School of Natural Sciences, Macquarie University, Sydney, Australia.
ARC Centre of Excellence in Synthetic Biology, Macquarie University, Sydney, Australia.
Environ Microbiol. 2022 Dec;24(12):6071-6085. doi: 10.1111/1462-2920.16168. Epub 2022 Aug 28.
Osmotic stress, caused by high or fluctuating salt concentrations, is a crucial abiotic factor affecting microbial growth in aquatic habitats. Many organisms utilize common responses to osmotic stress, generally requiring active extrusion of toxic inorganic ions and accumulation of compatible solutes to protect cellular machinery. We heterologously expressed and purified predicted osmoprotectant, proline/glycine betaine-binding proteins (ProX) from two phylogenetically distinct Synechococcus spp. MITS9220 and WH8102. Homologues of this protein are conserved only among Prochlorococcus LLIV and Synechococcus clade I, III and CRD1 strains. Our biophysical characterization show Synechococcus ProX exists as a dimer, with specificity solely for glycine betaine but not to other osmoprotectants tested. We discovered that MITS9220_ProX has a 10-fold higher affinity to glycine betaine than WH8102_ProX, which is further elevated (24-fold) in high salt conditions. The stronger affinity and effect of ionic strength on MITS9220_ProX glycine betaine binding but not on WH8102_ProX alludes to a novel regulatory mechanism, providing critical functional insights into the phylogenetic divergence of picocyanobacterial ProX proteins that may be necessary for their ecological success.
渗透胁迫是一种由高盐或波动盐浓度引起的非生物因素，会对水生环境中的微生物生长产生重要影响。许多生物利用共同的渗透胁迫响应机制，通常需要主动排出有毒无机离子并积累相容性溶质以保护细胞机制。我们从两个系统发育上不同的 Synechococcus 菌株 MITS9220 和 WH8102 中异源表达和纯化了预测的渗透保护剂脯氨酸/甘氨酸甜菜碱结合蛋白（ProX）。这种蛋白的同源物仅在 Prochlorococcus LLIV 和 Synechococcus 进化枝 I、III 和 CRD1 菌株中保守。我们的生物物理特性表明，Synechococcus ProX 以二聚体形式存在，对甘氨酸甜菜碱具有特异性，但对其他测试的渗透保护剂没有特异性。我们发现 MITS9220_ProX 对甘氨酸甜菜碱的亲和力比 WH8102_ProX 高 10 倍，在高盐条件下进一步升高（24 倍）。MITS9220_ProX 对甘氨酸甜菜碱结合的亲和力更强，离子强度对其的影响更大，但对 WH8102_ProX 没有影响，这暗示了一种新的调控机制，为研究与生态成功相关的海洋蓝细菌 ProX 蛋白的系统发育分化提供了关键的功能见解。
