead to very large energy stabilizations. The structural features of a modelled 40mer BChl aggregate are in full accord with all spectroscopic and low-resolution structural information on the in-vitro and chlorosomal BChl aggregates. Most important, from the rotation angle between stacks of ca. 16° and the stack-to-stack distance of 7.6 Å a tubular structure can be extrapolated to form on further extension of the aggregate. It has a predicted diameter of about 5.4 nm (Mg-Mg distance), i.e. very similar to that found for the rod elements in the chlorosomes ofChloroflexus.
为了阐明绿色细菌的菌绿体天线中叶绿素棒的不寻常结构，通过分子建模研究了甲基（3(1) R）-BChlide 聚集物的超分子结构。聚合体结构从 5c 配位的叶绿素单体开始，逐步组合形成三聚体、五聚体和十聚体叶绿素堆叠，所有堆叠都包含 Mg····O-H 作为基本相互作用元素，将两个叶绿素之间的 3(1)-羟基氧和 Mg 连接起来。在三聚体水平上，结构通过半经验量子化学方法（PM3）和力场方法进行了优化，而较大的结构仅通过力场（MM+）进行建模。通过范德华接触的叶绿素的扩展堆叠发现了强相互作用。通过 OH····O=C 键（键长约 2.2Å，角度 139-153°）和静电相互作用在堆叠对之间形成扩展氢键网络，导致非常大的能量稳定化。模拟的 40 聚体 BChl 聚集体的结构特征与体外和菌绿体 BChl 聚集体的所有光谱和低分辨率结构信息完全一致。最重要的是，从堆叠之间约 16°的旋转角度和 7.6Å 的堆叠间距离，可以推断出管状结构可以进一步延伸形成聚合体。它的预测直径约为 5.4nm（Mg-Mg 距离），与菌绿体中的棒状元素非常相似。
