SUMO E3连接酶在植物适应非生物胁迫中的作用研究进展

SUMO化(Sumoylation)作为一种广泛存在于真核生物的重要翻译后修饰,在调控植物生长、发育和逆境应答等方面发挥着重要作用。SUMO E3连接酶具有底物识别和选择的作用,直接促进SUMO蛋白与靶蛋白的结合。目前,在植物中已经鉴定出多种SUMO E3连接酶。综述了SUMO E3连接酶在植物适应干旱、盐害、高/低温、营养元素匮缺和重金属毒害等非生物胁迫过程中的作用,并展望了未来植物SUMO化研究的方向,以期为今后植物SUMO化方面的研究提供参考。     

植物蛋白质SUMO化修饰体外高效检测系统

蛋白质SUMO化修饰是一种调控蛋白命运的关键修饰方式, 广泛参与植物生长发育及逆境胁迫响应。SUMO化修饰过程主要由激活酶(E1)-结合酶(E2)-连接酶(E3)组成的级联酶促反应催化, 其关键酶组分将SUMO分子缀合至底物蛋白的赖氨酸残基, 形成共价异肽键以完成SUMO化修饰过程。该文报道了1种植物蛋白质SUMO化修饰体外高效检测系统, 通过在大肠杆菌(Escherichia coli)中构建拟南芥(Arabidopsis thaliana) SUMO化修饰的关键通路实现对底物蛋白的SUMO化修饰, 结果可通过免疫印迹进行检测。该系统可以简化植物蛋白质SUMO化修饰的检测流程, 为植物细胞SUMO化修饰的功能研究提供了有力工具。     

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。     

植物SIZ1 SUMO E3连接酶的研究进展

SUMO化修饰是一种重要的翻译后修饰,对蛋白的翻译后调控起到重要作用。植物SIZ1是一种SUMOE3连接酶,在SUMO化的过程中起着关键作用。本文概述了SIZ1的基本结构和功能,阐述了其在植物响应非生物胁迫如高温、低温、干旱、盐和离子胁迫时所发挥的调节功能,并展望了植物SIZ1研究中有待解决的问题。     

SUMO化修饰系统在哺乳动物胚胎发育及器官发生中的作用

小分子泛素相关修饰物蛋白（small ubiquitin-related modifier protein,SUMO）化修饰是一种广泛存在的蛋白质翻译后修饰形式,存在于动物多个生理和病理过程中,并涉及复杂的信号通路调节过程,是细胞对应激反应的重要调节机制,并且越来越多的研究表明,SUMO化修饰在哺乳动物胚胎发育及器官发生过程中发挥重要作用。在胎儿发育过程中,SUMO化对于器官的形成及发育起着至关重要的作用。SUMO化途径的各组成成分（UBC9、SUMO1～3、PIAS、SENP1～7）在胚胎发育过程中协调胚泡与子宫间的对话、心脏发育以及颅面发育中都发挥着重要作用。在发育过程中SUMO化修饰一旦失调,则可能导致胚胎植入前缺陷、胚胎发育缺陷以及胚胎致死。本综述总结了SUMO化修饰的分子机制,以及SUMO化途径各个组成成分（SUMO、UBC9、PIAS、SENPs）在早期胚胎发育及后续器官发生中功能的最新进展,以望为后续的研究提供借鉴。     

植物蛋白SUMO化修饰检测方法

SUMO化是一种重要的蛋白质翻译后修饰,对植物正常生长发育不可或缺。到目前为止已筛选到上千个可能的SUMO底物,但由于SUMO化修饰水平普遍很低,其生物学功能研究相对较少。该文详细描述了检测蛋白SUMO化修饰的常用方法,包括体外和体内SUMO化实验,以及SUMO化修饰位点的检测方法,旨在为深入研究植物蛋白SUMO化修饰提供技术支持。     

蛋白质SUMO化修饰与肿瘤调控

SUMO化修饰是一种重要的蛋白质翻译后修饰方式,在细胞周期调控、细胞代谢、基因转录、DNA损伤和修复等众多细胞生物学过程中,对底物蛋白质的表达、定位和活性进行调控。蛋白质SUMO化修饰是动态可逆的过程,去SUMO化修饰由SUMO特异性蛋白酶(SENPs)家族成员所催化。由于受到SUMO化修饰的底物蛋白种类众多、功能多样,SUMO化修饰能够在整体和特定蛋白质修饰层面,参与调控肿瘤的发生发展,并且这种调控机制非常复杂,比如调控细胞周期的进程、DNA损伤和基因组不稳定性、肿瘤代谢与生长、抗肿瘤免疫等。SENPs家族成员是底物蛋白质SUMO化修饰程度的决定者,该研究团队对SENPs家族成员在肿瘤中的作用开展了系列研究,因此该文也将以SENP1和SENP3为例,对SENPs在肿瘤进程中的作用及其作用机制展开介绍。     

一种新型SUMO E3连接酶CBX4的化学修饰作用

多梳蛋白家族（polycomb group proteins,PcG）是一类在染色质水平上通过表观遗传修饰抑制靶基因转录的调节因子,它在调节细胞周期、DNA修复、细胞分化、衰老和死亡中起到重要作用。CBX4作为PcG家族中唯一具有SUMO E3 连接酶活性的成员,可以作用于多种底物,包括HIPK2、SIP1、CtBP、CTCF、Dnmt3a和HIF-1α等。底物的SUMO化修饰依赖于特定的结构基础,而且SUMO化的底物功能也会相应发生改变。同时,CBX4还可以被其它分子,如HIPK2, SENP2等进行磷酸化以及去SUMO化等修饰。本篇综述详细阐述了CBX4对底物的SUMO化修饰、自身被修饰及其生物学功能的变化。     

SENPs对肿瘤发展的分子调控机理

SUMO化修饰是一种把小泛素相关修饰物(small ubiquition related modifier,SUMO)共价连接到细胞内靶蛋白半胱氨酸残基上的一种蛋白质翻译后修饰。SUMO化修饰参与并调控着多种细胞进程,如转录调控、核转运和信号转导等。SUMO化修饰是一种动态可逆的修饰方式。SUMO特异性蛋白酶(SUMO-specific proteases,SENPs)可以使SUMO化修饰的蛋白质发生去SUMO化,在维持细胞内SUMO化与去SUMO化的平衡中起重要作用。研究表明,SENPs与多种癌症的发生发展密切相关,如SENP1能直接调节多条致癌通路,诱发正常的前列腺上皮细胞状态异常。癌细胞中的SENP3能诱导血管生成。因此,对去SUMO化机制研究可以为开发癌症治疗药物提供新的思路。     

Structure and analysis of a complex between SUMO and Ubc9 illustrates features of a conserved E2-Ubl interaction

The SUMO E2 Ubc9 serves as a lynchpin in the SUMO conjugation pathway, interacting with the SUMO E1 during activation, with thioester linked SUMO after E1 transfer and with the substrate and SUMO E3 ligases during conjugation. Here, we describe the structure determination of a non-covalent complex between human Ubc9 and SUMO-1 at 2.4 A resolution. Non-covalent interactions between Ubc9 and SUMO are conserved in human and yeast insomuch as human Ubc9 interacts with each of the human SUMO isoforms, and yeast Ubc9 interacts with Smt3, the yeast SUMO ortholog. Structural comparisons reveal similarities to several other non-covalent complexes in the ubiquitin pathway, suggesting that the non-covalent Ubc9-SUMO interface may be important for poly-SUMO chain formation, for E2 recruitment to SUMO conjugated substrates, or for mediating E2 interactions with either E1 or E3 ligases. Biochemical analysis suggests that this surface is less important for E1 activation or di-SUMO-2 formation, but more important for E3 interactions and for poly-SUMO chain formation when the chain exceeds more than two SUMO proteins.     

UHRF2, a Ubiquitin E3 Ligase,Acts as a Small Ubiquitin-like Modifier E3 Ligase for Zinc Finger Protein 131

Small ubiquitin-like modifier (SUMO), a member of the ubiquitin-related protein family, is covalently conjugated to lysine residues of its substrates in a process referred to as SUMOylation. SUMOylation occurs through a series of enzymatic reactions analogous to that of the ubiquitination pathway, resulting in modification of the biochemical and functional properties of substrates. To date, four mammalian SUMO isoforms, a single heterodimeric SUMO-activating E1 enzyme SAE1/SAE2, a single SUMO-conjugating E2 enzyme ubiquitin-conjugating enzyme E2I (UBC9), and a few subgroups of SUMO E3 ligases have been identified. Several SUMO E3 ligases such as topoisomerase I binding, arginine/serine-rich (TOPORS), TNF receptor-associated factor 7 (TRAF7), and tripartite motif containing 27 (TRIM27) have dual functions as ubiquitin E3 ligases. Here, we demonstrate that the ubiquitin E3 ligase UHRF2 also acts as a SUMO E3 ligase. UHRF2 effectively enhances zinc finger protein 131 (ZNF131) SUMOylation but does not enhance ZNF131 ubiquitination. In addition, the SUMO E3 activity of UHRF2 on ZNF131 depends on the presence of SET and RING finger-associated and nuclear localization signal-containing region domains, whereas the critical ubiquitin E3 activity RING domain is dispensable. Our findings suggest that UHRF2 has independent functional domains and regulatory mechanisms for these two distinct enzymatic activities.     

The RanBP2/RanGAP1*SUMO1/Ubc9 complex is a multisubunit SUMO E3 ligase

RanBP2/Nup358 is an essential protein with roles in nuclear transport and mitosis, and is one of the few known SUMO E3 ligases. However, why RanBP2 functions in vivo has been unclear: throughout the cell cycle it stably interacts with RanGAP1*SUMO1 and Ubc9, whose binding sites overlap with the E3 ligase region. Here we show that cellular RanBP2 is quantitatively associated with RanGAP1, indicating that complexed rather than free RanBP2 is the relevant E3 ligase. Biochemical reconstitution of the RanBP2/RanGAP1*SUMO1/Ubc9 complex enabled us to characterize its activity on the endogenous substrate Borealin. We find that the complex is a composite E3 ligase rather than an E2-E3 complex, and demonstrate that complex formation induces activation of a catalytic site that shows no activity in free RanBP2. Our findings provide insights into the mechanism of an important E3 ligase, and extend the concept of multisubunit E3 ligases from ubiquitin to the SUMO field.     

Tag-team SUMO wrestling

Structural and kinetic studies of a SUMORanGAP1-Ubc9-Nup358/RanBP2 complex (Reverter and Lima, 2005) provide the first high-resolution view of SUMO recognition by a SUMO binding motif and also reveal a novel mechanism for E3 ubiquitin-like protein ligases, with the Nup358/RanBP2 E3 teaming up with both SUMO and the E2 (Ubc9) to stimulate tagging.     

DNA activates the Nse2/Mms21 SUMO E3 ligase in the Smc5/6 complex

Modification of chromosomal proteins by conjugation to SUMO is a key step to cope with DNA damage and to maintain the integrity of the genome. The recruitment of SUMO E3 ligases to chromatin may represent one layer of control on protein sumoylation. However, we currently do not understand how cells upregulate the activity of E3 ligases on chromatin. Here we show that the Nse2 SUMO E3 in the Smc5/6 complex, a critical player during recombinational DNA repair, is directly stimulated by binding to DNA. Activation of sumoylation requires the electrostatic interaction between DNA and a positively charged patch in the ARM domain of Smc5, which acts as a DNA sensor that subsequently promotes a stimulatory activation of the E3 activity in Nse2. Specific disruption of the interaction between the ARM of Smc5 and DNA sensitizes cells to DNA damage, indicating that this mechanism contributes to DNA repair. These results reveal a mechanism to enhance a SUMO E3 ligase activity by direct DNA binding and to restrict sumoylation in the vicinity of those Smc5/6‐Nse2 molecules engaged on DNA.     

How DNA vicinity controls SUMO E3 ligase activity

Little is known about the regulation of SUMO E3 ligases and how they are activated upon stress. New findings from the Reverter and Torres‐Rosell laboratories in The EMBO Journal demonstrate that vicinity of preferentially ssDNA activates the SUMO E3 ligase Nse2 when in complex with SMC5‐6.     

Systematic determinations of SUMOylation activation intermediates and dynamics by a sensitive and quantitative FRET assay

Ubiquitination and SUMOylation are multi-step cascade reactions, in which small protein modifiers are activated by E1 activating enzyme, transferred to E2 conjugating enzyme, and conjugated to substrates mediated by the E3 ligase in vivo. The structural and biochemical bases for the cascade reactions have been elucidated by several studies. However, the reaction intermediates and dynamics of these peptide modifiers among the enzymes have not been completely elucidated. Here we report detailed investigations of SUMOylation dynamics and interaction switches of SUMO1 among its ligases using FRET technology. These studies show that, while SUMO1 and the E1 subunit Aos1 or Uba2 have no intrinsic affinity for each other, the adenylation of SUMO1 carried out by Aos1 requires the presence of Uba2, and subsequently conformational changes trigger the interaction of SUMO1 and Uba2 for a thioester bond formation. The reaction intermediates among SUMO1 and its ligases are indirectly revealed by FRET signals generated by each pair. Furthermore, the transfer of SUMO1 from Uba2 to E2 enzyme, Ubc9, depends on the formation of a thioester bond between SUMO1 and Ubc9, and requires non-covalent interaction between Ubc9 and Uba2, but not between Ubc9 and SUMO1. These interaction switches provide the physical and biochemical bases for the SUMO activation and a transfer cascade required for SUMO activation.