The radical S-adenosylmethionine (SAM) superfamily currently comprises more than 2800 proteins with the amino acid sequence motif CxxxCxxC unaccompanied by a fourth conserved cysteine. The charcteristic three-cysteine motif nucleates a [4Fe-4S] cluster, which binds SAM as a ligand to the unique Fe not ligated to a cysteine residue. The members participate in more than 40 distinct biochemical transformations, and most members have not been biochemically characterized. A handful of the members of this superfamily have been purified and at least partially characterized. Significant mechanistic and structural information is available for lysine 2,3-aminomutase, pyruvate formate-lyase, coproporphyrinogen III oxidase, and MoaA required for molybdopterin biosynthesis. Biochemical information is available for spore photoproduct lyase, anaerobic ribonucleotide reductase activation subunit, lipoyl synthase, and MiaB involved in methylthiolation of isopentenyladenine-37 in tRNA. The radical SAM enzymes biochemically characterized to date have in common the cleavage of the [4Fe-4S](1 +) -SAM complex to [4Fe-4S](2 +)-Met and the 5' -deoxyadenosyl radical, which abstracts a hydrogen atom from the substrate to initiate a radical mechanism.

中文翻译：

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自由基SAM超家族。

自由基S-腺苷甲硫氨酸（SAM）超家族目前包含2800多种蛋白，其氨基酸序列基序CxxxCxxC不伴有第四个保守的半胱氨酸。具有特征的三半胱氨酸基序使[4Fe-4S]簇成核，该簇将SAM作为配体与未与半胱氨酸残基连接的独特Fe结合。成员参与40多个不同的生化转化，并且大多数成员尚未进行生化鉴定。该超家族中的少数成员已被纯化并至少部分特征化。有关赖氨酸2，3-氨基变位酶，丙酮酸甲酸裂解酶，原卟啉原III氧化酶和钼蝶呤生物合成所需的MoaA的重要机制和结构信息可用。可提供孢子光产物裂解酶的生化信息，厌氧核糖核苷酸还原酶激活亚基，脂酰合酶和MiaB参与tRNA中异戊烯腺嘌呤37的甲基硫醇化。迄今为止，已生化表征的自由基SAM酶共有[4Fe-4S]（1 +）-SAM复合物裂解为[4Fe-4S]（2 +）-Met和5'-脱氧腺苷自由基的裂解，氢原子从底物上引发自由基机理。