Programa de Pós Graduação em Biologia Celular e Molecular, Centro de Biotecnologia, Universidade Federal do Rio Grande, Porto Alegre, Brazil.
FEBS J. 2015 Apr;282(8):1406-18. doi: 10.1111/febs.13229. Epub 2015 Mar 2.
Ureases (EC 3.5.1.5) are Ni(2+) -dependent metalloenzymes produced by plants, fungi and bacteria that hydrolyze urea to produce ammonia and CO2 . The insertion of nickel atoms into the apo-urease is better characterized in bacteria, and requires at least three accessory proteins: UreD, UreF, and UreG. Our group has demonstrated that ureases possess ureolytic activity-independent biological properties that could contribute to the pathogenicity of urease-producing microorganisms. The presence of urease in pathogenic bacteria strongly correlates with pathogenesis in some human diseases. Some medically important fungi also produce urease, including Cryptococcus neoformans and Cryptococcus gattii. C. gattii is an etiological agent of cryptococcosis, most often affecting immunocompetent individuals. The cryptococcal urease might play an important role in pathogenesis. It has been proposed that ammonia produced via urease action might damage the host endothelium, which would enable yeast transmigration towards the central nervous system. To analyze the role of urease as a virulence factor in C. gattii, we constructed knockout mutants for the structural urease-coding gene URE1 and for genes that code the accessory proteins Ure4 and Ure6. All knockout mutants showed reduced multiplication within macrophages. In intranasally infected mice, the ure1Δ (lacking urease protein) and ure4Δ (enzymatically inactive apo-urease) mutants caused reduced blood burdens and a delayed time of death, whereas the ure6Δ (enzymatically inactive apo-urease) mutant showed time and dose dependency with regard to fungal burden. Our results suggest that C. gattii urease plays an important role in virulence, in part possibly through enzyme activity-independent mechanism(s).
脲酶（EC 3.5.1.5）是一种依赖镍（Ni(2+)）的金属酶，由植物、真菌和细菌产生，能将尿素水解为氨和二氧化碳。镍原子插入脱辅基脲酶的过程在细菌中得到了更好的描述，需要至少三种辅助蛋白：UreD、UreF 和 UreG。我们的研究小组已经证明，脲酶具有与尿素酶活性无关的生物学特性，这些特性可能有助于产生脲酶的微生物的致病性。在一些人类疾病中，致病性细菌中存在脲酶与发病机制密切相关。一些医学上重要的真菌也产生脲酶，包括新型隐球菌和格特隐球菌。格特隐球菌是隐球菌病的病原体，最常影响免疫功能正常的个体。隐球菌脲酶可能在发病机制中发挥重要作用。有人提出，脲酶作用产生的氨可能会损害宿主内皮细胞，从而使酵母向中枢神经系统迁移。为了分析脲酶作为格特隐球菌毒力因子的作用，我们构建了结构脲酶编码基因 URE1 及其辅助蛋白编码基因 Ure4 和 Ure6 的敲除突变体。所有敲除突变体在巨噬细胞内的增殖能力均降低。在鼻腔感染的小鼠中，ure1Δ（缺乏脲酶蛋白）和 ure4Δ（无酶活性的脱辅基脲酶）突变体导致血液负荷降低和死亡时间延迟，而 ure6Δ（无酶活性的脱辅基脲酶）突变体则表现出与真菌负荷有关的时间和剂量依赖性。我们的结果表明，格特隐球菌脲酶在毒力中起着重要作用，部分可能通过非酶活性机制。
