Srinivasan N, White H E, Emsley J, Wood S P, Pepys M B, Blundell T L
Laboratory of Molecular Biology, Birkbeck College, University of London, UK.
Structure. 1994 Nov 15;2(11):1017-27. doi: 10.1016/S0969-2126(94)00105-7.
Pentraxins are a family of plasma proteins characterized by their pentameric assembly and calcium-dependent ligand binding. The recent determination of the crystal structure for a member of this family, human serum amyloid P component (SAP), provides a basis for the comparative analysis of the pentraxin family.
We have compared the sequences, tertiary structures and quaternary arrangements of SAP with human C-reactive protein (CRP), Syrian hamster SAP (HSAP) and Limulus polyphemus CRP (LIM). These proteins can adopt a beta-jelly roll topology and a hydrophobic core similar to that seen in SAP. Only minor differences are observed in the positions of residues involved in coordinating calcium ions.
Calcium-mediated ligand binding by CRP, HSAP and LIM is similar to that defined by the crystal structure of SAP, but sequence differences in the hydrophobic pocket explain the differential ligand specificities exhibited by the homologous proteins. Differences elsewhere, including insertions and deletions, account for the different (hexameric) quaternary structure of LIM.
五聚体蛋白是一类血浆蛋白家族，其特征在于它们的五聚体组装和钙依赖性配体结合。最近对该家族成员之一人血清淀粉样蛋白P成分（SAP）的晶体结构测定，为五聚体蛋白家族的比较分析提供了基础。
我们比较了人C反应蛋白（CRP）、叙利亚仓鼠SAP（HSAP）和鲎CRP（LIM）与SAP的序列、三级结构和四级排列。这些蛋白可以采用类似于SAP中所见的β-果冻卷拓扑结构和疏水核心。在参与钙离子配位的残基位置仅观察到微小差异。
CRP、HSAP和LIM通过钙介导的配体结合类似于由SAP晶体结构所定义的结合，但疏水口袋中的序列差异解释了同源蛋白所表现出的不同配体特异性。其他地方的差异，包括插入和缺失，解释了LIM不同的（六聚体）四级结构。
