Ng Elise Zi Qi, Lee Eunju, Chng Shu-Sin, Kim Jungwook, Guan Xue Li
Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore.
Department of Chemistry, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea.
J Biol Chem. 2025 May 20;301(7):110255. doi: 10.1016/j.jbc.2025.110255.
Biological membranes, which comprise proteins, lipids, and glycans, serve as essential gatekeepers protecting cells from the external environment. In bacteria, phospholipids are a major class of membrane lipids, whose biology has extensively been studied in the Gram-negative organism Escherichia coli. As an adaptive mechanism, E. coli dynamically remodels its phospholipids in response to its environment, which may involve alterations of the structures and/or levels of existing lipids or the incorporation of exogenous substrates to form new phospholipid classes. Intriguingly, an unknown lipid was detected in E. coli and other Enterobacteriaceae. Detection of this lipid in E. coli grown in minimal media suggested its production using an endogenous metabolite. By coupling liquid chromatography mass spectrometry and metabolic incorporation, the lipid was identified as phosphatidylhomoserine (PHS). In E. coli, PHS was produced endogenously by phosphatidylserine synthase A (PssA), confirmed by the absence of PHS in an E. coli ΔpssA mutant, and its inability to incorporate exogenously supplied -homoserine into its phospholipids. Furthermore, purified E. coli PssA (EcPssA) exhibited activity to utilize -homoserine as an alternative substrate to make PHS in vitro. Interestingly, E. coli and other Enterobacteriaceae can decarboxylate PHS to form phosphatidylpropanolamine endogenously. When treated with -homoserine, accumulation of PHS in E. coli was accompanied by a reduction in phosphatidylglycerol and phosphatidylethanolamine, due to competition for common metabolic intermediates. Overall, our findings on the endogenous production of PHS and phosphatidylpropanolamine re-established the baseline phospholipidome of E. coli and provided biochemical and cellular evidence on the substrate promiscuity of EcPssA.
生物膜由蛋白质、脂质和聚糖组成，是保护细胞免受外部环境影响的重要守门者。在细菌中，磷脂是一类主要的膜脂，其生物学特性已在革兰氏阴性菌大肠杆菌中得到广泛研究。作为一种适应性机制，大肠杆菌会根据环境动态重塑其磷脂，这可能涉及现有脂质结构和/或水平的改变，或纳入外源底物以形成新的磷脂类别。有趣的是，在大肠杆菌和其他肠杆菌科细菌中检测到一种未知脂质。在基本培养基中生长的大肠杆菌中检测到这种脂质，表明它是利用内源性代谢物产生的。通过液相色谱质谱联用和代谢掺入技术，该脂质被鉴定为磷脂酰高丝氨酸（PHS）。在大肠杆菌中，PHS由磷脂酰丝氨酸合酶A（PssA）内源性产生，这一点在大肠杆菌ΔpssA突变体中PHS的缺失以及其无法将外源供应的高丝氨酸掺入其磷脂中得到证实。此外，纯化的大肠杆菌PssA（EcPssA）在体外表现出利用高丝氨酸作为替代底物来合成PHS的活性。有趣的是，大肠杆菌和其他肠杆菌科细菌可以将PHS内源性脱羧形成磷脂酰丙醇胺。用高丝氨酸处理时，大肠杆菌中PHS的积累伴随着磷脂酰甘油和磷脂酰乙醇胺的减少，这是由于对共同代谢中间体的竞争所致。总体而言，我们关于PHS和磷脂酰丙醇胺内源性产生的研究结果重新确立了大肠杆菌的基线磷脂组，并为EcPssA的底物混杂性提供了生化和细胞证据。
