Tang Aihua, Caballero Armando R, Bierdeman Michael A, Marquart Mary E, Foster Timothy J, Monk Ian R, O'Callaghan Richard J
Department of Microbiology and Immunology, University of Mississippi Medical Center, Jackson, MS 39216, USA.
Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College, Dublin 2, D02 PN40, Ireland.
Pathogens. 2019 Jan 1;8(1):2. doi: 10.3390/pathogens8010002.
is a major cause of corneal infections that can cause reduced vision, even blindness. Secreted toxins cause tissue damage and inflammation resulting in scars that lead to vision loss. Identifying tissue damaging proteins is a prerequisite to limiting these harmful reactions. The present study characterized a previously unrecognized toxin. This secreted toxin was purified from strain Newman , the N-terminal sequence determined, the gene cloned, and the purified recombinant protein was tested in the rabbit cornea. The virulence of a toxin deletion mutant was compared to its parent and the mutant after gene restoration (rescue strain). The toxin (23 kDa) had an N-terminal sequence matching the Newman superantigen-like protein SSL1. An SSL1 homodimer (46 kDa) had proteolytic activity as demonstrated by zymography and cleavage of a synthetic substrate, collagens, and cytokines (IL-17A, IFN-γ, and IL-8); the protease was susceptible to serine protease inhibitors. As compared to the parent and rescue strains, the mutant had significantly reduced virulence, but not reduced bacterial growth, in vivo. The ocular isolates tested had the gene, with allele type 2 being the predominant type. SSL1 is a protease with corneal virulence and activity on host defense and structural proteins.
是角膜感染的主要原因，可导致视力下降甚至失明。分泌的毒素会造成组织损伤和炎症，进而形成疤痕，导致视力丧失。识别造成组织损伤的蛋白质是限制这些有害反应的前提条件。本研究对一种此前未被识别的毒素进行了表征。这种分泌毒素是从纽曼菌株中纯化得到的，测定了其N端序列，克隆了基因，并在兔角膜中对纯化的重组蛋白进行了测试。将毒素缺失突变体的毒力与其亲本以及基因恢复后的突变体（拯救菌株）进行了比较。该毒素（23 kDa）的N端序列与纽曼超抗原样蛋白SSL1匹配。通过酶谱分析以及对合成底物、胶原蛋白和细胞因子（IL-17A、IFN-γ和IL-8）的切割证明，SSL1同二聚体（46 kDa）具有蛋白水解活性；该蛋白酶对丝氨酸蛋白酶抑制剂敏感。与亲本菌株和拯救菌株相比，该突变体在体内的毒力显著降低，但细菌生长未受影响。所测试的眼部分离株含有该基因，等位基因类型2为主要类型。SSL1是一种对角膜具有毒力且对宿主防御和结构蛋白有活性的蛋白酶。
