专肽生物_定制多肽合成服务_多肽合成定制服务_多肽合成厂家_多肽合成公司

Cysteine-rich cationic peptide with antiviral activity against HSV infection and a role in N. gonorrhoeae-mediated HIV enhancement. In contrast to the other members of the ƒ-defensin family it shows very low antimicrobial activity against Gram-negative and Gram-positive bacteria. As a biomarker of colon adenocarcinoma it may have utility in colon cancer screening and diagnosis.

二硫键广泛存在与蛋白结构中，对稳定蛋白结构具有非常重要的意义，二硫键一般是通过序列中的2个Cys的巯基，经氧化形成。
 

形成二硫键的方法很多：空气氧化法，DMSO氧化法，过氧化氢氧化法等。
 

二硫键的合成过程，  可以通过Ellman检测以及HPLC检测方法对其反应进程进行监测。  
   

如果多肽中只含有1对Cys，那二硫键的形成是简单的。多肽经固相或液相合成，然后在pH8-9的溶液中进行氧化。      
 

当需要形成2对或2对以上的二硫键时，合成过程则相对复杂。尽管二硫键的形成通常是在合成方案的最后阶段完成，但有时引入预先形成的二硫化物是有利于连合或延长肽链的。通常采用的巯基保护基有trt, Acm, Mmt, tBu, Bzl, Mob, Tmob等多种基团。我们分别列出两种以2-Cl树脂和Rink树脂为载体合成的多肽上多对二硫键形成路线：
 

二硫键反应条件选择    
 

 二硫键即为蛋白质或多肽分子中两个不同位点Cys的巯基（-SH）被氧化形成的S-S共价键。 一条肽链上不同位置的氨基酸之间形成的二硫键，可以将肽链折叠成特定的空间结构。多肽分 子通常分子量较大，空间结构复杂，结构中形成二硫键时要求两个半胱氨酸在空间距离上接近。 此外，多肽结构中还原态的巯基化学性质活泼，容易发生其他的副反应，而且肽链上其他侧链 也可能会发生一系列修饰，因此，肽链进行修饰所选取的氧化剂和氧化条件是反应的关键因素， 反应机理也比较复杂，既可能是自由基反应，也可能是离子反应。      

反应条件有多种选择，比如空气氧化，DMSO氧化等温和的氧化过程，也可以采用H2O2，I2， 汞盐等激烈的反应条件。
 

空气氧化法： 空气氧化法形成二硫键是多肽合成中最经典的方法，通常是将巯基处于还原态的多肽溶于水中，在近中性或弱碱性条件下（PH值6.5-10），反应24小时以上。为了降低分子之间二硫键形成的可能，该方法通常需要在低浓度条件下进行。
 

碘氧化法：将多肽溶于25%的甲醇水溶液或30%的醋酸水溶液中，逐滴滴加10-15mol/L的碘进行氧化，反应15-40min。当肽链中含有对碘比较敏感的Tyr、Trp、Met和His的残基时，氧化条件要控制的更精确，氧化完后，立即加入维生素C或硫代硫酸钠除去过量的碘。 当序列中有两对或多对二硫键需要成环时，通常有两种情况：
 

自然随机成环:       序列中的Cys之间随机成环，与一对二硫键成环条件相似；
 

定点成环：       定点成环即序列中的Cys按照设计要求形成二硫键，反应过程相对复杂。在 固相合成多肽之前，需要提前设计几对二硫键形成的顺序和方法路线，选择不同的侧链 巯基保护基，利用其性质差异，分步氧化形成两对或多对二硫键。       通常采用的巯基保护 基有trt, Acm, Mmt, tBu, Bzl, Mob, Tmob等多种基团。

定义
防御素是具有广泛抗菌活性的小型抗菌肽（AMP）。它在宿主防御感染，炎症，伤口修复和获得性免疫中起重要作用

发现
在1960年代研究兔和豚鼠白细胞裂解物的抗菌活性时，发现了防御素。所谓的富含精氨酸的阳离子肽是由其高阴极电泳活性迁移率定义的，并因其分离和详细的化学表征而引起了人们的关注1。

分类

哺乳动物防御素可根据其结构上的差异被细分为三个主要类别：所述一个防御素，b防御素和q防御素。一个防御素具有广泛的 抗革兰氏阴性菌和革兰氏阳性抗菌活性 细菌，真菌和包膜病毒。b-防御素 主要对革兰氏阴性细菌和酵母具有活性。q-防御素是一种 在猕猴白细胞中发现的含有18个氨基酸和3个二硫键的环状肽2。三种防御素（人类嗜中性粒细胞防御素[HNP] -1，HNP-2和HNP-3）构成人类多形核嗜中性粒细胞（PMN）3的嗜铁粒颗粒中总蛋白质的30-50％。

结构特征
防御素是小的半胱氨酸富含阳离子的蛋白质与18-45个氨基酸，并用3.4〜4.5 kDa的分子量。所有防御素共有一个特征性的三个二硫键基序。这些半胱氨酸二硫键对于防御素的生物活性至关重要。

行动方式
抗菌 活性的具体机制涉及细菌膜的透化作用。它 已经假定各个单体低聚以形成 通过阴离子膜的孔径，虽然证据仅仅是 间接4。

防御素的杀微生物活性是通过阴离子脂质双层的透化作用和随后 细胞内含物的释放而实现的。防御素和 细菌膜之间的相互作用主要受静电力控制。透化的一种机理被认为涉及 细菌膜中离子孔的形成。第二种模型也称为地毯模型，它假定防御素被认为聚集成带正电荷的贴剂 ，该贴剂可 在肽周围的较大区域中和膜的阴离子脂质头基。这种中和破坏 了脂质双层的完整性，导致 出现瞬时间隙并允许离子渗透到膜4中。

功能
防御素是免疫细胞响应细菌感染而产生的抗菌肽。它还在阻止人类宿主细胞对HIV 5的侵袭中起作用，并在小鼠6中诱导针对肿瘤的细胞介导的免疫反应。各种防御素对单核细胞，T细胞和树突状细胞具有趋化活性。 细胞在先天宿主防御过程中产生的防御素可作为 启动，动员和增强适应性免疫宿主防御的信号。

参考

1.     Ganz.T (2003). Defensins: Antimicrobial peptides of innate immunity. Nature, 3,710-720.

2.     Schneider JJ, Unholzer A, Schaller M, Schäfer-Korting M, Korting HC (2005). Human defensins. J Mol Med, 83(8), 587-595.

3.     R I Lehrer, A Barton, K A Daher, S S Harwig, T Ganz, and M E Selsted (1989). Interaction of human defensins with Escherichia coli. Mechanism of bactericidal activity. J Clin Invest, 84(2), 553–561.

4.     Hoover DM, Rajashankar KR, Blumenthal R, Puri A, Oppenheim JJ, Chertov O, Lubkowski J (2000). The structure of human beta-defensin-2 shows evidence of higher order oligomerization. J Biol Chem, 275(42), 32911-32918.
5.     Zhang L, Yu W, He T, Yu J, Caffrey RE, Dalmasso EA, Fu S, Pham T, Mei J, Ho JJ, Zhang W, Lopez P, Ho DD (2002). Contribution of human alpha-defensin 1, 2, and 3 to the anti-HIV-1 activity of CD8 antiviral factor. Science, 303 (5657), 467.
6.     Biragyn A, Ruffini PA, Leifer CA, Klyushnenkova E, Shakhov A, Chertov O, Shirakawa AK, Farber JM, Segal DM, Oppenheim JJ, Kwak LW. Toll-like receptor 4-dependent activation of dendritic cells by beta-defensin 2. Science, 298(5595), 1025-1029.

Definition
Defensins are small antimicrobial peptide (AMP) with a broad spectrum of antibacterial activity. It plays an important role in host defenses against infections, inflammation, wound repair and acquired immunity

Discovery
Defensins were discovered when the antimicrobial activity of rabbit and guinea-pig leukocyte lysates were studied in the 1960’s. The so-called arginine- rich cationic peptides were defined by their high cathodal electrophorectic activity mobility and attracted attention because of their isolation and detailed chemical characterization1.

Classification

The mammalian defensins can be subdivided into three main classes according to their structural differences: the a-defensins, b-defensins and q-defensins. a-Defensins have broad antimicrobial activity against Gram-negative and Gram-positive bacteria, fungi, and enveloped viruses. b-Defensins are mainly active against Gram-negative bacteria and yeast. q-Defensin is a cyclic peptide containing 18 amino acids with three disulfides discovered in macaque leukocytes2. Three defensins (human neutrophil peptide defensin [HNP]-1, HNP-2, and HNP-3) constitute between 30-50% of the total protein in azurophil granules of human polymorphonuclear neutrophils (PMN)3.

Structural Characteristics
Defensins are small cysteine-rich cationic proteins with 18-45 amino acids and with a molecular weight of 3.4 to 4.5 kDa. All defensins share a characteristic three disulfide bond motif. These cysteine disulfide bonds are essential for the biological activities of defensins.

Mode of action
The specific mechanism of antimicrobial activity involves permeabilization of bacterial membranes. It has been postulated that individual monomers oligomerize to form a pore through anionic membranes, although the evidence is only indirect4.

The microbicidal activity of defensins is brought about by permeabilization of anionic lipid bilayers and the subsequent release of cellular contents. Interactions between defensins and bacterial membranes are governed mainly by electrostatic forces. One mechanism of permeabilization is thought to involve the formation of ion pores in bacterial membranes. The second model also known as carpet model assumes that the defensins are thought to aggregate into positively charged patches that neutralize anionic lipid head groups of the membrane over a wide area around the peptides. This neutralization disrupts the integrity of the lipid bilayer, causing transient gaps to arise and allowing ions to permeate the membrane4.

Functions
Defensins are antimicrobial peptides produced by immune cells in response to bacterial infection. It also functions in blocking of human host cell invasion against HIV5 and the induction of cell-mediated immune responses against tumors in mice6. Various defensins have chemotactic activity for monocytes, T cells and dendritic cells. Defensins produced by cells in the course of innate host defense serve as signals which initiate, mobilize, and amplify adaptive immune host defenses.

References 
1.     Ganz.T (2003). Defensins: Antimicrobial peptides of innate immunity. Nature, 3,710-720.

2.     Schneider JJ, Unholzer A, Schaller M, Schäfer-Korting M, Korting HC (2005). Human defensins. J Mol Med, 83(8), 587-595.

3.     R I Lehrer, A Barton, K A Daher, S S Harwig, T Ganz, and M E Selsted (1989). Interaction of human defensins with Escherichia coli. Mechanism of bactericidal activity. J Clin Invest, 84(2), 553–561.

4.     Hoover DM, Rajashankar KR, Blumenthal R, Puri A, Oppenheim JJ, Chertov O, Lubkowski J (2000). The structure of human beta-defensin-2 shows evidence of higher order oligomerization. J Biol Chem, 275(42), 32911-32918.
5.     Zhang L, Yu W, He T, Yu J, Caffrey RE, Dalmasso EA, Fu S, Pham T, Mei J, Ho JJ, Zhang W, Lopez P, Ho DD (2002). Contribution of human alpha-defensin 1, 2, and 3 to the anti-HIV-1 activity of CD8 antiviral factor. Science, 303 (5657), 467.
6.     Biragyn A, Ruffini PA, Leifer CA, Klyushnenkova E, Shakhov A, Chertov O, Shirakawa AK, Farber JM, Segal DM, Oppenheim JJ, Kwak LW. Toll-like receptor 4-dependent activation of dendritic cells by beta-defensin 2. Science, 298(5595), 1025-1029.