Man Weng Chi, Miyazaki Makoto, Chu Kiki, Ntambi James
Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
J Lipid Res. 2006 Sep;47(9):1928-39. doi: 10.1194/jlr.M600172-JLR200. Epub 2006 Jun 2.
Stearoyl-coenzyme A desaturase (SCD) is an endoplasmic reticulum (ER) protein that catalyzes the Delta9-cis desaturation of saturated fatty acids. Mice with targeted disruption in SCD1 (Scd1(-/-)) have significant reduction in the tissue content of triglycerides, suggesting that monounsaturated fatty acids endogenously synthesized by SCD1 are important for triglyceride synthesis. Acyl-coenzyme A:diacylglycerol acyltransferase (DGAT) is the enzyme that catalyzes the final reaction in the synthesis of triglycerides. The lack of DGAT2, one of the two DGAT isoforms, results in almost a complete loss of tissue triglycerides. We hypothesize that SCD1 participates in triglyceride synthesis by providing a more accessible pool of monounsaturated fatty acids through substrate channeling. In this study, we test whether SCD1 is proximal to DGAT2 by colocalization study with confocal microscopy, coimmunoprecipitation, and fluorescence resonance energy transfer using HeLa cells as the model of study. All of the results suggest that SCD1 and DGAT2 are located very close to each other in the ER, which is a very important criterion for the channeling of substrate. By performing subcellular fractionation using mouse livers, we also show, for the first time, that SCD is present in the mitochondria-associated membrane.
硬脂酰辅酶A去饱和酶（SCD）是一种内质网（ER）蛋白，可催化饱和脂肪酸的Δ9-顺式去饱和反应。SCD1基因靶向敲除的小鼠（Scd1(-/-)）组织中甘油三酯含量显著降低，这表明SCD1内源性合成的单不饱和脂肪酸对甘油三酯合成很重要。酰基辅酶A：二酰甘油酰基转移酶（DGAT）是催化甘油三酯合成最后一步反应的酶。两种DGAT同工型之一的DGAT2缺失会导致组织甘油三酯几乎完全丧失。我们推测，SCD1通过底物通道化提供更容易获取的单不饱和脂肪酸池来参与甘油三酯合成。在本研究中，我们以HeLa细胞为研究模型，通过共聚焦显微镜的共定位研究、免疫共沉淀和荧光共振能量转移来检测SCD1是否与DGAT2相邻。所有结果均表明，SCD1和DGAT2在ER中彼此位置非常接近，这是底物通道化的一个非常重要的标准。通过对小鼠肝脏进行亚细胞分级分离，我们还首次证明SCD存在于线粒体相关膜中。
