University of Wroclaw, Faculty of Chemistry, Department of Crystallography, 14 F. Joliot-Curie, Wroclaw, 50383, Poland.
Hirszfeld Institute of Immunology and Experimental Therapy, Polish Academy of Sciences, 12 R. Weigl, Wroclaw, 53114, Poland.
Sci Rep. 2017 May 22;7(1):2223. doi: 10.1038/s41598-017-02451-3.
Tail tubular protein A (TTPA) is a structural tail protein of Klebsiella pneumoniae bacteriophage KP32, and is responsible for adhering the bacteriophage to host cells. For the first time, we found that TTPA also exhibits lytic activity towards capsular exopolysaccharide (EPS) of the multiresistant clinical strain of Klebsiella pneumoniae, PCM2713, and thus should be regarded as a dual-function macromolecule that exhibits both structural and enzymatic actions. Here, we present our crystallographic and enzymatic studies of TTPA. TTPA was crystallized and X-ray diffraction data were collected to a resolution of 1.9 Å. In the crystal, TTPA molecules were found to adopt a tetrameric structure with α-helical domains on one side and β-strands and loops on the other. The novel crystal structure of TTPA resembles those of the bacteriophage T7 tail protein gp11 and gp4 of bacteriophage P22, but TTPA contains an additional antiparallel β-sheet carrying a lectin-like domain that could be responsible for EPS binding. The enzymatic activity of TTPA may reflect the presence of a peptidoglycan hydrolase domain in the α-helical region (amino acid residues 126 to 173). These novel results provide new insights into the enzymatic mechanism through which TTPA acts on polysaccharides.
尾管蛋白 A（TTPA）是肺炎克雷伯氏菌噬菌体 KP32 的结构尾部蛋白，负责将噬菌体附着在宿主细胞上。我们首次发现，TTPA 还对多耐药临床株肺炎克雷伯氏菌 PCM2713 的荚膜胞外多糖（EPS）具有裂解活性，因此应被视为一种具有结构和酶促双重功能的大分子。在此，我们介绍了 TTPA 的晶体学和酶学研究。TTPA 被结晶并收集到 1.9Å 的分辨率的 X 射线衍射数据。在晶体中，TTPA 分子被发现采用四聚体结构，一侧有α-螺旋结构域，另一侧有β-链和环。TTPA 的新颖晶体结构类似于噬菌体 T7 尾部蛋白 gp11 和噬菌体 P22 的 gp4，但 TTPA 包含一个额外的携带凝集素样结构域的反平行β-片层，该结构域可能负责 EPS 结合。TTPA 的酶活性可能反映了在α-螺旋区域（氨基酸残基 126 到 173）中存在肽聚糖水解酶结构域。这些新的结果为 TTPA 作用于多糖的酶促机制提供了新的见解。
