Lactic acid bacteria (LAB) have evolved into fastidious microorganisms that require amino acids from environmental sources. Some LAB have cell envelope proteases (CEPs) that drive the proteolysis of high molecular weight proteins like casein in milk. CEP activity is typically studied using casein as the predominant substrate, even though CEPs can hydrolyze other protein sources. Plant protein hydrolysis by LAB has rarely been connected to the activity of specific CEPs. This study aims to show the activity of individual CEPs using LAB growth in a minimal growth medium supplemented with high molecular weight casein or potato proteins. Using Lactococcus cremoris MG1363 as isogenic background to express CEPs, we demonstrate that CEP activity is directly related to growth in the protein-supplemented minimal growth media. Proteolysis is analyzed based on the amino acid release, allowing a comparison of CEP activities and analysis of amino acid utilization by L. cremoris MG1363. This approach provides a basis to analyze CEP activity on plant-based protein substrates as casein alternatives and to compare activity of CEP homologs.

中文翻译：

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乳球菌细胞包膜蛋白酶使乳球菌能够在补充有植物和动物来源的高分子量蛋白质的基本生长培养基中生长

乳酸菌 (LAB) 已进化为需要环境来源氨基酸的挑剔微生物。一些 LAB 含有细胞包膜蛋白酶 (CEP)，可驱动高分子量蛋白质（如牛奶中的酪蛋白）的蛋白水解。尽管 CEP 可以水解其他蛋白质来源，但通常使用酪蛋白作为主要底物来研究 CEP 活性。LAB 的植物蛋白水解很少与特定 CEP 的活性相关。本研究旨在展示在补充有高分子量酪蛋白或马铃薯蛋白的基本生长培养基中使用 LAB 生长的单个 CEP 的活性。使用乳脂乳球菌 MG1363 作为表达 CEP 的同基因背景，我们证明 CEP 活性与补充蛋白质的基本生长培养基中的生长直接相关。根据氨基酸释放来分析蛋白水解，从而可以比较 CEP 活性并分析乳脂乳杆菌 MG1363 的氨基酸利用情况。该方法为分析作为酪蛋白替代品的植物蛋白底物的 CEP 活性以及比较 CEP 同系物的活性奠定了基础。