STRUCTURE OF CYTOPLASMIC REGION OF LEUKOCYTE ANTIGEN RELATED (LAR) PROTEIN

细胞色素P450 cam的晶体结构 （S）-尼古丁测定为2.3
分辨率 （S）-尼古丁 作为细菌P450 cam的底物进行了广泛的研究 和人P450酶。 以前的动力学研究已经检查了 （S）-尼古丁与P450 cam的结合（Jones等人，1993，J. Am. Chem. Soc. 115，381-387.）。这表明（S）-尼古丁 在吡咯烷5'碳上的区域特异性单加氧，这意味着 该分子在活性部位与吡咯烷环 接近催化血红素铁。 相反，晶体结构 显示尼古丁分子的方向与 吡啶氮与血红素铁配位。 这是一致的 与紫外光谱研究，这表明形成一个低自旋 六配位铁对溶液中尼古丁与P450 cam结合的影响 （同上）。然而，吡咯烷5'碳约为8
从 晶体结构中的血红素铁，这表明 代表了一种非生产性的，尽管在能量上是有利的， 模式 这些发现将在第17届国际 生物学和分子生物学大会，1997年8月，弗朗西斯科， 并正在撰写出版（见下文）。 额外 研究现在正在检查配体的可能重新取向， 生产性装订。 这些包括检查（S）-尼古丁结合 在CO存在下，在还原条件下，转化为P450 cam。

The crystal structure of cytochrome P450cam complexed with (S)-nicotine has been determined at 2.3
resolution. (S)-nicotine has been extensively studied as a substrate of both bacterial P450cam and human P450 enzymes. Previous kinetic studies have examined (S)-nicotine binding to P450cam (Jones et al., 1993, J. Am. Chem. Soc. 115, 381-387.). These demonstrate that (S)-nicotine undergoes regiospecific monooxygenation at the pyrrolidine 5' carbon, implying that the molecule orients in the active site with the pyrrolidine ring close to the catalytic heme iron. In contrast, the crystal structure shows the nicotine molecule in a reversed orientation with the pyridine nitrogen coordinated with the heme iron. The is consistent with UV spectral studies, which indicate formation of a low-spin hexacoordinate iron upon nicotine binding to P450cam in solution (Ibid.). However, the pyrrolidine 5' carbon is approximately 8
from the heme iron in the crystal structure, indicating that this represents a nonproductive, though energetically favorable, binding mode. These findings will be presented at the 17th International Congress of Biology and Molecular Biology, August 1997, San FRancisco, and are being written up for publication (see below). Additional studies are now examining possible reorientation of the ligand for productive binding. These include examination of (S)-nicotine binding to P450cam in the presence of CO under reducing conditions.