CSIR-Centre for Cellular and Molecular Biology, Hyderabad, Telangana, India.
Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh, India.
J Bacteriol. 2023 Jan 26;205(1):e0038222. doi: 10.1128/jb.00382-22. Epub 2022 Dec 12.
Peptidoglycan (PG) is a unique and essential component of the bacterial cell envelope. It is made up of several linear glycan polymers cross-linked through covalently attached stem peptides making it a fortified mesh-like sacculus around the bacterial cytosolic membrane. In most bacteria, including Escherichia coli, the stem peptide is made up of l-alanine (l-Ala), d-glutamate (d-Glu), meso-diaminopimelic acid (mDAP), d-alanine (d-Ala), and d-Ala with cross-links occurring either between d-ala and mDAP or between two mDAP residues. Of these, the cross-links of the 4-3 (d-Ala-mDAP) type are the most predominant and are formed by penicillin-binding D,D-transpeptidases, whereas the formation of less frequent 3-3 linkages (mDAP-mDAP) is catalyzed by L,D-transpeptidases. In this study, we found that the frequency of the 3-3 cross-linkages increased upon cold shock in exponentially growing E. coli and that the increase was mediated by an L,D-transpeptidase, LdtD. We found that a cold-inducible RNA helicase DeaD enhanced the cellular LdtD level by facilitating its translation resulting in an increased abundance of 3-3 cross-linkages during cold shock. However, DeaD was also required for optimal expression of LdtD during growth at ambient temperature. Overall, our study finds that E. coli undergoes PG remodeling during cold shock by altering the frequency of 3-3 cross-linkages, implying a role for these modifications in conferring fitness and survival advantage to bacteria growing in diverse environmental conditions. Most bacteria are surrounded by a protective exoskeleton called peptidoglycan (PG), an extensively cross-linked mesh-like macromolecule. In bacteria, such as Escherichia coli, the cross-links in the PG are of two types: a major fraction is of 4-3 type whereas a minor fraction is of 3-3 type. Here, we showed that E. coli exposed to cold shock had elevated levels of 3-3 cross-links due to the upregulation of an enzyme, LdtD, that catalyzed their formation. We showed that a cold-inducible RNA helicase DeaD enhanced the cellular LdtD level by facilitating its translation, resulting in increased 3-3 cross-links during cold shock. Our results suggest that PG remodeling contributes to the survival and fitness of bacteria growing in conditions of cold stress.
肽聚糖 (PG) 是细菌细胞包膜的独特且必需的组成部分。它由几个线性聚糖聚合物通过共价连接的 直链肽交联组成，形成围绕细菌胞质膜的强化网格状囊泡。在大多数细菌中，包括大肠杆菌，直链肽由 l-丙氨酸 (l-Ala)、d-谷氨酸 (d-Glu)、meso-二氨基庚二酸 (mDAP)、d-丙氨酸 (d-Ala) 和 d-丙氨酸组成，交联发生在 d-ala 和 mDAP 之间或两个 mDAP 残基之间。其中，4-3 (d-Ala-mDAP) 型交联最为常见，由青霉素结合 D,D-转肽酶形成，而形成频率较低的 3-3 键（mDAP-mDAP）则由 L,D-转肽酶催化。在这项研究中，我们发现指数生长期大肠杆菌在冷休克时 3-3 交联的频率增加，这种增加是由 L,D-转肽酶 LdtD 介导的。我们发现，一种冷诱导 RNA 解旋酶 DeaD 通过促进其翻译来增强细胞内 LdtD 水平，从而导致冷休克时 3-3 交联的丰度增加。然而，DeaD 也需要在环境温度下生长时最佳表达 LdtD。总的来说，我们的研究发现大肠杆菌在冷休克时通过改变 3-3 交联的频率来重塑 PG，这表明这些修饰在赋予在不同环境条件下生长的细菌适应性和生存优势方面发挥作用。大多数细菌都被一种称为肽聚糖 (PG) 的保护性外壳包围，这是一种广泛交联的网格状大分子。在细菌中，如大肠杆菌，PG 中的交联有两种类型：主要部分是 4-3 型，而次要部分是 3-3 型。在这里，我们发现暴露于冷休克的大肠杆菌由于一种酶 LdtD 的上调而具有更高水平的 3-3 交联，该酶催化其形成。我们发现，一种冷诱导 RNA 解旋酶 DeaD 通过促进其翻译来增强细胞内 LdtD 水平，导致冷休克时 3-3 交联增加。我们的结果表明，PG 重塑有助于在冷应激条件下生长的细菌的存活和适应性。
