Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
Nature. 2011 Dec 11;481(7380):219-23. doi: 10.1038/nature10691.
3-Methylcrotonyl-CoA carboxylase (MCC), a member of the biotin-dependent carboxylase superfamily, is essential for the metabolism of leucine, and deficient mutations in this enzyme are linked to methylcrotonylglycinuria (MCG) and other serious diseases in humans. MCC has strong sequence conservation with propionyl-CoA carboxylase (PCC), and their holoenzymes are both 750-kilodalton (kDa) α(6)β(6) dodecamers. Therefore the architecture of the MCC holoenzyme is expected to be highly similar to that of PCC. Here we report the crystal structures of the Pseudomonas aeruginosa MCC (PaMCC) holoenzyme, alone and in complex with coenzyme A. Surprisingly, the structures show that the architecture and overall shape of PaMCC are markedly different when compared to PCC. The α-subunits show trimeric association in the PaMCC holoenzyme, whereas they have no contacts with each other in PCC. Moreover, the positions of the two domains in the β-subunit of PaMCC are swapped relative to those in PCC. This structural information establishes a foundation for understanding the disease-causing mutations of MCC and provides new insights into the catalytic mechanism and evolution of biotin-dependent carboxylases. The large structural differences between MCC and PCC also have general implications for the relationship between sequence conservation and structural similarity.
3-甲基戊烯二酰辅酶 A 羧化酶（MCC）是生物素依赖的羧化酶超家族的成员，对亮氨酸的代谢至关重要，该酶的缺陷突变与甲基丙二酰辅酶 A 尿症（MCG）和人类的其他严重疾病有关。MCC 与丙酰辅酶 A 羧化酶（PCC）具有很强的序列保守性，它们的全酶都是 750 千道尔顿（kDa）的α（6）β（6）十二聚体。因此，MCC 全酶的结构预计与 PCC 高度相似。在这里，我们报道了铜绿假单胞菌 MCC（PaMCC）全酶的晶体结构，单独存在和与辅酶 A 复合的结构。令人惊讶的是，与 PCC 相比，结构显示 PaMCC 的结构和整体形状有明显的不同。α-亚基在 PaMCC 全酶中显示三聚体缔合，而在 PCC 中它们彼此没有接触。此外，PaMCC 的β-亚基的两个结构域的位置相对于 PCC 中的位置发生了交换。这些结构信息为理解 MCC 的致病突变奠定了基础，并为生物素依赖的羧化酶的催化机制和进化提供了新的见解。MCC 和 PCC 之间的大结构差异也对序列保守性和结构相似性之间的关系具有普遍意义。
