Bacteria are encapsulated by a peptidoglycan cell wall that is essential for their survival¹. During cell wall assembly, a lipid-linked disaccharide–peptide precursor called lipid II is polymerized and cross-linked to produce mature peptidoglycan. As lipid II is polymerized, nascent polymers remain membrane-anchored at one end, and the other end becomes cross-linked to the matrix^2,3,4. How bacteria release newly synthesized peptidoglycan strands from the membrane to complete the synthesis of mature peptidoglycan is a long-standing question. Here, we show that a Staphylococcus aureus cell wall hydrolase and a membrane protein that contains eight transmembrane helices form a complex that may function as a peptidoglycan release factor. The complex cleaves nascent peptidoglycan internally to produce free oligomers as well as lipid-linked oligomers that can undergo further elongation. The polytopic membrane protein, which is similar to a eukaryotic CAAX protease, controls the length of these products. A structure of the complex at a resolution of 2.6 Å shows that the membrane protein scaffolds the hydrolase to orient its active site for cleaving the glycan strand. We propose that this complex functions to detach newly synthesized peptidoglycan polymer from the cell membrane to complete integration into the cell wall matrix.

细菌被肽聚糖细胞壁包裹，这对它们的生存至关重要¹。在细胞壁组装过程中，称为脂质 II 的脂质连接的二糖-肽前体被聚合和交联以产生成熟的肽聚糖。随着脂质 II 的聚合，新生聚合物在一端保持膜锚定，另一端与基质^2,3,4交联。细菌如何从膜上释放新合成的肽聚糖链以完成成熟肽聚糖的合成是一个长期存在的问题。在这里，我们展示了金黄色葡萄球菌细胞壁水解酶和包含八个跨膜螺旋的膜蛋白形成复合物，可作为肽聚糖释放因子发挥作用。该复合物在内部切割新生肽聚糖以产生游离寡聚体以及可以进一步延伸的脂质连接寡聚体。类似于真核 CAAX 蛋白酶的多面体膜蛋白控制这些产物的长度。分辨率为 2.6 Å 的复合物结构表明，膜蛋白支撑水解酶以定向其活性位点以切割聚糖链。我们提出这种复合物的功能是将新合成的肽聚糖聚合物从细胞膜上分离出来，以完全整合到细胞壁基质中。