Crump M P, Crosby J, Dempsey C E, Parkinson J A, Murray M, Hopwood D A, Simpson T J
School of Chemistry, University of Bristol Molecular Recognition Centre, University of Bristol, U.K.
Biochemistry. 1997 May 20;36(20):6000-8. doi: 10.1021/bi970006+.
The solution structure of the actinorhodin acyl carrier protein (act apo-ACP) from the polyketide synthase (PKS) of Streptomyces coelicolor A3(2) has been determined using 1H NMR spectroscopy, representing the first polyketide synthase component for which detailed structural information has been obtained. Twenty-four structures were generated by simulated annealing, employing 699 distance restraints and 94 dihedral angle restraints. The structure is composed, principally, of three major helices (1, 2, and 4), a shorter helix (3) and a large loop region separating helices 1 and 2. The structure is well-defined, except for a portion of the loop region (residues 18-29), the N-terminus (1-4), and a short stretch (57-61) in the loop connecting helices 2 and 3. The RMS distribution of the 24 structures about the average structure is 1.47 A for backbone atoms, 1.84 A for all heavy atoms (residues 5-86), and 1.01 A for backbone atoms over the helical regions (5-18, 41-86). The tertiary fold of act apo-ACP shows a strong structural homology with Escherichia coli fatty acid synthase (FAS) ACP, though some structural differences exist. First, there is no evidence that act apo-ACP is conformationally averaged between two or more states as observed in E. coli FAS ACP. Second, act apo-ACP shows a disordered N-terminus (residues 1-4) and a longer flexible loop (19-41 with 19-29 disordered) as opposed to E. coli FAS ACP where the N-terminal helix starts at residue 3 and the loop region is three amino acids shorter (16-35). Most importantly, however, although the act apo-ACP structure contains a hydrophobic core, there are in addition a number of buried hydrophilic groups, principally Arg72 and Asn79, both of which are 100% conserved in the PKS ACPs and not the FAS ACPs and may therefore play a role in stabilizing the growing polyketide chain. The structure-function relationship of act ACP is discussed in the light of these structural data and recent genetic advances in the field.
利用核磁共振波谱法已确定了天蓝色链霉菌A3(2)聚酮合酶（PKS）中放线紫红素酰基载体蛋白（放线菌脱辅基酰基载体蛋白，act apo-ACP）的溶液结构，这是首个获得详细结构信息的聚酮合酶组分。通过模拟退火生成了24个结构，采用了699个距离约束和94个二面角约束。该结构主要由三个主要螺旋（1、2和4）、一个较短的螺旋（3）以及分隔螺旋1和2的一个大环区域组成。除了环区域的一部分（残基18 - 29）、N端（1 - 4）以及连接螺旋2和3的环中的一小段（57 - 61）外，该结构定义明确。24个结构围绕平均结构的均方根分布，主链原子为1.47 Å，所有重原子（残基5 - 86）为1.84 Å，螺旋区域（5 - 18、41 - 86）的主链原子为1.01 Å。act apo-ACP的三级结构与大肠杆菌脂肪酸合酶（FAS）ACP表现出很强的结构同源性，不过也存在一些结构差异。首先，没有证据表明act apo-ACP像在大肠杆菌FAS ACP中观察到的那样在两种或更多种状态之间构象平均化。其次，act apo-ACP的N端（残基1 - 4）无序，环更长且更灵活（19 - 41，其中19 - 29无序），而大肠杆菌FAS ACP的N端螺旋从残基3开始，环区域短三个氨基酸（16 - 35）。然而，最重要的是，尽管act apo-ACP结构包含一个疏水核心，但此外还有一些埋藏的亲水基团，主要是精氨酸72和天冬酰胺79，这两个基团在PKS ACP中100%保守，而在FAS ACP中则不然，因此可能在稳定生长的聚酮链中发挥作用。根据这些结构数据和该领域最近的遗传学进展，讨论了act ACP的结构 - 功能关系。
