Rac1-bound structure and mutagenesis of the ELMO1-DOCK5 complex provide insights into how ELMO modulates DOCK activity.

Cell-free protein synthesis is useful for synthesizing difficult targets. The site-specific incorporation of non-natural amino acids into proteins is a powerful protein engineering method. In this study, we optimized the protocol for cell extract preparation from the Escherichia coli strain RFzero-iy, which is engineered to lack release factor 1 (RF-1). The BL21(DE3)-based RFzero-iy strain exhibited quite high cell-free protein productivity, and thus we established the protocols for its cell culture and extract preparation. In the presence of 3-iodo-l-tyrosine (IY), cell-free protein synthesis using the RFzero-iy-based S30 extract translated the UAG codon to IY at various sites with a high translation efficiency of >90%. In the absence of IY, the RFzero-iy-based cell-free system did not translate UAG to any amino acid, leaving UAG unassigned. Actually, UAG was readily reassigned to various non-natural amino acids, by supplementing them with their specific aminoacyl-tRNA synthetase variants (and their specific tRNAs) into the system. The high incorporation rate of our RFzero-iy-based cell-free system enables the incorporation of a variety of non-natural amino acids into multiple sites of proteins. The present strategy to create the RFzero strain is rapid, and thus promising for RF-1 deletions of various E. coli strains genomically engineered for specific requirements.

The N (1)-methyladenosine residue at position 58 of tRNA is found in the three domains of life, and contributes to the stability of the three-dimensional L-shaped tRNA structure. In thermophilic bacteria, this modification is important for thermal adaptation, and is catalyzed by the tRNA m(1)A58 methyltransferase TrmI, using S-adenosyl-L-methionine (AdoMet) as the methyl donor. We present the 2.2 Å crystal structure of TrmI from the extremely thermophilic bacterium Aquifex aeolicus, in complex with AdoMet. There are four molecules per asymmetric unit, and they form a tetramer. Based on a comparison of the AdoMet binding mode of A. aeolicus TrmI to those of the Thermus thermophilus and Pyrococcus abyssi TrmIs, we discuss their similarities and differences. Although the binding modes to the N6 amino group of the adenine moiety of AdoMet are similar, using the side chains of acidic residues as well as hydrogen bonds, the positions of the amino acid residues involved in binding are diverse among the TrmIs from A. aeolicus, T. thermophilus, and P. abyssi.

Chimeric antigen receptor (CAR)-T cell therapy has transformed the treatment of B-cell malignancies, but its success in acute myeloid leukemia (AML) remains limited. Durable responses depend on the formation of long-lived memory T cells, whereas T cell exhaustion contributes to non-response and relapse. In patients with AML who achieved remission after cord blood transplantation, we here first observe enrichment of memory T cells with high expression of the chemokine receptor CXCR4. Next, we show that engineering CAR-T cells to co-express CXCR4 enhances their persistence and anti-leukemic activity in patient-derived xenograft models. Using single-cell profiling and metabolic analysis, we find that CXCR4 promotes memory-associated transcriptional programs, reduces exhaustion, and supports oxidative metabolism. These effects are observed with CAR-T cells targeting CD25 or CD96 as AML-associated targets. Our results indicate that CXCR4 strengthens CAR-T cell memory and durability, offering a strategy to improve immunotherapy outcomes in AML and beyond.

Genetically encoded caged amino acids can be used to control the dynamics of protein activities and cellular localization in response to external cues. In the present study, we revealed the structural basis for the recognition of O-(2-nitrobenzyl)-L-tyrosine (oNBTyr) by its specific variant of Methanocaldococcus jannaschii tyrosyl-tRNA synthetase (oNBTyrRS), and then demonstrated its potential availability for time-resolved X-ray crystallography. The substrate-bound crystal structure of oNBTyrRS at a 2.79 Å resolution indicated that the replacement of tyrosine and leucine at positions 32 and 65 by glycine (Tyr32Gly and Leu65Gly, respectively) and Asp158Ser created sufficient space for entry of the bulky substitute into the amino acid binding pocket, while Glu in place of Leu162 formed a hydrogen bond with the nitro moiety of oNBTyr. We also produced an oNBTyr-containing lysozyme through a cell-free protein synthesis system derived from the Escherichia coli B95. ΔA strain with the UAG codon reassigned to the nonnatural amino acid. Another crystallographic study of the caged protein showed that the site-specifically incorporated oNBTyr was degraded to tyrosine by light irradiation of the crystals. Thus, cell-free protein synthesis of caged proteins with oNBTyr could facilitate time-resolved structural analysis of proteins, including medically important membrane proteins.

The DOCK protein family activates Rho small GTPases through guanine nucleotide exchange factor (GEF) activity. DOCK is thought to exert its GEF activity at the plasma membrane. However, the mechanism by which DOCK activity on the plasma membrane is regulated remains unclear. Herein, we present a new conformation in which DOCK5, ELMO1, RhoG, and Rac1 are aligned on a plane and symmetrically flattened, as revealed by cryo-EM using a lipid membrane-coated grid. The major conformational change leading to this structure results from rotation of each DOCK5•ELMO1 hinge site through interactions with the membrane. Biochemical and cellular experiments indicate that conformational changes driven by acidic lipids are important for regulating the GEF activity of the DOCK5•ELMO1 complex on the plasma membrane and are essential for its downstream signalling. This approach also enables the analysis of large lipid-associated complexes, such as signalosomes, and will aid studies of membrane-dependent signalling assemblies.