Author:

Keywords:

Science & Technology, Life Sciences & Biomedicine, Biochemistry & Molecular Biology, Cell Biology, outer membrane protein A, protein targeting, SecB, Sec system, trigger factor, ESCHERICHIA-COLI, PROTEIN EXPORT, STRUCTURAL BASIS, SIGNAL-SEQUENCE, GLOBAL ANALYSIS, PREPROTEIN, RECOGNITION, RIBOSOME, BINDING, MECHANISM, Adenosine Triphosphatases, Bacterial Proteins, Escherichia coli, Escherichia coli Proteins, Fibrinogen, Protein Binding, SEC Translocation Channels, Secretory Pathway, C16/18/008#54690356, G093519N#54971232, 0601 Biochemistry and Cell Biology, Developmental Biology, 3101 Biochemistry and cell biology

Abstract:

Bacterial secretory preproteins are translocated across the inner membrane post-translationally by the SecYEG-SecA translocase. Mature domain features and signal peptides maintain preproteins in kinetically trapped, largely soluble, folding intermediates. Some aggregation-prone preproteins require chaperones, like trigger factor (TF) and SecB, for solubility and/or targeting. TF antagonizes the contribution of SecB to secretion by an unknown molecular mechanism. We reconstituted this interaction in vitro and studied targeting and secretion of the model preprotein pro-OmpA. TF and SecB display distinct, unsuspected roles in secretion. Tightly associating TF:pro-OmpA targets the translocase at SecA, but TF prevents pro-OmpA secretion. In solution, SecB binds TF:pro-OmpA with high affinity. At the membrane, when bound to the SecA C-tail, SecB increases TF and TF:pro-OmpA affinities for the translocase and allows pro-OmpA to resume translocation. Our data reveal that TF, a main cytoplasmic folding pathway chaperone, is also a bona fide post-translational secretory chaperone that directly interacts with both SecB and the translocase to mediate regulated protein secretion. Thus, TF links the cytoplasmic folding and secretion chaperone networks.