Biosynthesis of the corrin ring of vitamin B12 requires the action of six S-adenosyl-L-methionine (AdoMet) dependent transmethylases, closely related in sequence. The first X-ray structure of one of these, cobalt-precorrin-4 transmethylase, CbiF, from Bacillus megaterium has been determined to a resolution of 2.4 Ã
. CbiF contains two α/β domains forming a trough in which S-adenosyl-L-homocysteine (AdoHcy) binds. The location of AdoHcy and a number of conserved residues, helps define the precorrin binding site. A second crystal form determined at 3.1 Ã
resolution highlights the flexibility of two loops around this site. CbiF employs a unique mode of AdoHcy binding and represents a new class of transmethylase.
维生素 B12 的珊瑚酸环的
生物合成需要六种
S-腺苷-L-蛋氨酸(AdoMet)依赖性转甲基酶的作用,它们在序列上密切相关。我们首次测定了其中一种转甲基酶的 X 射线结构,即巨型芽孢杆菌中的
钴-4 转甲基酶 CbiF,其分辨率为 2.4 μm。CbiF 包含两个 α/β 结构域,形成一个 S-
腺苷-
L-高半胱氨酸(AdoHcy)结合的槽。AdoHcy 的位置和一些保守残基有助于确定
前胡素的结合位点。以 3.1 Ã 分辨率测定的第二种晶体形式突出显示了该位点周围两个环的灵活性。CbiF 采用了一种独特的 AdoHcy 结合模式,代表了一类新的跨甲基酶。