STRUCTURE OF HUMAN LACTOFERRIN - CRYSTALLOGRAPHIC STRUCTURE-ANALYSIS AND REFINEMENT AT 2.8-A RESOLUTION
STRUCTURE OF HUMAN LACTOFERRIN - CRYSTALLOGRAPHIC STRUCTURE-ANALYSIS AND REFINEMENT AT 2.8-A RESOLUTION
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DOI：
10.1016/0022-2836(89)90602-5
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发表时间：
1989-10-20
影响因子：
5.6
通讯作者：
BAKER, EN
中科院分区：
文献类型：
--
作者：
ANDERSON, BF;BAKER, HM;BAKER, EN
人乳铁蛋白的晶体结构在2.8 . ang下得到了细化。(1 .ANG。= 0.1 nm)分辨率。起始模型来源于3.2 . ang。图相采用多次同构置换用溶剂压平。在精化过程中的重建大量使用了这些实验阶段，并结合了部分模型计算的阶段。目前的模型包括691个氨基酸残基中的681个，2个Fe3+和2个CO32-，在10到2.8 . ang之间的17266个观测反射的R因子为0.206。分辨率，与标准键长的均方根偏差为0.03 ang…由于精化的结果，在氨基酸序列中进行了两次单残基插入和一次13残基缺失，并阐明了二级结构和三级相互作用的细节。分子的两个裂片，分别代表n端和c端，具有非常相似的折叠，重叠后的均方根偏差为1.32 . ang。330个c α中的285个。原子;唯一的主要区别在于表面回路。每个叶被细分为两个不同的。α。/。β。域名，一个基于六链混合。β。另一种是五股混合β。-薄片，铁位点在域间裂隙中。在目前的分辨率下，这两个铁点似乎是相同的。每个铁原子与四个蛋白质配体配位，2个Tyr， 1个Asp， 1个His和特定的CO32-，其似乎以双齿模式与铁结合。阴离子占据铁和蛋白质上两个带正电荷的基团（精氨酸侧链、N端和螺旋5）之间的一个口袋，可能在铁结合之前中和这个正电荷。一个大的内部空腔，在Arg侧链之外，可能是更大的阴离子结合作为CO32-替代品的原因。在铁位点的另一侧，靠近区域间交叉链的残基可能提供二次阴离子结合位点，这可能解释了与血清转铁蛋白相比，乳铁蛋白结合铁的酸稳定性更强。还讨论了结构域间和叶间相互作用、带电侧链的作用、重原子结合位点以及与不同金属结合有关的金属位点的构建。
The structure of human lactoferrin has been refined crystallographically at 2.8 .ANG. (1 .ANG. = 0.1 nm) resolution using restrained least squares methods. The starting model was derived from a 3.2 .ANG. map phased by multiple isomorphous replacement with solvent flattening. Rebuilding during refinement made extensive use of these experimental phases, in combination with phases calculated from the partial model. The present model, which includes 681 of the 691 amino acid residues, two Fe3+, and two CO32-, gives an R factor of 0.206 for 17,266 observed reflections between 10 and 2.8 .ANG. resolution, with a root-mean-square deviation from standard bond lengths of 0.03 .ANG.. As a result of the refinement, two single-residue insertions and one 13-residue deletion have been made in the amino acid sequence, and details of the secondary structure and tertiary interactions have been clarified. The two lobes of the molecule, representing the N-terminal and C-terminal halves, have very similar folding, with a root-mean-square deviation, after superposition, of 1.32 .ANG. for 285 out of 330 C.alpha. atoms; the only major differences being in surface loops. Each lobe is subdivided into two dissimilar .alpha./.beta. domains, one based on a six-stranded mixed .beta.-sheet, the other on a five-stranded mixed .beta.-sheet, with the iron site in the interdomain cleft. The two iron sites appear identical at the present resolution. Each iron atom is coordinated to four protein ligands, 2 Tyr, 1 Asp, 1 His, and the specific CO32-, which appears to bind to iron in a bidentate mode. The anion occupies a pocket between the iron and two positively charged groups on the protein, an arginine side-chain and the N terminus and helix 5, and may serve to neutralize this positive charge prior to iron binding. A large internal cavity, beyond the Arg side-chain, may account for the binding of larger anions as substitutes for CO32-. Residues on the other side of the iron site, near the interdomain crossover strands could provide secondary anion binding sites, and may explain the greater acid-stability of iron binding by lactoferrin, compared with serum transferrin. Interdomain and interlobe interactions, the roles of charged side-chains, heavy-atom binding sites, and the construction of the metal site in relation to the binding of different metals are also discussed.