Li Ping-Yi, Zhang Yan-Qi, Zhang Yi, Jiang Wen-Xin, Wang Yan-Jun, Zhang Yi-Shuo, Sun Zhong-Zhi, Li Chun-Yang, Zhang Yu-Zhong, Shi Mei, Song Xiao-Yan, Zhao Long-Sheng, Chen Xiu-Lan
State Key Laboratory of Microbial Technology, Marine Biotechnology Research Center, Shandong University, Qingdao, China.
Department of Hematology, Qilu Hospital, Shandong University, Jinan, China.
Front Microbiol. 2020 Jan 23;11:9. doi: 10.3389/fmicb.2020.00009. eCollection 2020.
Monoacylglycerol lipases (MGLs) are present in all domains of life. However, reports on bacterial MGLs are still limited. Until now, reported bacterial MGLs are all thermophilic/mesophilic enzymes from warm terrestrial environments or deep-sea hydrothermal vent, and none of them originates from marine environments vastly subject to low temperature, high salts, and oligotrophy. Here, we characterized a novel MGL, GnMgl, from the marine cold-adapted and halophilic bacterium FR1064. GnMgl shares quite low sequence similarities with characterized MGLs (lower than 31%). GnMgl and most of its bacterial homologs harbor a catalytic Ser residue located in the conserved C(A/S)HSMG motif rather than in the typical GxSxG motif reported on other MGLs, suggesting that GnMgl-like enzymes might be different from reported MGLs in catalysis. Phylogenetic analysis suggested that GnMgl and its bacterial homologs are clustered as a separate group in the monoglyceridelipase_lysophospholipase family of the Hydrolase_4 superfamily. Recombinant GnMgl has no lysophospholipase activity but could hydrolyze saturated (C12:0-C16:0) and unsaturated (C18:1 and C18:2) MGs and short-chain triacylglycerols, displaying distinct substrate selectivity from those of reported bacterial MGLs. The substrate preference of GnMgl, predicted to be a membrane protein, correlates to the most abundant fatty acids within the strain FR1064, suggesting the role of GnMgl in the lipid catabolism in this marine bacterium. In addition, different from known bacterial MGLs that are all thermostable enzymes, GnMgl is a cold-adapted enzyme, with the maximum activity at 30°C and retaining 30% activity at 0°C. GnMgl is also a halotolerant enzyme with full activity in 3.5M NaCl. The cold-adapted and salt-tolerant characteristics of GnMgl may help its source strain FR1064 adapt to the cold and saline marine environment. Moreover, homologs to GnMgl are found to be abundant in various marine bacteria, implying their important physiological role in these marine bacteria. Our results on GnMgl shed light on marine MGLs.
单酰甘油脂肪酶（MGLs）存在于生命的所有领域。然而，关于细菌MGLs的报道仍然有限。到目前为止，已报道的细菌MGLs都是来自温暖陆地环境或深海热液喷口的嗜热/嗜温酶，没有一种来源于受低温、高盐和贫营养影响极大的海洋环境。在此，我们对一种来自海洋冷适应嗜盐细菌FR1064的新型MGL（GnMgl）进行了表征。GnMgl与已表征的MGLs的序列相似性相当低（低于31%）。GnMgl及其大多数细菌同源物在保守的C(A/S)HSMG基序中含有一个催化性丝氨酸残基，而不是在其他MGLs报道的典型GxSxG基序中，这表明GnMgl样酶在催化作用上可能与已报道的MGLs不同。系统发育分析表明，GnMgl及其细菌同源物在水解酶_4超家族的甘油单酯脂肪酶_溶血磷脂酶家族中聚为一个单独的类群。重组GnMgl没有溶血磷脂酶活性，但能水解饱和（C12:0 - C16:0）和不饱和（C18:1和C18:2）单酰甘油以及短链三酰甘油，显示出与已报道的细菌MGLs不同的底物选择性。预测为膜蛋白的GnMgl的底物偏好与菌株FR1064中最丰富的脂肪酸相关，这表明GnMgl在这种海洋细菌的脂质分解代谢中的作用。此外，与所有已知的细菌MGLs都是热稳定酶不同，GnMgl是一种冷适应酶，在30°C时活性最高，在0°C时仍保留30%的活性。GnMgl也是一种耐盐酶，在3.5M NaCl中具有完全活性。GnMgl的冷适应和耐盐特性可能有助于其来源菌株FR1064适应寒冷和高盐的海洋环境。此外，发现GnMgl的同源物在各种海洋细菌中丰富，这意味着它们在这些海洋细菌中具有重要的生理作用。我们对GnMgl的研究结果为海洋MGLs提供了新的认识。
