Mechanism of the prokaryotic transmembrane disulfide reduction pathway and its in vitro reconstitution from purified components

A Novel Immunomodulator Delivery Platform Based on Bacterial Biomimetic Vesicles for Enhanced Antitumor Immunity

T cell activation-induced cell death (AICD) during tumor pathogenesis is a tumor immune escape process dependent on dendritic cells (DCs). Proper immune-modulatory therapies effectively inhibit tumor-specific CD8+ T cell exhaustion and enhance antitumor immune responses. Here, high-pressure homogenization is utilized to drive immunomodulator IL10-modified bacteria to extrude through the gap and self-assemble into bacterial biomimetic vesicles exposing IL10 (IL10-BBVs) on the surface with high efficiency. IL10-BBVs efficiently target DCs in tumor-draining lymph nodes and thus increase the interaction between IL10 on BBVs and IL10R on DCs to suppress AICD and mitigate CD8+ T cell exhaustion specific to tumor antigens. Two subcutaneous peripheral injections of IL10-BBVs 1 week apart in tumor-bearing mice effectively increase systemic and intratumoral proportions of CD8+ T cells to suppress tumor growth and metastasis. Tumor-specific antigen E7 is enclosed into the periplasm of IL10-BBVs (IL10-E7-BBVs) to realize concurrent actions of the immunomodulator IL10 and the tumor antigen human papillomavirus (HPV) 16E7 in lymph nodes, further enhancing the antitumor effects mediated by CD8+ T cells. The development of this modified BBV delivery platform will expand the application of bacterial membranes and provide novel immunotherapeutic strategies for tumor treatment.

Solution structure and elevator mechanism of the membrane electron transporter CcdA

Membrane oxidoredutase CcdA plays a central role in supplying reducing equivalents from the bacterial cytoplasm to the envelope. It transports electrons across the membrane using a single pair of cysteines by a mechanism which has not been elucidated. Here we report an NMR structure of the Thermus thermophilus CcdA (TtCcdA) in an oxidized and outward-facing state. CcdA consists of two inverted structural repeats of three transmembrane helices (2 × 3-TM). We computationally modeled and experimentally validated an inward-facing state, which suggests that CcdA uses an elevator-type movement to shuttle the reactive cysteines across the membrane. CcdA belongs to the LysE superfamily. Its structure may be relevant to other LysE clan transporters. Structure comparisons of CcdA, semiSWEET, Pnu, and major facilitator superfamily (MFS) transporters provide insights about membrane transporter architecture and mechanism.

Structure and multistate function of the transmembrane electron transporter CcdA

The mechanism by which transmembrane reductases use a single pair of cysteine residues to relay electrons between protein substrates across biological membranes is a long-standing mystery in thiol-redox biochemistry. Here we show the NMR structure of a reduced-state mimic of archaeal CcdA, a protein that transfers electrons across the inner membrane, by using a redox-active NMR sample. The two cysteine positions in CcdA are separated by 20 Å. Whereas one is accessible to the cytoplasm, the other resides in the protein core, thus implying that conformational exchange is required for periplasmic accessibility. In vivo mixed disulfide-trapping experiments validated the functional positioning of the cysteines, and in vitro accessibility results confirmed conformational exchange. Our NMR and functional data together show the existence of multiple conformational states and suggest a four-state model for relaying electrons from cytosolic to periplasmic redox substrates.