Bacteriophage antidefense genes that neutralize TIR and STING immune responses.

Programmed cell suicide of infected bacteria, known as abortive infection (Abi), serves as an immune defense strategy to prevent the propagation of bacteriophage viruses. Many Abi systems utilize bespoke cyclic nucleotide immune messengers generated upon infection to mobilize cognate death effectors. Here, we identify a family of bacteriophage nucleotidyltransferases (NTases) that synthesize competitor cyclic dinucleotide (CDN) ligands and inhibit TIR NADase effectors activated via a linked STING CDN sensor domain (TIR-STING). Through a functional screen of NTase-adjacent phage genes, we uncover candidate inhibitors of cell suicide induced by heterologous expression of tonically active TIR-STING. Among these, we demonstrate that a virus MazG-like nucleotide pyrophosphohydrolase, Atd1, depletes the starvation alarmone (p)ppGpp, revealing a potential role for the alarmone-activated host toxin MazF as an executioner of TIR-driven Abi. Phage NTases and counterdefenses like Atd1 preserve host viability to ensure virus propagation and represent tools to modulate TIR and STING immune responses.

De novo determination of mosquitocidal Cry11Aa and Cry11Ba structures from naturally-occurring nanocrystals.

Cry11Aa and Cry11Ba are the two most potent toxins produced by mosquitocidal Bacillus thuringiensis subsp. israelensis and jegathesan, respectively. The toxins naturally crystallize within the host; however, the crystals are too small for structure determination at synchrotron sources. Therefore, we applied serial femtosecond crystallography at X-ray free electron lasers to in vivo-grown nanocrystals of these toxins. The structure of Cry11Aa was determined de novo using the single-wavelength anomalous dispersion method, which in turn enabled the determination of the Cry11Ba structure by molecular replacement. The two structures reveal a new pattern for in vivo crystallization of Cry toxins, whereby each of their three domains packs with a symmetrically identical domain, and a cleavable crystal packing motif is located within the protoxin rather than at the termini. The diversity of in vivo crystallization patterns suggests explanations for their varied levels of toxicity and rational approaches to improve these toxins for mosquito control.

Hydra-Elastin-like Polypeptides Increase Rapamycin Potency When Targeting Cell Surface GRP78.

Rapalogues are powerful therapeutic modalities for breast cancer; however, they suffer from low solubility and dose-limiting side effects. To overcome these challenges, we developed a long-circulating multiheaded drug carrier called 5FA, which contains rapamycin-binding domains linked with elastin-like polypeptides (ELPs). To target these "Hydra-ELPs" toward breast cancer, we here linked 5FA with four distinct peptides which are reported to engage the cell surface form of the 78 kDa glucose-regulated protein (csGRP78). To determine if these peptides affected the carrier solubility, this library was characterized by light scattering and mass spectrometry. To guide in vitro selection of the most potent functional carrier for rapamycin, its uptake and inhibition of mTORC1 were monitored in a ductal breast cancer model (BT474). Using flow cytometry to track cellular association, it was found that only the targeted carriers enhanced cellular uptake and were susceptible to proteolysis by SubA, which specifically targets csGRP78. The functional inhibition of mTOR was monitored by Western blot for pS6K, whereby the best carrier L-5FA reduced mTOR activity by 3-fold compared to 5FA or free rapamycin. L-5FA was further visualized using super-resolution confocal laser scanning microscopy, which revealed that targeting increased exposure to the carrier by ∼8-fold. This study demonstrates how peptide ligands for GRP78, such as the L peptide (RLLDTNRPLLPY), may be incorporated into protein-based drug carriers to enhance targeting.