School of Dentistry and Medical Sciences, Charles Sturt University, Boorooma Street, Wagga Wagga, NSW 2678, Australia.
Deparment of Chemistry and Biochemistry, San Francisco State University, San Francisco, CA 94132, USA.
Cells. 2023 Jul 12;12(14):1829. doi: 10.3390/cells12141829.
Polyamines are simple yet critical molecules with diverse roles in numerous pathogenic and non-pathogenic organisms. Regulating polyamine concentrations affects the transcription and translation of genes and proteins important for cell growth, stress, and toxicity. One way polyamine concentrations are maintained within the cell is via spermidine/spermine -acetyltransferases (SSATs) that acetylate intracellular polyamines so they can be exported. The bacterial SpeG enzyme is an SSAT that exhibits a unique dodecameric structure and allosteric site compared to other SSATs that have been previously characterized. While its overall 3D structure is conserved, its presence and role in different bacterial pathogens are inconsistent. For example, not all bacteria have encoded in their genomes; in some bacteria, the gene is present but has become silenced, and in other bacteria, it has been acquired on mobile genetic elements. The latter is the case for methicillin-resistant (MRSA) USA300, where it appears to aid pathogenesis. To gain a greater understanding of the structure/function relationship of SpeG from the MRSA USA300 strain (SaSpeG), we determined its X-ray crystal structure in the presence and absence of spermine. Additionally, we showed the oligomeric state of SaSpeG is dynamic, and its homogeneity is affected by polyamines and AcCoA. Enzyme kinetic assays showed that pre-incubation with polyamines significantly affected the positive cooperativity toward spermine and spermidine and the catalytic efficiency of the enzyme. Furthermore, we showed bacterial SpeG enzymes do not have equivalent capabilities to acetylate aminopropyl versus aminbutyl ends of spermidine. Overall, this study provides new insight that will assist in understanding the SpeG enzyme and its role in pathogenic and non-pathogenic bacteria at a molecular level.
多胺是一类简单但至关重要的分子，在许多病原和非病原生物中具有多种作用。调节多胺浓度会影响细胞生长、应激和毒性相关的基因和蛋白的转录和翻译。细胞内多胺浓度维持的一种方式是通过将细胞内多胺乙酰化，使其能够被输出，从而实现多胺的再循环。这种乙酰化作用是由精脒/精胺-N1-乙酰转移酶（SSAT）完成的。与其他已被鉴定的 SSAT 相比，细菌 SpeG 酶是一种具有独特十二聚体结构和别构位点的 SSAT。尽管其整体 3D 结构是保守的，但它在不同细菌病原体中的存在和作用并不一致。例如，并非所有细菌的基因组中都编码了 SpeG 酶；在一些细菌中，SpeG 基因存在但被沉默，而在其他细菌中，SpeG 基因则通过移动遗传元件获得。耐甲氧西林金黄色葡萄球菌（MRSA）USA300 就是这种情况，它似乎有助于发病机制。为了更深入地了解来自 USA300 型耐甲氧西林金黄色葡萄球菌（SaSpeG）的 SpeG 结构/功能关系，我们在有无精脒的情况下测定了其 X 射线晶体结构。此外，我们还展示了 SaSpeG 的寡聚状态是动态的，其均一性受到多胺和 AcCoA 的影响。酶动力学分析表明，多胺的预孵育显著影响了酶对精脒和精胺的正协同作用以及酶的催化效率。此外，我们还表明细菌 SpeG 酶不具有将精胺的氨基丙基端和氨基丁基端乙酰化的等效能力。总的来说，这项研究提供了新的见解，有助于从分子水平上理解 SpeG 酶及其在病原和非病原细菌中的作用。
