Study on a Novel Cold-Active and Halotolerant Monoacylglycerol Lipase Widespread in Marine Bacteria Reveals a New Group of Bacterial Monoacylglycerol Lipases Containing Unusual C(A/S)HSMG Catalytic Motifs
Study on a Novel Cold-Active and Halotolerant Monoacylglycerol Lipase Widespread in Marine Bacteria Reveals a New Group of Bacterial Monoacylglycerol Lipases Containing Unusual C(A/S)HSMG Catalytic Motifs
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对海洋细菌中广泛存在的新型冷活性和耐盐单酰甘油脂肪酶的研究揭示了一组新的含有不寻常 C(A/S)HSMG 催化基序的细菌单酰甘油脂肪酶
DOI：
10.3389/fmicb.2020.00009
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发表时间：
2020-01-23
影响因子：
5.2
通讯作者：
Chen, Xiu-Lan
中科院分区：
文献类型：
--
作者：
Li, Ping-Yi;Zhang, Yan-Qi;Chen, Xiu-Lan
单酰基甘油脂肪酶（MGL）存在于生命的所有领域。然而，关于细菌MGL的报道仍然有限。迄今为止，已报道的细菌MGL都是来自温暖陆地环境或深海热液喷口的嗜热/中温酶，没有一种来源于低温、高盐和贫营养的海洋环境。在这里，我们的特点是一种新的MGL，GnMgl，从海洋冷适应和嗜盐细菌Glaciecola nitratireducens FR 1064 T。GnMgl与表征的MGL具有相当低的序列相似性（低于31%）。GnMgl及其大多数细菌同源物具有位于保守的C（A/S）HSMG基序中的催化Ser残基，而不是位于其他MGL上报道的典型GxSxG基序中，这表明GnMgl样酶可能在催化方面不同于报道的MGL。系统发育分析表明，GnMgl及其细菌同源物聚为水解酶_4超家族的单甘油酯脂肪酶_溶血磷脂酶家族中的一个独立的组。重组GnMgl不具有溶血磷脂酶活性，但可以水解饱和（C12：0-C16：0）和不饱和（C18：1和C18：2）MG和短链三酰甘油，显示出与报道的细菌MGL不同的底物选择性。GnMgl的底物偏好性，预测为膜蛋白，与菌株FR 1064 T内最丰富的脂肪酸相关，表明GnMgl在该海洋细菌中的脂质催化剂中的作用。此外，与已知的细菌MGL都是热稳定酶不同，GnMgl是一种冷适应酶，在30 ℃时活性最大，在0 ℃时保留30%的活性。GnMgl也是在3.5M NaCl中具有完全活性的耐盐酶。GnMgl的耐冷和耐盐特性可能有助于其源菌株FR 1064 T适应寒冷和盐的海洋环境。此外，GnMgl的同源物被发现在各种海洋细菌中丰富，暗示它们在这些海洋细菌中的重要生理作用。我们对GnMgl的研究结果揭示了海洋MGL。
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 Glaciecola nitratireducens FR1064T. 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 FR1064T, 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 FR1064T 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.