ORIGIN OF ANOMALOUS 13-C IR ENHANCEMENT IN ANTI-PARALLEL BETA-SHEET AGGREGATES

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。实验上，我们观察到反平行的b-折叠聚集体，如(Trp-Leu-*Leu-Leu)n，n=10-40，在13-C峰上表现出很强的增强作用。目的是从酰胺单元在一定程度上相互耦合的角度来理解这种异常增强。这是我们的模型所基于的。为了在线性红外光谱和二维红外光谱中获得结构-光谱关系，酰胺单元相互作用的知识是必不可少的。我们正在研究一个过渡电荷-电荷相互作用模型，其中为每个酰胺单元指定了一个过渡电荷实体。这个模型允许我们根据蛋白质数据库中提供的原子坐标计算几乎所有中等大小的二级基序的红外光谱。初步结果表明，导致13C峰增强的主要因素是以共价键或氢键形式存在的链间和链内最近邻的酰胺单元相互作用。这种增强依赖于聚集的长度和13-C标记的位置，这是可以预测的。我们还通过使用从头算正态模型计算来精炼最近邻单元的耦合强度，该模型计算同时考虑了贯穿空间和贯穿键的贡献。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Experimentally we have observed that the anti-parallel b-sheet aggregates e.g., (Trp-Leu-Leu-Leu-*Leu-Leu)n, n=10-40, show very strong enhancement in 13-C-peak. The objective is to understand this anomalous enhancement from the point of view of that the amide units are coupled to each other to certain extend. It is on which our model is based. The knowledge of amide unit interactions is essential in order to obtain structure-spectrum relationship in linear IR and 2D-IR as well. We are working on a transition charge-charge interaction model, in which a transition charge entity is designated for each amide unit. This model allows us to calculate the IR spectrum of almost all the mid-sized secondary motifs based on atomic coordinates that are available at Protein Data Bank. Preliminary results showed that the dominant factors responsible for the observed 13-C-peak enhancement are the inter-chain and intra-chain nearest neighbor amide unit interactions, which are covalently bonded or hydrogen bonded. The enhancement is dependent on the length of aggregation and on the 13-C-labeling positions, which can be predicted. We are also refining the coupling strengths of the nearest neighbor units, by using the ab initio normal model calculations that take into account of both the through-space and through-bond contributions.