| 摘要: | 蛋白質經後修飾作用 (post-translational modification) ，使其具有不同功能與特性，藉此調節細胞生理活性。其中以ubiquitination和SUMOylation形成機制最為相似，皆使用多個酵素將標的蛋白質接上ubiquitin或SUMO。研究顯示，標的蛋白質上ubiquitin透過特定離胺酸 (Lysine) 形成多個Ub-Ub鍵結，稱之poly-Ub chains，而ubiquitin上不同Lysine所形成poly-Ub鍵結代表不同的生理意義。
在SUMOylation研究中發現，SUMO也會在標的蛋白質上形成poly-SUMO chains。目前已知在低等真核生物中poly-SUMO chains與酵母菌孢子的形成有關。此外，在高等真核生物中也發現了生理壓力下會促使poly-hSUMO-1 chains形成之現象。但目前仍不清楚SUMO-1上哪個Lysine與形成poly-hSUMO-1 chains有關以及poly-SUMO-1 chains在高等真核生物中所代表的意義。
因此，本研究首先將hSUMO-1所有離胺酸全都突變成精胺酸，稱為K0，以K0當控制組來觀察單一離胺酸還原之hSUMO-1，K1至K11，並探討hSUMO-1上哪些離胺酸可能是hSUMO-1上形成聚合鏈之分支點。結果發現，當標的蛋白質進行SUMOylation修飾時，除了標的蛋白質上之離胺酸會連結一個hSUMO-1之外，而且hSUMO-1本身也會進行SUMOylation修飾，透過hSUMO-1上之Lys 17、Lys 23、Lys 25、Lys39、Lys45、Lys46、Lys 48、Lys 78進行SUMOylaiton，其中又以Lys48主要是形成SUMOylation之位置，而且這些分支點可能是形成poly-SUMO-1 chains之位置。因此，本研究之結果可提供hSUMO-1與hSUMO-1如何進行連結，藉此可進一步探討poly-SUMO-1 chains對於高等真核生物之生理意義。
The post-translational modification, such as phosphorylation, methylation, acetylation, ubiquitination, and SUMOylation plays a vital role in altering properties and functions of cellular protein. Among these modifications, ubiquitination and SUMOylation share a similar mechanism of a set of three catalytic enzymes facilitating the conjugation of ubiquitin or SUMO protein to the target protein. Recent studies showed that ubiquitination occurs on the specific lysine site of target proteins and different ubiquitination formation linkages represent unique biological significances.
In the field of SUMOylation studies, scientists also observed poly-SUMO chains formation. This phenomenon is vital in yeast spore formation. Besides, poly-SUMO chains formation was regulated under physiological stress. However, it is still unclear at the biological significance of poly-SUMO chains formation and which lysine of SUMO-1 is involved in poly-SUMO chains formation. In this study, human cell lines were used to investigate the biological functions of poly-SUMO chains and the branch point of poly-SUMO chains formation.
In order to identify which lysine of hSUMO-1 is the branch point for poly-SUMOylation, we initially mutated all lysine on hSUMO-1 to arginine, which is K0 hSUMO-1. We then compared SUMOylation pattern of the different single lysine revertant of hSUMO-1, which are called K1~K11, with K0. We found that hSUMO-1 can be modified by SUMOylation through Lys17, Lys23, Lys25, Lys39, Lys45, Lys 48, and Lys78 of hSUMO-1. Among the SUMO modified lysines, Lys48 seemed to be the major SUMOylation site, suggesting that these branch points might be potential SUMOylaion sites for poly-SUMO-1 chains. These results offer new insight into conjugation of hSUMO-1 and study of the biological functions of poly-SUMO-1 chains. |
