Keenan Kelly A, Grove Theresa J, Oldham Corey A, O'Brien Kristin M
University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK 99775, United States.
Department of Biology, Valdosta State University, Valdosta, GA 31698, United States.
Comp Biochem Physiol B Biochem Mol Biol. 2017 Feb;204:9-26. doi: 10.1016/j.cbpb.2016.11.001. Epub 2016 Nov 9.
Hearts of Antarctic icefishes (suborder Notothenioidei, family Channichthyidae) have higher densities of mitochondria, and mitochondria have higher densities of phospholipids, compared to red-blooded notothenioids. Glycerol-3-phosphate acyltransferase (GPAT) catalyzes the rate-limiting step in glycerolipid biosynthesis. There are four isoforms of GPAT in vertebrates; GPAT1 and GPAT2 are localized to the outer mitochondrial membrane, whereas GPAT3 and GPAT4 are localized to the endoplasmic reticulum membrane. We hypothesized that transcript levels of GPAT1 and/or GPAT2 would mirror densities of mitochondrial phospholipids and be higher in the icefish Chaenocephalus aceratus compared to the red-blooded species Notothenia coriiceps. Transcript levels of GPAT1 were quantified in heart ventricles and liver using qRT-PCR. Additionally, GPAT1 cDNA was sequenced in the Antarctic notothenioids, C. aceratus and N. coriiceps, and in the sub-Antarctic notothenioid, Eleginops maclovinus, to identify amino acid substitutions that may maintain GPAT1 function at cold temperature. Transcript levels of GPAT1 were higher in liver compared to heart ventricles but were not significantly different between the two species. In contrast, transcripts of GPAT2 were only detected in ventricle where they were 6.6-fold higher in C. aceratus compared to N. coriiceps. These data suggest GPAT1 may be more important for synthesizing triacylglycerol, whereas GPAT2 may regulate synthesis of phospholipids. GPAT1 amino acid sequences are highly conserved among the three notothenioids with 97.9-98.7% identity. Four amino acid substitutions within the cytosolic region of Antarctic notothenioid GPAT1 may maintain conformational changes necessary for binding and catalysis at cold temperature.
与有红血的南极鱼科鱼类相比，南极冰鱼（南极鱼亚目，鳄冰鱼科）的心脏具有更高密度的线粒体，且线粒体具有更高密度的磷脂。甘油-3-磷酸酰基转移酶（GPAT）催化甘油olipid生物合成中的限速步骤。脊椎动物中有四种GPAT同工型；GPAT1和GPAT2定位于线粒体外膜，而GPAT3和GPAT4定位于内质网膜。我们假设，与有红血的小头南极鱼相比，鳄冰鱼中GPAT1和/或GPAT2的转录水平会反映线粒体磷脂的密度且更高。使用qRT-PCR对心室和肝脏中GPAT1的转录水平进行了定量。此外，对南极南极鱼科鱼类鳄冰鱼和小头南极鱼以及亚南极南极鱼科鱼类麦氏突吻鳕的GPAT1 cDNA进行了测序，以鉴定可能在低温下维持GPAT1功能的氨基酸取代。与心室相比，肝脏中GPAT1的转录水平更高，但两个物种之间没有显著差异。相比之下，GPAT2的转录本仅在心室中检测到，在鳄冰鱼中的含量比小头南极鱼高6.6倍。这些数据表明，GPAT1可能对三酰甘油的合成更重要，而GPAT2可能调节磷脂的合成。在这三种南极鱼科鱼类中，GPAT1的氨基酸序列高度保守，同一性为97.9 - 98.7%。南极南极鱼科鱼类GPAT1胞质区域内的四个氨基酸取代可能维持在低温下结合和催化所需的构象变化。
