白色念珠菌形态转换的调控

白色念珠菌 (Ｃａｎｄｉｄａａｌｂｉｃａｎｓ)是一种常见的致病真菌 ,属于半知菌亚门芽孢菌纲隐球酵母科念珠菌属。在健康人体粘膜表面 ,如肠道、口腔 ,白色念珠菌通常不会引起疾病。但在免疫系统受到损害或抑制的人体中 ,比如化疗病人、器官移植病人或是艾滋病人中 ,白色念珠菌能够引起严重的白色念珠菌病 ,危及生命。许多因素可能与白色念珠菌的致病性有关 ,如菌体对寄主细胞的粘附能力、白色念珠菌产生的分泌性蛋白酶、菌落形态的转换以及细胞形态的转换等[1] 。1 .影响白色念珠菌形态转换的因素白色念珠菌能够以三种形态生长 ,即菌体形…     

白念珠菌菌丝发育的遗传调控

白念珠菌(Candidaalbicans)是人体内最重要的机会型致病真菌,能以酵母、假菌丝、菌丝等多种形态存在。白念珠菌的菌丝发育与它的致病性成正相关,这一过程由胞内多种信号转导途径所调控。现对控制白念珠菌菌丝发育的主要信号转导途径进行综述。     

Regulation of superoxide dismutase synthesis in Candida albicans

The synthesis of superoxide dismutase [SOD: EC 1.15.1.1] in response to various cultural conditions was examined in Candida albicans, an opportunistic yeast which causes candidiasis in immunosuppressed patients. SOD plays an important role in protecting cells from the oxidative damage of superoxide radicals. Maximum SOD activity was found after 72 hrs of yeast growth. The optimum pH and temperature for the SOD activity were 7 and 40 °, respectively. The major SOD activity was found in the cytosol fraction and the level of extracellular SOD was very low. The enzyme was stimulated to varying degrees by cholic acid, procaine and tocopherol. On the basis of inhibitor studies and other enzyme properties, the isolated enzyme from C. albicans is identified as copper and zinc superoxide dismutase. This revised version was published online in June 2006 with corrections to the Cover Date.     

Regulation of Rfa2 phosphorylation in response to genotoxic stress in Candida albicans

Successful pathogens must be able to swiftly respond to and repair DNA damages inflicted by the host defence. The replication protein A (RPA) complex plays multiple roles in DNA damage response and is regulated by phosphorylation. However, the regulators of RPA phosphorylation remain unclear. Here, we investigated Rfa2 phosphorylation in the pathogenic fungus Candida albicans. Rfa2, a RFA subunit, is phosphorylated when DNA replication is inhibited by hydroxyurea and dephosphorylated during the recovery. By screening a phosphatase mutant library, we found that Pph3 associates with different regulatory subunits to differentially control Rfa2 dephosphorylation in stressed and unstressed cells. Site‐directed mutagenesis revealed T11, S18, S29, and S30 being critical for Rfa2 phosphorylation in response to genotoxic insult. We obtained evidence that the genome integrity checkpoint kinase Mec1 and the cyclin‐dependent kinase Clb2–Cdc28 mediate Rfa2 phosphorylation. Although cells expressing either a phosphomimetic or a non‐phosphorylatable version of Rfa2 had defects, the latter exhibited greater sensitivity to genotoxic challenge, failure to repair DNA damages and to deactivate Rad53‐mediated checkpoint pathways in a dosage‐dependent manner. These mutants were also less virulent in mice. Our results provide important new insights into the regulatory mechanism and biological significance of Rfa2 phosphorylation in C. albicans.     

Regulation and solubilization of Candida albicans chitin synthetase.

A cytoplasmic component which inhibited the activation of chitin synthetase was studied in the dimorphic fungus Candida albicans. The inhibitor was found to be heat stable and trypsin sensitive and was only effective when incubated with a vacuolar protease, an activator of chitin synthetase, before the activation of chitin synthetase. In addition, the particulate chitin synthetase from the yeast form of C. albicans was solubilized by a sodium cholate-digitonin extraction and subsequently was purified approximately 30-fold by Sepharose column chromatography and Amicon XM 100 filtration. Activity of the soluble enzyme was increased by the addition of trypsin or phosphatidyl serine. The molecular weight of the enzyme was estimated to be 400,000.     

Regulation of chitin synthesis during germ-tube formation in Candida albicans

The synthesis of chitin during germ-tube formation in Candida albicans may be regulated by the first and last steps in the chitin pathway: namely l-glutamine-d-fructose-6-phosphate aminotransferase and chitin synthase. Induction of germ-tube formation with either glucose and glutamine or serum was accompanied by a 4-fold increase in the specific activity of the aminotransferase. Chitin synthase in C. albicans is synthesized as a proenzyme. N-acetyl glucosamine increased the enzymic activity of the activated enzyme 3-fold and the enzyme exhibited positive co-operativity with the substrate, UDP-N-acetylglucosamine. Although chitin synthase was inhibited by polyoxin D (K _i =1.2M) this antibiotic did not affect germination. During germ-tube formation the total chitin synthase activity increased 1.4-fold and the expressed activity (in vivo activated proenzyme) increased 5-fold. These results could account for the reported 5-fold increase in chitin content observed during the yeast to mycelial transformation.Non-Standard Abbreviations GlcNac N-acetyl glucosamine - UDP-GlcNac UDP-N-acetyl glucosamine - PMSF phenylmethylsulphonylfluoride     

白念珠菌高铁还原酶职FRP1基因的功能

白念珠菌((Candida albicans)获得铁的能力影响细胞的生长和毒力,高铁还原酶是白念珠菌高亲和铁吸收系统的重要组成部分.[目的]构建高铁还原酶FRP1(Ferric reductase protein)基因缺失突变株,对FRP1基因功能进行初步研究.[方法]使用Northem杂交的方法分析FRP1基因在缺铁和富铁条件下的表达.利用PCR介导的基因敲除技术构建frp1缺失突变株,并且对野生型和缺失突变株在细胞高铁还原酶活性以及缺铁条件下的生长情况进行比较分析.[结果]缺铁条件可以诱导FRP1基因的表达.frp1缺失突变株不能在铁缺陷的固体培养基上生长.[结论]FRP1蛋白可能是白念珠菌在缺铁条件下起主要作用的高铁还原酶.     

Function of Candida albicans adhesin Hwp1 in biofilm formation

Hwp1 is a well-characterized Candida albicans cell surface protein, expressed only on hyphae, that mediates tight binding to oral epithelial cells. Prior studies indicate that HWP1 expression is dependent upon Bcr1, a key regulator of biofilm formation. Here we test the hypothesis that Hwp1 is required for biofilm formation. In an in vitro model, the hwp1/hwp1 mutant produces a thin biofilm that lacks much of the hyphal mass found in the hwp1/HWP1 reconstituted strain. In a biofilm cell retention assay, we find that the hwp1/hwp1 mutant is defective in retention of nonadherent bcr1/bcr1 mutant cells. In an in vivo rat venous catheter model, the hwp1/hwp1 mutant has a severe biofilm defect, yielding only yeast microcolonies in the catheter lumen. These properties of the hwp1/hwp1 mutant are consistent with its role as a hypha-specific adhesin and indicate that it is required for normal biofilm formation. Overexpression of HWP1 in a bcr1/bcr1 mutant background improves adherence in the in vivo catheter model. This finding provides additional support for the model that Hwp1 is critical for biofilm adhesion. Hwp1 is the first cell surface protein known to be required for C. albicans biofilm formation in vivo and is thus an excellent therapeutic target.     

Antimorphogenic effects of 2-deoxy-D-glucose in Candida albicans

Abstract 2-Deoxy- d -glucose (dGlc) is able to inhibit both N -acetyl-hexosamine-induced chlamydosporogenesis and N -acetyl-glucosamine- or proline-induced germ-tube formation in Candida albicans . This inhibition is exerted also at dGlc concentrations which do not affect growth in the yeast form and do not reduce either the uptake or the incorporation of N-acetyl- d -glucosamine (GlcNAc) into yeast or hyphal cell material. Inhibition of germtube formation by dGlc does not occur in serum and is fully reversed by glucose. It is suggested that dGlc acts as a potent antimorphogenic effector in C. albicans .     

白念珠菌肌醇多磷酸激酶Kcs1的功能

【目的】鉴定白念珠菌肌醇多磷酸激酶Kcs1蛋白,并探索Kcs1在该病原菌细胞自噬、菌丝发育及致病过程中的功能。【方法】采用二步PCR介导的同源重组方法,构建白念珠菌KCS1基因缺失菌株kcs1Δ/Δ及回补菌株KCS1c;采用氮饥饿敏感性测定及GFP-Atg8自噬报告系统,测定KCS1缺失对白念珠菌自噬过程的影响;采用菌丝诱导培养,测定KCS1缺失对白念珠菌菌丝发育能力的影响;采用巨噬细胞模型及小鼠系统性感染模型,分析KCS1缺失对白念珠菌感染宿主能力的影响。【结果】KCS1缺失造成白念珠菌氮饥饿耐受能力降低,氮饥饿条件下自噬相关蛋白Atg8的降解及转运水平下降,菌丝发育变缓,对巨噬细胞耐受及损伤能力减弱,但不影响菌株的小鼠系统性感染能力。【结论】白念珠菌肌醇多磷酸激酶Kcs1在细胞自噬、菌丝发育、与巨噬细胞相互作用等方面发挥重要作用。