Crystallographic Study of a Quinoprotein Electron Transfer System: Methylamine Dehydrogenase

生物大分子之间的电子转移通常发生在瞬时复合物中，其中参与的氧化还原中心和介入蛋白质被最佳地配置为促进和调节中心之间的电子流。只有少数这样的复合物已经结晶。甲胺脱氢酶（MADH）和amicyanin，两者一起和细胞色素，形成两个结构特征的生理电子转移复合物;芳香胺脱氢酶（AADH）与天青蛋白的复合物包括第三个。MADH和AADH以及醌血红素蛋白胺脱氢酶（QHNDH）催化伯胺的氧化脱氨基。所有三种酶都含有氧化还原辅因子色氨酸醌（TRQ），这是一种含有两个醌氧原子的色氨酸侧链。TRQ与MADH和AADH中的另一个色氨酸或QHNDH中的半胱氨酸交联。该项目的目的是进行以下结构研究：（1）具有改变的氧化还原性质的amicyanin突变体，单独和与MADH复合，（2）AADH/天青蛋白复合物的氧化还原变体和配体结合形式，以及（3）TRQ及其与QHNDH中半胱氨酸交联的作用和生物起源。这些结果将有助于识别对生物电子转移调节重要的结构特征，包括伴侣识别，驱动力调节，重组能量和门控。TRQ生物发生的研究是重要的，因为在生物学中普遍存在的后修饰的氨基酸侧链，其作用和生物发生机制知之甚少。 拟议活动产生的更广泛影响将包括促进国内和国际本科生研究培训。将继续努力使当地大学生参与结构研究，意大利的电子转移复合物单晶光谱研究将为国外学生提供培训环境。该研究还将通过与日本和意大利的科学家及其学生的国际伙伴关系加强研究基础设施。

Electron transfer between biological macromolecules usually occurs within a transient complex in which the participating redox centers and the intervening protein are optimally configured to promote and regulate electron flow between the centers. Only a few such complexes have been crystallized. Methylamine dehydrogenase (MADH) and amicyanin, both together and with a cytochrome, form two structurally characterized physiological electron transfer complexes; the complex of aromatic amine dehydrogenase (AADH) with azurin comprises a third. MADH and AADH, as well as quinohemoprotein amine dehydrogenase (QHNDH), catalyze the oxidative deamination of primary amines. All three enzymes contain the redox cofactor tryptophylquinone (TRQ), a tryptophan side chain containing two quinone oxygen atoms. TRQ is crosslinked to another tryptophan in MADH and AADH or to a cysteine in QHNDH. The aims of this project are to carry out structural studies of (1) amicyanin mutants with altered redox properties, alone and in complex with MADH, (2) redox variants and ligand-bound forms of the AADH/azurin complex and (3) the roles and biogenesis of TRQ and its crosslink to cysteine in QHNDH. The results will help identify structural features important for modulation of biological electron transfer, including partner recognition, regulation of driving force, reorganization energy and gating. The studies of TRQ biogenesis are important because of the ubiquity in biology of posttranslationally modified amino acid side chains whose roles and biogenic mechanisms are poorly understood. The broader impacts resulting from the proposed activity will include the promotion of undergraduate training in research both nationally and internationally. Efforts to involve local undergraduates in the structural studies will continue and single crystal spectroscopic studies of electron transfer complexes in Italy will provide a training environment for students abroad. The research will also enhance research infrastructure through international partnerships with scientists and their students in Japan and Italy.