Luo Qixia, Li Meng, Fu Huihui, Meng Qiu, Gao Haichun
Institute of Microbiology and College of Life Sciences, Zhejiang UniversityHangzhou, China; State Key Laboratory for Diagnosis and Treatment of Infectious Disease, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, College of Medicine, The First Affiliated Hospital, Zhejiang UniversityHangzhou, China.
Institute of Microbiology and College of Life Sciences, Zhejiang University Hangzhou, China.
Front Microbiol. 2016 Mar 16;7:327. doi: 10.3389/fmicb.2016.00327. eCollection 2016.
It is established that Escherichia coli β-ketoacyl-ACP synthase (KAS) I (encoded by EcfabB) is the primary, if not exclusive, factor for elongation of the cis-3-decenoyl-ACP (C10:1-ACP) but not effective with C16:1- or longer-chain-ACPs. To test the extent to which these features apply to KAS I proteins in other species, in this study, we examined the physiological role of FabB in Shewanella oneidensis, an excellent model for researching type II fatty acid synthetic (FAS) system and its regulation. We showed that the loss of either FabA (the enzyme that introduces double bond) or FabB, in the absence of DesA which desaturizes C16 and C18 to generate respective C16:1 and C18:1, leads to a UFA auxotroph. However, fatty acid profiles of membrane phospholipid of the fabA and fabB mutants are significantly different, suggesting that FabB participates in steps beyond elongation of C10:1-ACP. Further analyses demonstrated that S. oneidensis FabB differs from EcFabB in that (i) it is not the only enzyme capable of catalyzing elongation of the cis-3-decenoyl-ACP produced by FabA, (ii) it plays a critical role in elongation of C16:1- and longer-chain-ACPs, and (iii) its overproduction is detrimental.
已确定大肠杆菌β-酮脂酰-ACP合酶（KAS）I（由EcfabB编码）是顺式-3-癸烯酰-ACP（C10:1-ACP）延长的主要因素（即便不是唯一因素），但对C16:1-或更长链的ACP无效。为了测试这些特性在其他物种的KAS I蛋白中的适用程度，在本研究中，我们研究了希瓦氏菌中FabB的生理作用，希瓦氏菌是研究II型脂肪酸合成（FAS）系统及其调控的优秀模型。我们发现，在缺乏使C16和C18去饱和以分别生成C16:1和C18:1的DesA的情况下，FabA（引入双键的酶）或FabB的缺失都会导致不饱和脂肪酸营养缺陷型。然而，fabA和fabB突变体的膜磷脂脂肪酸谱有显著差异，这表明FabB参与了C10:1-ACP延长之外的步骤。进一步分析表明，希瓦氏菌FabB与大肠杆菌FabB的不同之处在于：（i）它不是唯一能够催化由FabA产生的顺式-3-癸烯酰-ACP延长的酶；（ii）它在C16:1-和更长链的ACP延长中起关键作用；（iii）其过量表达是有害的。
