SUMO化修饰与DNA损伤修复

蛋白质的翻译后修饰在很大程度上决定了蛋白质的活性、细胞定位、稳定性及蛋白质之间的相互作用.而在DNA损伤修复过程中,通过调控不同修复蛋白的翻译后修饰来影响他们的活性及细胞定位,进而导致DNA损伤修复途径的不同和修复结果的差异.新近研究表明,蛋白质的SUMO化修饰在DNA损伤修复和基因组稳定性的维护方面发挥重要作用.本文将对SUMO化修饰对DNA损伤修复的调控的最新研究进展做一综述.     

植物SUMO化修饰及其生物学功能

SUMO化修饰是细胞内蛋白质功能调节的重要方式之一。植物中的SUMO化修饰途径由SUMO分子和SUMO化酶系组成。SUMO化修饰是一个可逆的动态过程。SUMO前体蛋白在SUMO特异性蛋白酶的作用下成熟, 随后通过SUMO活化酶、SUMO结合酶和SUMO连接酶将靶蛋白SUMO化, 最后SUMO特异性蛋白酶将SUMO与靶蛋白分离, 重新进入SUMO化循环。初步研究表明, 植物SUMO化修饰参与植物花期调控、激素信号转导、抗病防御以及逆境应答等生理过程。     

植物SUMO化修饰及其生物学功能

SUMO化修饰是细胞内蛋白质功能调节的重要方式之一。植物中的SUMO化修饰途径由SUMO分子和SUMO化酶系组成。SUMO化修饰是一个可逆的动态过程。SUMO前体蛋白在SUMO特异性蛋白酶的作用下成熟,随后通过SUMO活化酶、SUMO结合酶和SUMO连接酶将靶蛋白SUMO化,最后SUMO特异性蛋白酶将SUMO与靶蛋白分离,重新进入SUMO化循环。初步研究表明,植物SUMO化修饰参与植物花期调控、激素信号转导、抗病防御以及逆境应答等生理过程。     

小泛素相关修饰物SUMO研究进展

蛋白质翻译后修饰对改变蛋白功能、活性或定位都起着非常重要的作用,泛素及其相似蛋白的修饰是其中一种重要形式。与其他诸如磷酸化、乙酰化、糖基化等不同的是,泛素及其相似蛋白的修饰基团本身即是一个小的多肽,通过异肽键与靶蛋白Lys侧链ε-NH2相连,其中小泛素相关修饰物(small ubiquitin—related modifier,SUMO)与蛋白的共价连接是一种新的广泛存在的翻译后修饰形式。SUMO是广泛存在于真核生物中高度保守的蛋白家族,在脊椎动物中有三个SUMO基因,称为SUMO-1,-2,-3,与泛素在二级结构上极其相似,且催化修饰过程的酶体系也具有很高的同源性。然而,与泛素化介导的蛋白酶降解途径不同,SUMO化修饰发挥着更为广泛的功能,如核质转运、细胞周期调控、信号转导、转录活性调控等。     

植物SUMO化修饰研究进展

SUMO化修饰是一种高度保守的蛋白质翻译后修饰。在SUMO化酶系统的协同作用下,成熟的SUMO分子以异肽键的方式结合到靶蛋白上,调控靶蛋白稳定性、活性、定位等。同时,发生SUMO化修饰的蛋白在SUMO特异蛋白酶的作用下发生去SUMO化反应,使SUMO重新进入循环过程。已知SUMO化修饰参与了植物胁迫响应、生长发育、开花等重要生理过程的调控。本文主要介绍了植物SUMO化修饰途径及其调控的生物学过程,并讨论蛋白组学方法在SUMO化修饰底物鉴定的进展及问题。     

蛋白质多聚SUMO化修饰及其功能

泛素（ubiquitin, Ub）是一类高度保守的小蛋白, 可与靶蛋白的赖氨酸残基共价连接, 形成多聚泛素链行使功能. 类似于泛素化修饰过程, 小泛素相关修饰物(small ubiquitin related modifier, SUMO）也可以共价修饰靶蛋白的赖氨酸残基, 从而影响靶蛋白的定位、稳定性以及蛋白间的相互作用, 发挥重要的生理功能. 尽管在多数情况下, 靶蛋白发生的是单SUMO化修饰, 但最近研究发现,SUMO依赖自身的赖氨酸也可以形成多聚链. 与单SUMO化修饰不同的是, 多聚SUMO化修饰的靶蛋白可以进一步被泛素化修饰, 进而诱导靶蛋白的降解. 这是一种新的、特殊的化学修饰形式, 弄清它的生理功能,对于了解细胞的生长、分化以及凋亡等生理过程将具有重要的意义. 本文将就此方面的最新研究进展做一综述.     

SUMO化修饰对NF-kB信号通路的调控

小泛素相关修饰物(small ubiquitin-related modifier,SUMO)经由一系列酶介导的生化级联反应共价结合于靶蛋白的赖氨酸残基上,稳定靶蛋白免受降解的过程称为SUMO化修饰(SUMOylation).核转录因子kB(nuclear factors kB,NF-kB)是公认的炎症和免疫反应的重要调节因子,并与糖尿病的发生发展密切相关.近年来研究发现,不仅NF-kB抑制蛋白(inhibitor of NF-kB,IkB)的SUMO化修饰参与NF-kB信号通路的调节,而且SUMO酶可以直接调节NF-kB对靶基因的转录.现就SUMO亚型及结构,SUMO化修饰与去SUMO化修饰过程,SUMO、SUMO酶对NF-kB的转录调控及其与糖尿病相关性的最新研究进展作以综述.     

蛋白质的类泛素化修饰

SUMO(small ubiquitin-related modifier)是一类重要的类泛素蛋白,在生物进化过程中高度保守,其三维结构及生化修饰过程与泛素类似,但该两类蛋白质修饰的生物学意义却不尽相同。SUMO化修饰作为一种重要的蛋白质翻译后修饰,广泛参与细胞活动的各个方面,且SUMO化修饰异常与许多人类重大疾病密切相关。     

SUMO化和磷酸化的相互作用与共同修饰

翻译后修饰如磷酸化、乙酰化、甲基化、泛素化和SUMO化调节不同蛋白质的不同功能。磷酸化可能是最常见的修饰之一,蛋白质磷酸化通过一系列的激酶和磷酸酶催化,从而改变蛋白质功能。SUMO修饰是一种类泛素化修饰。SUMO修饰包括活化、结合、连接和解离,涉及多个酶多个步骤的催化过程。SUMO化可调节蛋白质相互作用、亚细胞定位、蛋白质稳定性和转录活性。关于磷酸化和SUMO化的蛋白质翻译后修饰,已有广泛研究报道。但很少关注于磷酸化和SUMO化之间的相互作用,以及它们对蛋白质的共同修饰。本文综述了蛋白质磷酸化和SUMO化之间的相互作用,以及共同修饰对细胞生理和肿瘤的影响。     

SUMO化和磷酸化的相互作用和共同修饰

翻译后修饰如磷酸化、乙酰化、甲基化、泛素化和SUMO化调节不同蛋白质的不同功能。磷酸化可能是最常见的修饰之一,蛋白质磷酸化通过一系列的激酶和磷酸酶催化,从而改变蛋白质功能。SUMO修饰是一种类泛素化修饰。SUMO修饰包括活化、结合、连接和解离,涉及多个酶多个步骤的催化过程。SUMO化可调节蛋白质相互作用、亚细胞定位、蛋白质稳定性和转录活性。关于磷酸化和SUMO化的蛋白质翻译后修饰,已有广泛研究报道。但很少关注于磷酸化和SUMO化之间的相互作用,以及它们对蛋白质的共同修饰。本文综述了蛋白质磷酸化和SUMO化之间的相互作用,以及共同修饰对细胞生理和肿瘤的影响。     

Role of SUMO modification of human PCNA at stalled replication fork

DNA double-strand breaks (DSBs) can be generated not only by reactive agents but also as a result of replication fork collapse at unrepaired DNA lesions. Whereas ubiquitylation of proliferating cell nuclear antigen (PCNA) facilitates damage bypass, modification of yeast PCNA by small ubiquitin-like modifier (SUMO) controls recombination by providing access for the Srs2 helicase to disrupt Rad51 nucleoprotein filaments. However, in human cells, the roles of PCNA SUMOylation have not been explored. Here, we characterize the modification of human PCNA by SUMO in vivo as well as in vitro. We establish that human PCNA can be SUMOylated at multiple sites including its highly conserved K164 residue and that SUMO modification is facilitated by replication factor C (RFC). We also show that expression of SUMOylation site PCNA mutants leads to increased DSB formation in the Rad18(-/-) cell line where the effect of Rad18-dependent K164 PCNA ubiquitylation can be ruled out. Moreover, expression of PCNA-SUMO1 fusion prevents DSB formation as well as inhibits recombination if replication stalls at DNA lesions. These findings suggest the importance of SUMO modification of human PCNA in preventing replication fork collapse to DSB and providing genome stability.     

Rad52 SUMOylation affects the efficiency of the DNA repair

Homologous recombination (HR) plays a vital role in DNA metabolic processes including meiosis, DNA repair, DNA replication and rDNA homeostasis. HR defects can lead to pathological outcomes, including genetic diseases and cancer. Recent studies suggest that the post-translational modification by the small ubiquitin-like modifier (SUMO) protein plays an important role in mitotic and meiotic recombination. However, the precise role of SUMOylation during recombination is still unclear. Here, we characterize the effect of SUMOylation on the biochemical properties of the Saccharomyces cerevisiae recombination mediator protein Rad52. Interestingly, Rad52 SUMOylation is enhanced by single-stranded DNA, and we show that SUMOylation of Rad52 also inhibits its DNA binding and annealing activities. The biochemical effects of SUMO modification in vitro are accompanied by a shorter duration of spontaneous Rad52 foci in vivo and a shift in spontaneous mitotic recombination from single-strand annealing to gene conversion events in the SUMO-deficient Rad52 mutants. Taken together, our results highlight the importance of Rad52 SUMOylation as part of a ‘quality control’ mechanism regulating the efficiency of recombination and DNA repair.     

The CTCF Insulator Protein Is Posttranslationally Modified by SUMO

The CTCF protein is a highly conserved zinc finger protein that is implicated in many aspects of gene regulation and nuclear organization. Its functions include the ability to act as a repressor of genes, including the c-myc oncogene. In this paper, we show that the CTCF protein can be posttranslationally modified by the small ubiquitin-like protein SUMO. CTCF is SUMOylated both in vivo and in vitro, and we identify two major sites of SUMOylation in the protein. The posttranslational modification of CTCF by the SUMO proteins does not affect its ability to bind to DNA in vitro. SUMOylation of CTCF contributes to the repressive function of CTCF on the c-myc P2 promoter. We also found that CTCF and the repressive Polycomb protein, Pc2, are colocalized to nuclear Polycomb bodies. The Pc2 protein may act as a SUMO E3 ligase for CTCF, strongly enhancing its modification by SUMO 2 and 3. These studies expand the repertoire of posttranslational modifications of CTCF and suggest roles for such modifications in its regulation of epigenetic states.     

SUMO-1 controls the protein stability and the biological function of phosducin

Phosducin regulates Gbetagamma-stimulated signaling by binding to Gbetagamma subunits of heterotrimeric G-proteins. Control of phosducin activity by phosphorylation is well established. However, little is known about other mechanisms that may control phosducin activity. Here we report that phosducin is regulated at the posttranslational level by modification with the small ubiquitin-related modifier, SUMO. We demonstrate modification with SUMO for phosducin in vitro expressed in cells and for native phosducin purified from retina and the heart. A consensus motif for SUMOylation was identified in phosducin at amino acid positions 32-35. Mutation of the conserved lysine 33 to arginine in this motif abolished SUMOylation of phosducin, indicating that SUMO is attached to lysine 33 of phosducin. In transfected cells the steady-state levels of the K33R mutant protein were much lower compared with wild-type phosducin. The investigation of the stability of wild-type phosducin and of phosducinK33R showed a decreased protein stability of the SUMOylation-deficient mutant. The decreased protein stability correlated with increased ubiquitinylation of the SUMOylation-deficient mutant. These findings indicate that SUMOylation protects phosducin from proteasomal degradation. SUMOylation of phosducin decreased its ability to bind Gbetagamma. PhlP, a closely related member of the phosducin family, was not a target for SUMOylation, but its SUMOylation can be achieved by a single amino acid insertion in the conserved N terminus of PhlP. Together, these findings show that phosducin is a previously unrecognized target of SUMO modification and that SUMOylation controls phosducin stability in cells as well as its functional properties.     

HIF-1α的可逆性SUMO化修饰

低氧诱导因子1(hypoxia inducible factor-1, HIF-1)是参与调节机体氧平衡的重要转录因子,在细胞低氧应答反应中起核心作用,能调节100多种涉及低氧应激下细胞适应和存活的靶基因．HIF-1由氧敏感的α亚基和在细胞内稳定表达的β亚基组成．其中α亚基可受到多种翻译后化学修饰作用,如在常氧下,HIF-1α通过泛素化蛋白酶修饰并导致其快速降解．最近几年发现的泛素样蛋白家族成员小泛素蛋白样修饰蛋白（SUMO）也能与HIF-1α共价结合．SUMO是一种分子量约为12 kD的小蛋白,从拟南芥到人类普遍存在．SUMO可共价结合许多靶底物蛋白,并对其进行翻译后修饰,该过程称为SUMO化．与泛素化蛋白酶体途径不同的是,SUMO化修饰能在常氧和相对低氧的条件下调节HIF-1α蛋白的稳定性,从而改变其转录活性．SUMO化是一个可逆的动态过程,可被特异性蛋白酶ULP/SENP将其从底物上去除．本文主要就HIF-1α的可逆性SUMO化修饰作一综述．     

类泛素化修饰蛋白SUMO1的表达纯化及抗体制备

SUMO是近年发现的类泛素化修饰蛋白,可通过异肽键共价连接到靶蛋白上,影响靶蛋白的细胞内定位、稳定性及与其它生物大分子的相互作用. 为研究蛋白质的SUMO化修饰,本文表达并利用亲和层析的方法纯化了重组的人SUMO1,制备了兔抗hSUMO1的多克隆抗体. 经ELISA和免疫印迹检测,获得了灵敏度高、特异性好的抗体,可用于SUMO化修饰靶蛋白的鉴定及SUMO化修饰的生物学功能研究.