The crystal structure of a novel unmethylated form of C-phycocyanin, a possible connector between cores and rods in phycobilisomes
The crystal structure of a novel unmethylated form of C-phycocyanin, a possible connector between cores and rods in phycobilisomes
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DOI：
10.1074/jbc.m302838200
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发表时间：
2003-07-11
影响因子：
4.8
通讯作者：
Lerner, N
中科院分区：
文献类型：
--
作者：
Adir, N;Lerner, N
从嗜热蓝细菌Thermosynechcoccus vulcanus中分离出一种新的c-藻蓝蛋白组分，其最大吸收波长蓝移至612 nm（PC 612），并从别藻蓝蛋白中纯化得到。该晶体属于P6（3）空间群，晶胞尺寸为153埃× 153埃× 59埃，在不对称单元中具有单个（α）单体，导致溶剂含量为65%，并且折射率为2.7埃。PC612晶体结构已通过分子置换确定，并精确到20.9%的晶体学R因子（无R = 27.8%）。这种形式的晶体堆积表明，藻蓝蛋白的PC 612形式不结合成六聚体，并且其与晶胞中相邻三聚体的结合与先前确定的T正常形式的结构中发现的非常不同。vulcanus藻蓝蛋白，其在620 nm处吸收。对PC 612结构的分析表明，通常形成六聚体内两个三聚体之间界面的α亚基具有高度的柔性，如螺旋B、E和G部分中升高的B因子所示。对计算的电子密度省略图的检查表明，与迄今为止确定的藻胆蛋白的所有其他结构不同，Asnbeta（72）残基没有甲基化，这解释了其吸收光谱的蓝移。在这里提出的结果的基础上，我们建议，这种新形式的三聚体藻蓝蛋白可能构成一个特殊的次要组成部分的藻胆体，并可能形成藻蓝蛋白杆和别藻蓝蛋白核心之间的接触。
A novel fraction of c-phycocyanin from the thermophilic cyanobacterium Thermosynechcoccus vulcanus, with an absorption maxima blue-shifted to 612 nm (PC612), has been purified from allophycocyanin and crystallized. The crystals belong to the P6(3) space group with cell dimensions of 153 Angstrom x 153 Angstrom x 59 Angstrom with a single (alphabeta) monomer in the asymmetric unit, resulting in a solvent content of 65%, and diffract to 2.7 Angstrom. The PC612 crystal structure has been determined by molecular replacement and refined to a crystallographic R-factor of 20.9% (R-free = 27.8%). The crystal packing in this form shows that the PC612 form of phycocyanin does not associate into hexamers and that its association with adjacent trimers in the unit cell is very different from that found in a previously determined structure of the normal form of T. vulcanus phycocyanin, which absorbs at 620 nm. Analysis of the PC612 structure shows that the alpha subunits, which typically form the interface between two trimers within a hexamer, have a high degree of flexibility, as indicated by elevated B-factors in portions of helices B, E, and G. Examination of calculated electron density omit maps shows that unlike all other structures of phycobiliproteins determined so far, the Asnbeta(72) residue is not methylated, explaining the blue-shift in its absorption spectra. On the basis of the results presented here, we suggest that this new form of trimeric phycocyanin may constitute a special minor component of the phycobilisome and may form the contact between the phycocyanin rods and the allophycocyanin core.