期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：27
页码：8290-8295
DOI：10.1073/pnas.1506538112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceProteolytic enzymes are inhibited in vivo by protein inhibitors. Such inhibitors are used by symbiotic bacteria in our gut to protect themselves from digestive peptidases. This is the case for Escherichia coli, which has acquired a large, multidomain inhibitor of broad inhibitory spectrum [Escherichia coli 2-macroglobulin (ECAM)]. We studied ECAM and found it is cleaved by host peptidases, which triggers large conformational rearrangement of the inhibitor--shown by protein crystallography and electron microscopy reconstructions--as well as covalent binding of the peptidase. The latter is blocked similarly to a mouse by a snap trap, which prevents damage to the bacterial envelope. Prey peptidases, however, can still be active in the digestion of intake proteins. The survival of commensal bacteria requires them to evade host peptidases. Gram-negative bacteria from the human gut microbiome encode a relative of the human endopeptidase inhibitor, 2-macroglobulin (2M). Escherichia coli 2M (ECAM) is a [~]180-kDa multidomain membrane-anchored pan-peptidase inhibitor, which is cleaved by host endopeptidases in an accessible bait region. Structural studies by electron microscopy and crystallography reveal that this cleavage causes major structural rearrangement of more than half the 13-domain structure from a native to a compact induced form. It also exposes a reactive thioester bond, which covalently traps the peptidase. Subsequently, peptidase-laden ECAM is shed from the membrane and may dimerize. Trapped peptidases are still active except against very large substrates, so inhibition potentially prevents damage of large cell envelope components, but not host digestion. Mechanistically, these results document a novel monomeric "snap trap."
