Shen Yang, Chou Chi-Yuan, Chang Gu-Gang, Tong Liang
Department of Biological Sciences, Columbia University, New York, New York 10027.
Faculty of Life Sciences, National Yang-Ming University, Taipei 112, Taiwan.
Mol Cell. 2006 Jun 23;22(6):807-818. doi: 10.1016/j.molcel.2006.04.026.
Acetyl-coenzyme A carboxylases (ACCs) have crucial roles in fatty acid metabolism. The biotin carboxylase (BC) subunit of Escherichia coli ACC is believed to be active only as a dimer, although the crystal structure shows that the active site of each monomer is 25 A from the dimer interface. We report here biochemical, biophysical, and structural characterizations of BC carrying single-site mutations in the dimer interface. Our studies demonstrate that two of the mutants, R19E and E23R, are monomeric in solution but have only a 3-fold loss in catalytic activity. The crystal structures of the E23R and F363A mutants show that they can still form the correct dimer at high concentrations. Our data suggest that dimerization is not an absolute requirement for the catalytic activity of the E. coli BC subunit, and we propose a new model for the molecular mechanism of action for BC in multisubunit and multidomain ACCs.
乙酰辅酶A羧化酶（ACCs）在脂肪酸代谢中起着关键作用。尽管晶体结构显示每个单体的活性位点距离二聚体界面有25埃，但人们认为大肠杆菌ACC的生物素羧化酶（BC）亚基仅作为二聚体才具有活性。我们在此报告了在二聚体界面携带单点突变的BC的生化、生物物理和结构表征。我们的研究表明，其中两个突变体R19E和E23R在溶液中是单体，但催化活性仅损失了3倍。E23R和F363A突变体的晶体结构表明，它们在高浓度下仍能形成正确的二聚体。我们的数据表明，二聚化并非大肠杆菌BC亚基催化活性的绝对必要条件，并且我们提出了一个关于BC在多亚基和多结构域ACCs中作用分子机制的新模型。
