Computational and experimental studies on positive ions derived from peptides

蛋白质组学在很大程度上依赖于质谱法来确定蛋白质的至少一小段中的氨基酸序列。 通常，蛋白质被酶（胰蛋白酶）分解，一些产物肽中氨基酸残基的序列通过它们在质谱中的片段化来确定。 肽片段化的机制仍不十分清楚。 我们正在以几种方式解决这个问题。 我们正在研究质子化肽（通常的目标）片段的机制的细节;这通常需要研究更简单的肽的构建模块，氨基酸。 我们还将碎片化研究扩展到两种不同类型的离子，（1）通过破坏铜离子/肽复合物在电喷雾质谱中形成的肽的自由基阳离子，以及（2）连接到更高电荷离子（如La 3+离子）的肽复合物。 这两类离子将给出关于肽的不同类型的信息，并将有助于澄清从质子化肽研究中获得的测序信息中的模糊性。在所有这些实验工作中，密度泛函理论计算将用于确定中间体的结构，并确定它们相互转化的障碍。

Proteomics relies very heavily on mass spectrometry to determine the sequence of amino acids in at least a short segment of a protein. Usually the protein is broken down by an enzyme (trypsin) and the sequences of the amino acid residues in some of the product peptides are determined by their fragmentation in a mass spectrometry. The mechanisms by which peptides fragment are still not very well understood. We are addressing this problem in several ways. We are examining details of the mechanisms by which protonated peptides (the usual target) fragment; this frequently necessitates looking at the even simpler building blocks of peptides, the amino acids. We are also expanding fragmentation studies into two different classes of ions, (1) radical cations of peptides formed in electrospray mass spectrometry by breaking copper ion / peptide complexes, and (2) complexes of peptides attached to more highly charged ions like a La3+ ion. These two classes of ions will give different types of information about the peptides and will help clear up ambiguities in the sequencing information obtained from the protnated peptide studies. Throughout all this experimental work Density Functional Theory calculations will be used to determine the structures of intermediates and to determine the barriers to their interconversion.