溶菌酶及其分子改造研究进展

溶菌酶是一种优异的天然抗菌蛋白,可以成为抗生素和化学防腐剂的有效替代物,解决日益严峻的细菌耐药性问题和抗生素残留、化学防腐剂超标等食品安全问题。因此,深入研究并构建具有新型广谱杀菌能力的溶菌酶,对食品、医药、畜牧等行业的发展有着重要意义。对溶菌酶的分类、胞壁质酶活性和非酶活性杀菌性质以及蛋白质改造方法,特别是利用现代生物技术对溶菌酶进行抗菌活性增强、抗菌谱拓展的研究进行了综述和展望。     

动物源溶菌酶研究进展

动物源溶菌酶是一种动物体内广泛存在的酶类,它可以水解细菌细胞壁肽聚糖中的β-1,4糖苷键,具有消化分解细菌、抑制外源微生物生长、增强机体免疫力的作用.目前溶菌酶已被用作研究蛋白功能、性质以及分子进化的模型.首先介绍了溶菌酶及其分子的晶体结构,溶菌酶基因及其蛋白研究进展,其次介绍了动物源溶菌酶的功能,包括溶菌酶生物学功能和重组蛋白功能活性,重点介绍了溶菌酶基因在转基因工程中的应用研究,最后对动物源溶菌酶研究进行了展望.研究动物源溶菌酶对于基础科学,并应用其转变成现实生产力具有重要的指导意义.     

细菌细胞壁的结构

了解细菌细胞壁的结构,对于研究细菌的分类、遗传、及噬菌体的感染,对于解释抗生素和溶菌酶等对细菌的作用,以及革兰氏染色的机理等,都是很重要的。本文拟对细菌细胞壁的结构作一简述。     

一种溶菌酶样蛋白对肺炎链球菌毒力及荚膜多糖合成的影响

摘要：【目的】为了研究肺炎链球菌（Streptococcus pneumoniae, S.pn）的一种假想的溶菌酶样蛋白在细菌生物学性状及其致病中的作用。【方法】利用长臂同源PCR对该基因进行敲出,并同时构建带有拯救质粒的缺失菌株,观察D39野生菌、缺失菌与带有拯救质粒的缺失菌株在相关生物学性状及其致病力改变,从而鉴定这种假想溶菌酶样蛋白的功能。【结果】缺失菌与野生菌相比,细菌生长减缓,毒力下降,荚膜多糖合成明显减少。而将拯救质粒转入缺失菌株后,该溶菌酶样蛋白的mRNA表达水平较野生菌高,其毒力及荚膜合成     

罗非鱼3种C型溶菌酶重组蛋白的制备及与几种鱼虾溶菌酶溶菌谱的比较

应用基因工程技术制备了3种奥利亚罗非鱼C型溶菌酶的重组蛋白,并应用比浊法比较了它们与草鱼C型溶菌酶、G型溶菌酶和斑节对虾C型溶菌酶重组蛋白对无乳链球菌、嗜水气单胞菌等8种细菌的溶菌作用.研究发现,6种重组溶菌酶对这8种菌均具有溶菌活性,但是溶菌活力强弱不一.其中罗非鱼C3溶菌酶对革兰氏阳性菌无乳链球菌的溶菌作用最强,草鱼C型与G型溶菌酶次之;所有重组溶菌酶对革兰氏阴性菌铜绿假单胞菌均具较强的溶菌活性.与斑节对虾C型溶菌酶、草鱼C型与G型溶菌酶相比,罗非鱼的C型溶菌酶对嗜水气单胞菌具有较强的溶菌作用,且以C1的溶菌活性最强.本研究结果可为选择具较强溶菌活力的溶菌酶应用于养殖生产提供依据,并可为应用转基因技术培育抗病品种提供靶基因.     

人源溶菌酶结构与功能的研究进展

人溶菌酶是一类人体内天然存在的能够溶解细菌细胞壁的碱性蛋白的总称。其作用特征是能够裂解肽聚糖中的N-乙酰氨基葡萄糖与N-乙酰氨基甲酸之间的β-(1,4)-糖苷键。人溶菌酶具有抗菌、抗炎、抗病毒和增强免疫力等多种特性,因此在国内外市场上应用广泛。本文就人溶菌酶的结构特点、表达部位、功能表达以及应用情况进行综述。     

溶菌酶的研究进展

溶菌酶普遍存在于动物、植物和微生物中。溶菌酶是一种小分子碱性蛋白,长期以来一直被作为一种“模型”体系．用于研究蛋白质的空间构象、酶动力学及其与分子进化、分子免疫间的关系。介绍了溶菌酶的来源、结构、性质、作用机制。并对近年来其在食品工业、医学和酶工程中的应用进行了综述;分析了溶菌酶应用中存在的主要问题,并对其应用前景进行了展望。     

T4溶菌酶在多型汉逊酵母中的表达及抑菌活性测定

溶菌酶是一类对多种细菌都具有明显杀菌效果的蛋白质.本研究将T4溶菌酶基因构建到毕赤酵母表达载体pPIC9K中,以汉逊酵母A16来源的rDNA序列作为同源重组序列,在毕赤酵母甘油醛-3-磷酸脱氢酶启动子（pGAP）的调控下,使T4溶菌酶在汉逊酵母A16中以组成型方式稳定高效表达.在37℃,pH6.0,摇瓶发酵培养72h后,表达量达到0.49g/L.结果表明,汉逊酵母能够识别源自毕赤酵母的甘油醛-3-磷酸脱氢酶启动子和醇氧化酶终止子序列,而且rDNA作为同源重组序列可以产生多拷贝的汉逊酵母重组子.对重组蛋白进行了N端测序、质谱及SDS-PAGE检测,发现重组蛋白N端与T4溶菌酶N端氨基酸序列一致,分子量大小约为18.7kD,与预计分子量大小相符.重组T4溶菌酶对革兰氏阳性和阴性细菌都具有抑菌活性和溶壁活性.非变性SDS-PAGE（无DTT）检测发现,重组T4溶菌酶形成了分子内二硫键和少量分子间二硫键,这种不正确的二硫键可能导致重组T4溶菌酶损失部分抗菌活性.     

本期重点推介

正溶菌酶通过破坏细菌细胞壁的完整结构,最终导致细菌裂解死亡,在昆虫的体液免疫中扮演着重要角色。小菜蛾Plutella xylostella是危害十字花科蔬菜的世界性害虫之一。为了明确小菜蛾溶菌酶的分子特性和功能,福建师范大学生命科学学院宁燕夏和杨梅等利用RACE技术克隆小菜蛾溶菌酶基因Pxlys,利用原核表达系统表达和纯化获得Pxlys重组蛋白,利用牛津杯法检测Pxlys重组蛋白对3种革兰氏阳性细菌和4种革兰氏阴性细菌的抑菌活性,并利用扫描电子显微镜观察Pxlys重组蛋白对停滞棒杆菌Corynebacterium stationis和大肠杆菌Escherichia coli的溶菌特征,结果显示Pxlys对革兰氏阳性细菌和革兰氏阴性细菌均有抑菌活性,其中对革兰氏阳性细菌的抑菌活性更强,且溶菌特征不同(pp.781-789)。     

野生东亚钳蝎消化道可培养细菌的分离鉴定、耐药性及产消化酶活性

目的 分离东亚钳蝎消化道中的可培养细菌,并研究其产消化酶活性和耐药性,探讨消化道细菌对东亚钳蝎消化食物的影响。 方法 野生东亚钳蝎采用传统细菌分离培养方法分离其消化道内可培养细菌,利用16S rRNA序列进行细菌的分子鉴定;利用平板透明圈法测定可培养细菌产淀粉酶、蛋白酶、脂肪酶和纤维素酶等消化酶的活性;采用药敏纸片扩散法进行消化道可培养细菌的药敏试验。 结果 在东亚钳蝎消化道中共分离到4个属10种细菌,其中芽胞杆菌属7种,分别为蛋白水解芽胞杆菌、解淀粉芽胞杆菌、巨大芽胞杆菌、枯草芽胞杆菌、蜡样芽胞杆菌、婴儿芽胞杆菌和长形赖氨酸芽胞杆菌;葡萄球菌属、纤维微菌属和短波单胞菌属各1株,分别为松鼠葡萄球菌、纤维化纤维微细菌和泡囊短波单胞菌。对10种细菌的产消化酶活性分析表明,8种细菌有产消化酶活性,占细菌总数的80%;5种细菌有产蛋白酶活性,分别为蛋白水解芽胞杆菌、枯草芽胞杆菌、蜡样芽胞杆菌、松鼠葡萄球菌和纤维化纤维微细菌;7种细菌有产淀粉酶活性,分别为蛋白水解芽胞杆菌、解淀粉芽胞杆菌、巨大芽胞杆菌、枯草芽胞杆菌、蜡样芽胞杆菌、松鼠葡萄球菌和婴儿芽胞杆菌;未筛选到产纤维素酶和脂肪酶活性的细菌;蛋白水解芽胞杆菌、枯草芽胞杆菌、蜡样芽胞杆菌和松鼠葡萄球菌可同时产2种消化酶。在药敏试验中,8种细菌对多粘菌素B耐药,5种细菌对四环素耐药,3种细菌对万古霉素耐药。 结论 东亚钳蝎消化道中可培养细菌的组成相对单一,多数细菌有分泌淀粉酶和蛋白酶的功能,说明东亚钳蝎消化道中的细菌可能有协助其进行食物消化的功能。消化道细菌对抗生素多表现为敏感,推测其生存环境中抗生素的污染较少,同时在对东亚钳蝎人工饲养的场所进行消毒时,要谨慎选择抗生素,防止抗生素使用不当致使东亚钳蝎肠道菌群紊乱引起疾病。     

Role for dopamine in malonate-induced damage in vivo in striatum and in vitro in mesencephalic cultures

Defects in mitochondrial energy metabolism have been implicated in the pathology of several neurodegenerative disorders. In addition, the reactive metabolites generated from the metabolism and oxidation of the neurotransmitter dopamine (DA) are thought to contribute to the damage to neurons of the basal ganglia. We have previously demonstrated that infusions of the metabolic inhibitor malonate into the striata of mice or rats produce degeneration of DA nerve terminals. In the present studies, we demonstrate that an intrastriatal infusion of malonate induces a substantial increase in DA efflux in awake, behaving mice as measured by in vivo microdialysis. Furthermore, pretreatment of mice with tetrabenazine (TBZ) or the TBZ analogue Ro 4-1284 (Ro-4), compounds that reversibly inhibit the vesicular storage of DA, attenuates the malonate-induced DA efflux as well as the damage to DA nerve terminals. Consistent with these findings, the damage to both DA and GABA neurons in mesencephalic cultures by malonate exposure was attenuated by pretreatment with TBZ or Ro-4. Treatment with these compounds did not affect the formation of free radicals or the inhibition of oxidative phosphorylation resulting from malonate exposure alone. Our data suggest that DA plays an important role in the neurotoxicity produced by malonate. These findings provide direct evidence that inhibition of succinate dehydrogenase causes an increase in extracellular DA levels and indicate that bioenergetic defects may contribute to the pathogenesis of chronic neurodegenerative diseases through a mechanism involving DA.     

Scurvy in capybaras bred in captivity in Argentine

In order to determine if the absence of vitamin C in the diet of capybaras (Hydrochoerus hydrochaeris) causes scurvy, a group of seven young individuals were fed food pellets without ascorbic acid, while another group of eight individuals received the same food with 1 g of ascorbic acid per animal per day. Animals in the first group developed signs of scurvy-like gingivitis, breaking of the incisors and death of one animal. Clinical signs appeared between 25 and 104 days from the beginning of the trial in all individuals. Growth rates of individuals deprived of vitamin C was considerably less than those observed in the control group. Deficiency of ascorbic acid had a severe effect on reproduction of another population of captive capybaras. We found that the decrease in ascorbic acid content in the diet affected pregnancy, especially during the first stages. The results obtained suggest that it is necessary to supply a suitable quantity of vitamin C in the diet of this species in captivity.     

Changes in lactate dehydrogenase activity in chicken tissues in hyperthyreosis in ontogenesis

The lactate dehydrogenase activity in reactions of lactate oxidation and synthesis was studied in subfractions of the chicken brain, heart and liver at the embryonal, early postembryonal and adult stages of development after thyroxine administration. It has been shown that during embryogenesis thyroxine predominantly enhanced the rate of lactate oxidation in the mitochondrial tissues. A marked increase in the lactate synthesis was found in cytoplasm of the adult chicken tissues. Specificity of enzyme activity alterations was detected in the chicken brain during ontogenesis after thyroxine administration.     

SSTR5 ablation in islet results in alterations in glucose homeostasis in mice

Somatostatin (SST) peptide is a potent inhibitor of insulin secretion and its effect is mediated via somatostatin receptor 5 (SSTR5) in the endocrine pancreas. To investigate the consequences of gene ablation of SSTR5 in the mouse pancreas, we have generated a mouse model in which the SSTR5 gene was specifically knocked down in the pancreatic beta cells (betaSSTR5Kd) using the Cre-lox system. Immunohistochemistry analysis showed that SSTR5 gene expression was absent in beta cells at three months of age. At the time of gene ablation, betaSSTR5Kd mice demonstrated glucose intolerance with lack of insulin response and significantly reduced serum insulin levels. Insulin tolerance test demonstrated a significant increase of insulin clearance in vivo at the same age. In vitro studies demonstrated an absence of response to SST-28 stimulation in the betaSSTR5Kd mouse islet, which was associated with a significantly reduced SST expression level in betaSSTR5Kd mice pancreata. In addition, betaSSTR5Kd mice had significantly reduced serum glucose levels and increased serum insulin levels at 12 months of age. Glucose tolerance test at an older age also indicated a persistently higher insulin level in betaSSTR5Kd mice. Further studies of betaSSTR5Kd mice had revealed elevated serum C-peptide levels at both 3 and 12 months of age, suggesting that these mice are capable of producing and releasing insulin to the periphery. These results support the hypothesis that SSTR5 plays a pivotal role in the regulation of insulin secretion in the mouse pancreas.