Romeis T, Höltje J V
Max-Planck-Institut für Entwicklungsbiologie, Abteilung Biochemie, Tübingen, Germany.
Eur J Biochem. 1994 Sep 1;224(2):597-604. doi: 10.1111/j.1432-1033.1994.00597.x.
Penicillin-binding protein 7 (PBP7) and its proteolytic degradation product PBP8 are shown to be soluble proteins, which can be set free from whole cells of Escherichia coli by an osmotic shock. The proteins are loosely associated with the membranes and are totally released into the supernatant in the presence of 1 M NaCl. Partial purification of PBP8 was accomplished by hydroxyapatite, heparin-Sepharose and MonoS chromatography. Murein meso-diaminopimelate-D-alanine DD-endopeptidase activity was demonstrated for both PBP7 and PBP8, which specifically hydrolyse the DD-diaminopimelate-alanine bonds in high-molecular-mass murein sacculi but fail to cleave these bonds in isolated dimeric muropeptides. The enzyme is inhibited by the 'penem' beta-lactam antibiotic CGP31608 at a concentration of 0.25 micrograms/ml by 50%. Thus besides PBP4 and the mepA gene product, a third endopeptidase exists in E. coli.
青霉素结合蛋白7（PBP7）及其蛋白水解降解产物PBP8被证明是可溶性蛋白，可通过渗透休克从大肠杆菌全细胞中释放出来。这些蛋白与细胞膜松散结合，在1 M NaCl存在下完全释放到上清液中。通过羟基磷灰石、肝素-琼脂糖和MonoS色谱法对PBP8进行了部分纯化。PBP7和PBP8均表现出胞壁质中-二氨基庚二酸-D-丙氨酸DD-内肽酶活性，它们能特异性水解高分子量胞壁质囊泡中的DD-二氨基庚二酸-丙氨酸键，但不能切割分离的二聚体胞壁肽中的这些键。该酶在浓度为0.25微克/毫升时被“青霉烯”β-内酰胺抗生素CGP31608抑制50%。因此，除了PBP4和mepA基因产物外，大肠杆菌中还存在第三种内肽酶。
