MSU-Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI, 48824, USA.
Plant Biology Department, Michigan State University, East Lansing, MI, 48824, USA.
Plant J. 2018 Jun;94(5):836-846. doi: 10.1111/tpj.13900. Epub 2018 Apr 24.
Peroxisomes are dynamic organelles crucial for a variety of metabolic processes during the development of eukaryotic organisms, and are functionally linked to other subcellular organelles, such as mitochondria and chloroplasts. Peroxisomal matrix proteins are imported by peroxins (PEX proteins), yet the modulation of peroxin functions is poorly understood. We previously reported that, besides its known function in chloroplast protein import, the Arabidopsis E3 ubiquitin ligase SP1 (suppressor of ppi1 locus1) also targets to peroxisomes and mitochondria, and promotes the destabilization of the peroxisomal receptor-cargo docking complex components PEX13 and PEX14. Here we present evidence that in Arabidopsis, SP1's closest homolog SP1-like 1 (SPL1) plays an opposite role to SP1 in peroxisomes. In contrast to sp1, loss-of-function of SPL1 led to reduced peroxisomal β-oxidation activity, and enhanced the physiological and growth defects of pex14 and pex13 mutants. Transient co-expression of SPL1 and SP1 promoted each other's destabilization. SPL1 reduced the ability of SP1 to induce PEX13 turnover, and it is the N-terminus of SP1 and SPL1 that determines whether the protein is able to promote PEX13 turnover. Finally, SPL1 showed prevalent targeting to mitochondria, but rather weak and partial localization to peroxisomes. Our data suggest that these two members of the same E3 protein family utilize distinct mechanisms to modulate peroxisome biogenesis, where SPL1 reduces the function of SP1. Plants and possibly other higher eukaryotes may employ this small family of E3 enzymes to differentially modulate the dynamics of several organelles essential to energy metabolism via the ubiquitin-proteasome system.
过氧化物酶体是真核生物发育过程中各种代谢过程所必需的动态细胞器，并且与其他亚细胞细胞器（如线粒体和叶绿体）在功能上相关联。过氧化物酶体基质蛋白通过过氧化物酶体（PEX 蛋白）导入，但过氧化物酶体功能的调节知之甚少。我们之前的研究表明，除了在叶绿体蛋白导入中已知的功能外，拟南芥 E3 泛素连接酶 SP1（ppi1 基因座 1 的抑制物）还靶向过氧化物体和线粒体，并促进过氧化物体受体-货物对接复合物成分 PEX13 和 PEX14 的不稳定性。在这里，我们提供的证据表明，在拟南芥中，SP1 的最接近的同源物 SP1-like 1（SPL1）在过氧化物体中与 SP1 发挥相反的作用。与 sp1 相反，SPL1 的功能丧失导致过氧化物体β-氧化活性降低，并增强了 pex14 和 pex13 突变体的生理和生长缺陷。SPL1 和 SP1 的瞬时共表达促进了彼此的不稳定。SPL1 降低了 SP1 诱导 PEX13 周转的能力，并且是 SP1 和 SPL1 的 N 端决定了该蛋白是否能够促进 PEX13 周转。最后，SPL1 显示出普遍靶向线粒体，但靶向过氧化物体的能力较弱且部分定位。我们的数据表明，同一 E3 蛋白家族的这两个成员利用不同的机制来调节过氧化物体的生物发生，其中 SPL1 降低了 SP1 的功能。植物和可能的其他高等真核生物可能利用这种小的 E3 酶家族通过泛素-蛋白酶体系统来差异调节对能量代谢至关重要的几种细胞器的动态。
