Severi Emmanuele, Müller Axel, Potts Jennifer R, Leech Andrew, Williamson David, Wilson Keith S, Thomas Gavin H
Department of Biology (Area 10), York Structural Biology Laboratory, University of York, York YO10 5YW, United Kingdom.
J Biol Chem. 2008 Feb 22;283(8):4841-9. doi: 10.1074/jbc.M707822200. Epub 2007 Dec 5.
The acquisition of host-derived sialic acid is an important virulence factor for some bacterial pathogens, but in vivo this sugar acid is sequestered in sialoconjugates as the alpha-anomer. In solution, however, sialic acid is present mainly as the beta-anomer, formed by a slow spontaneous mutarotation. We studied the Escherichia coli protein YjhT as a member of a family of uncharacterized proteins present in many sialic acid-utilizing pathogens. This protein is able to accelerate the equilibration of the alpha- and beta-anomers of the sialic acid N-acetylneuraminic acid, thus describing a novel sialic acid mutarotase activity. The structure of this periplasmic protein, solved to 1.5A resolution, reveals a dimeric 6-bladed unclosed beta-propeller, the first of a bacterial Kelch domain protein. Mutagenesis of conserved residues in YjhT demonstrated an important role for Glu-209 and Arg-215 in mutarotase activity. We also present data suggesting that the ability to utilize alpha-N-acetylneuraminic acid released from complex sialoconjugates in vivo provides a physiological advantage to bacteria containing YjhT.
获取宿主来源的唾液酸是一些细菌病原体的重要毒力因子，但在体内这种糖酸以α-异头物的形式被隔离在唾液酸结合物中。然而，在溶液中，唾液酸主要以β-异头物的形式存在，它是由缓慢的自发变旋形成的。我们研究了大肠杆菌蛋白YjhT，它是许多利用唾液酸的病原体中存在的一类未鉴定蛋白家族的成员。这种蛋白能够加速唾液酸N-乙酰神经氨酸α-和β-异头物的平衡，从而描述了一种新的唾液酸变旋酶活性。这种周质蛋白的结构解析到1.5埃分辨率，揭示了一个二聚体的6叶未封闭β-螺旋桨结构，这是细菌Kelch结构域蛋白中的第一个。YjhT中保守残基的诱变证明了Glu-209和Arg-215在变旋酶活性中的重要作用。我们还提供了数据表明，在体内利用从复杂唾液酸结合物中释放的α-N-乙酰神经氨酸的能力为含有YjhT的细菌提供了生理优势。
