Structural basis for the tethered peptide activation of adhesion GPCRs.

Adhesion G-protein-coupled receptors (aGPCRs) are important for organogenesis, neurodevelopment, reproduction and other processes1-6. Many aGPCRs are activated by a conserved internal (tethered) agonist sequence known as the Stachel sequence7-12. Here, we report the cryogenic electron microscopy (cryo-EM) structures of two aGPCRs in complex with Gs: GPR133 and GPR114. The structures indicate that the Stachel sequences of both receptors assume an α-helical-bulge-ß-sheet structure and insert into a binding site formed by the transmembrane domain (TMD). A hydrophobic interaction motif (HIM) within the Stachel sequence mediates most of the intramolecular interactions with the TMD. Combined with the cryo-EM structures, biochemical characterization of the HIM motif provides insight into the cross-reactivity and selectivity of the Stachel sequences. Two interconnected mechanisms, the sensing of Stachel sequences by the conserved 'toggle switch' W6.53 and the constitution of a hydrogen-bond network formed by Q7.49/Y7.49 and the P6.47/V6.47φφG6.50 motif (φ indicates a hydrophobic residue), are important in Stachel sequence-mediated receptor activation and Gs coupling. Notably, this network stabilizes kink formation in TM helices 6 and 7 (TM6 and TM7, respectively). A common Gs-binding interface is observed between the two aGPCRs, and GPR114 has an extended TM7 that forms unique interactions with Gs. Our structures reveal the detailed mechanisms of aGPCR activation by Stachel sequences and their Gs coupling.

Structure, function and pharmacology of human itch receptor complexes.

In the clades of animals that diverged from the bony fish, a group of Mas-related G-protein-coupled receptors (MRGPRs) evolved that have an active role in itch and allergic signals1,2. As an MRGPR, MRGPRX2 is known to sense basic secretagogues (agents that promote secretion) and is involved in itch signals and eliciting pseudoallergic reactions3-6. MRGPRX2 has been targeted by drug development efforts to prevent the side effects induced by certain drugs or to treat allergic diseases. Here we report a set of cryo-electron microscopy structures of the MRGPRX2-Gi1 trimer in complex with polycationic compound 48/80 or with inflammatory peptides. The structures of the MRGPRX2-Gi1 complex exhibited shallow, solvent-exposed ligand-binding pockets. We identified key common structural features of MRGPRX2 and describe a consensus motif for peptidic allergens. Beneath the ligand-binding pocket, the unusual kink formation at transmembrane domain 6 (TM6) and the replacement of the general toggle switch from Trp6.48 to Gly6.48 (superscript annotations as per Ballesteros-Weinstein nomenclature) suggest a distinct activation process. We characterized the interfaces of MRGPRX2 and the Gi trimer, and mapped the residues associated with key single-nucleotide polymorphisms on both the ligand and G-protein interfaces of MRGPRX2. Collectively, our results provide a structural basis for the sensing of cationic allergens by MRGPRX2, potentially facilitating the rational design of therapies to prevent unwanted pseudoallergic reactions.

Structure of GDP-bound Rab7 Q67L in complex with ORP1L.

Molecular processes are orchestrated by various proteins that promote early endosomes to become late endosomes and eventually fuse with lysosomes, guaranteeing the degradation of the content. Rab7, which is localized to late endosomes, is one of the most well-known GTPases. ORP1L is recruited by Rab7 to facilitate the fusion of late endosomes and lysosomes. Here, we present the structure of GDP-bound Rab7 Q67L with ORP1L. Structural analysis, supported by biochemical and ITC binding experiments, not only provides structural insight into the interactions between the ORP1L ANK domain and Rab7 but also suggests that the GTPase activity of Rab7 does not interfere with its ORP1L-binding capacity.

Structures of the ADGRG2-Gs complex in apo and ligand-bound forms.

Adhesion G protein-coupled receptors are elusive in terms of their structural information and ligands. Here, we solved the cryogenic-electron microscopy (cryo-EM) structure of apo-ADGRG2, an essential membrane receptor for maintaining male fertility, in complex with a Gs trimer. Whereas the formations of two kinks were determinants of the active state, identification of a potential ligand-binding pocket in ADGRG2 facilitated the screening and identification of dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate and deoxycorticosterone as potential ligands of ADGRG2. The cryo-EM structures of DHEA-ADGRG2-Gs provided interaction details for DHEA within the seven transmembrane domains of ADGRG2. Collectively, our data provide a structural basis for the activation and signaling of ADGRG2, as well as characterization of steroid hormones as ADGRG2 ligands, which might be used as useful tools for further functional studies of the orphan ADGRG2.

Pseudonectria keratitis-emerging pathogenic fungi in the eye.

BACKGROUND: Infectious keratitis, a significant contributor to blindness, with fungal keratitis accounting for nearly half of cases, poses a formidable diagnostic and therapeutic challenge due to its delayed clinical presentation, prolonged culture times, and the limited availability of effective antifungal medications. Furthermore, infections caused by rare fungal strains warrant equal attention in the management of this condition. CASE PRESENTATION: A case of fungal keratitis was presented, where corneal scraping material culture yielded pink colonies. Lactophenol cotton blue staining revealed distinctive spore formation consistent with the Fusarium species. Further analysis using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) identified the causative agent as Fusarium proliferatum. However, definitive diagnosis of Pseudonectria foliicola infection was confirmed through ITS sequencing. The patient's recovery was achieved with a combination therapy of voriconazole eye drops and itraconazole systemic treatment. CONCLUSION: Pseudonectria foliicola is a plant pathogenic bacterium that has never been reported in human infections before. Therefore, ophthalmologists should consider Pseudonectria foliicola as a possible cause of fungal keratitis, as early identification and timely treatment can help improve vision in most eyes.

Structural assembly of the nucleic-acid-binding Thp3-Csn12-Sem1 complex functioning in mRNA splicing.

PCI domain proteins play important roles in post-transcriptional gene regulation. In the TREX-2 complex, PCI domain-containing Sac3 and Thp1 proteins and accessory Sem1 protein form a ternary complex required for mRNA nuclear export. In contrast, structurally related Thp3-Csn12-Sem1 complex mediates pre-mRNA splicing. In this study, we determined the structure of yeast Thp3186-470-Csn12-Sem1 ternary complex at 2.9 Å resolution. Both Thp3 and Csn12 structures have a typical PCI structural fold, characterized by a stack of α-helices capped by a C-terminal winged-helix (WH) domain. The overall structure of Thp3186-470-Csn12-Sem1 complex has an inverted V-shape with Thp3 and Csn12 forming the two sides. A fishhook-shaped Sem1 makes extensive contacts on Csn12 to stabilize its conformation. The overall structure of Thp3186-470-Csn12-Sem1 complex resembles the previously reported Sac3-Thp1-Sem1 complex, but also has significant structural differences. The C-terminal WH domains of Thp3 and Csn12 form a continuous surface to bind different forms of nucleic acids with micromolar affinity. Mutation of the basic residues in the WH domains of Thp3 and Csn12 affects nucleic acid binding in vitro and mRNA splicing in vivo. The Thp3-Csn12-Sem1 structure provides a foundation for further exploring the structural elements required for its specific recruitment to spliceosome for pre-mRNA splicing.

The two paralogous copies of the YoeB-YefM toxin-antitoxin module in Staphylococcus aureus differ in DNA binding and recognition patterns.

Toxin-antitoxin (TA) systems are ubiquitous regulatory modules for bacterial growth and cell survival following stress. YefM-YoeB, the most prevalent type II TA system, is present in a variety of bacterial species. In Staphylococcus aureus, the YefM-YoeB system exists as two independent paralogous copies. Our previous research resolved crystal structures of the two oligomeric states (heterotetramer and heterohexamer-DNA ternary complex) of the first paralog as well as the molecular mechanism of transcriptional autoregulation of this module. However, structural details reflecting molecular diversity in both paralogs have been relatively unexplored. To understand the molecular mechanism of how Sa2YoeB and Sa2YefM regulate their own transcription and how each paralog functions independently, we solved a series of crystal structures of the Sa2YoeB-Sa2YefM. Our structural and biochemical data demonstrated that both paralogous copies adopt similar mechanisms of transcriptional autoregulation. In addition, structural analysis suggested that molecular diversity between the two paralogs might be reflected in the interaction profile of YefM and YoeB and the recognition pattern of promoter DNA by YefM. Interaction analysis revealed unique conformational and activating force effected by the interface between Sa2YoeB and Sa2YefM. In addition, the recognition pattern analysis demonstrated that residues Thr7 and Tyr14 of Sa2YefM specifically recognizes the flanking sequences (G and C) of the promoter DNA. Together, these results provide the structural insights into the molecular diversity and independent function of the paralogous copies of the YoeB-YefM TA system.

Structural studies of SALL family protein zinc finger cluster domains in complex with DNA reveal preferential binding to an AATA tetranucleotide motif.

The Spalt-like 4 transcription factor (SALL4) plays an essential role in controlling the pluripotent property of embryonic stem cells via binding to AT-rich regions of genomic DNA, but structural details on this binding interaction have not been fully characterized. Here, we present crystal structures of the zinc finger cluster 4 (ZFC4) domain of SALL4 (SALL4ZFC4) bound with different dsDNAs containing a conserved AT-rich motif. In the structures, two zinc fingers of SALL4ZFC4 recognize an AATA tetranucleotide. We also solved the DNA-bound structures of SALL3ZFC4 and SALL4ZFC1. These structures illuminate a common preference for the AATA tetranucleotide shared by ZFC4 of SALL1, SALL3, and SALL4. Furthermore, our cell biology experiments demonstrate that the DNA-binding activity is essential for SALL4 function as DNA-binding defective mutants of mouse Sall4 failed to repress aberrant gene expression in Sall4-/- mESCs. Thus, these analyses provide new insights into the mechanisms of action underlying SALL family proteins in controlling cell fate via preferential targeting to AT-rich sites within genomic DNA during cell differentiation.

Structure of the platelet glycoprotein Ib receptor in complex with a novel antithrombotic agent.

Agkisacucetin, a snake C-type lectin-like protein isolated from the venom of Deinagkistrodon acutus (formerly Agkistrodon acutus), is a novel antithrombotic drug candidate in phase 2 clinical trials. Agkisacucetin specifically recognizes the platelet surface receptor glycoprotein Ib α chain (GPIbα) to block GPIb and von Willebrand factor (VWF). In this study, we solved the crystal structure of the GPIbα N-terminal domain (residues 1-305) in complex with agkisacucetin to understand their molecular recognition mechanism. The crystal structure showed that agkisacucetin primarily contacts GPIbα at the C-terminal part of the conserved leucine-rich repeat (LRR) domain (LRR-6 to LRR-8) and the previously described "ß-switch" region through the ß chain. In addition, we found that agkisacucetin α chain contacts part of the GPIbα C-terminal peptide after the LRR domain through complementary charge interactions. This C-terminal peptide plays a key role in GPIbα and thrombin recognition. Therefore, our structure revealed that agkisacucetin can sterically block the interaction between the GPIb receptor and VWF and thrombin proteins to inhibit platelet function. Our structural work provides key molecular insights into how an antithrombotic drug candidate recognizes the GPIb receptor to modulate platelet function to inhibit thrombosis.

Molecular basis for arginine C-terminal degron recognition by Cul2FEM1 E3 ligase.

Degrons are elements within protein substrates that mediate the interaction with specific degradation machineries to control proteolysis. Recently, a few classes of C-terminal degrons (C-degrons) that are recognized by dedicated cullin-RING ligases (CRLs) have been identified. Specifically, CRL2 using the related substrate adapters FEM1A/B/C was found to recognize C degrons ending with arginine (Arg/C-degron). Here, we uncover the molecular mechanism of Arg/C-degron recognition by solving a subset of structures of FEM1 proteins in complex with Arg/C-degron-bearing substrates. Our structural research, complemented by binding assays and global protein stability (GPS) analyses, demonstrates that FEM1A/C and FEM1B selectively target distinct classes of Arg/C-degrons. Overall, our study not only sheds light on the molecular mechanism underlying Arg/C-degron recognition for precise control of substrate turnover, but also provides valuable information for development of chemical probes for selectively regulating proteostasis.

PTP-MEG2 regulates quantal size and fusion pore opening through two distinct structural bases and substrates.

Tyrosine phosphorylation of secretion machinery proteins is a crucial regulatory mechanism for exocytosis. However, the participation of protein tyrosine phosphatases (PTPs) in different exocytosis stages has not been defined. Here we demonstrate that PTP-MEG2 controls multiple steps of catecholamine secretion. Biochemical and crystallographic analyses reveal key residues that govern the interaction between PTP-MEG2 and its substrate, a peptide containing the phosphorylated NSF-pY83 site, specify PTP-MEG2 substrate selectivity, and modulate the fusion of catecholamine-containing vesicles. Unexpectedly, delineation of PTP-MEG2 mutants along with the NSF binding interface reveals that PTP-MEG2 controls the fusion pore opening through NSF independent mechanisms. Utilizing bioinformatics search and biochemical and electrochemical screening approaches, we uncover that PTP-MEG2 regulates the opening and extension of the fusion pore by dephosphorylating the DYNAMIN2-pY125 and MUNC18-1-pY145 sites. Further structural and biochemical analyses confirmed the interaction of PTP-MEG2 with MUNC18-1-pY145 or DYNAMIN2-pY125 through a distinct structural basis compared with that of the NSF-pY83 site. Our studies thus provide mechanistic insights in complex exocytosis processes.

An Fc-muted bispecific antibody targeting PD-L1 and 4-1BB induces antitumor immune activity in colorectal cancer without systemic toxicity.

BACKGROUND: Resistance to immune checkpoint inhibitor (ICI) therapy narrows the efficacy of cancer immunotherapy. Although 4-1BB is a promising drug target as a costimulatory molecule of immune cells, no 4-1BB agonist has been given clinical approval because of severe liver toxicity or limited efficacy. Therefore, a safe and efficient immunostimulatory molecule is urgently needed for cancer immunotherapy. METHODS: HK010 was generated by antibody engineering, and the Fab/antigen complex structure was analyzed using crystallography. The affinity and activity of HK010 were detected by multiple in vitro bioassays, including enzyme-linked immunosorbent assay (ELISA), surface plasmon resonance (SPR), flow cytometry, and luciferase-reporter assays. Humanized mice bearing human PD-L1-expressing MC38 (MC38/hPDL1) or CT26 (CT26/hPDL1) tumor transplants were established to assess the in vivo antitumor activity of HK010. The pharmacokinetics (PK) and toxicity of HK010 were evaluated in cynomolgus monkeys. RESULTS: HK010 was generated as an Fc-muted immunoglobulin (Ig)G4 PD-L1x4-1BB bispecific antibody (BsAb) with a distinguished Fab/antigen complex structure, and maintained a high affinity for human PD-L1 (KD: 2.27 nM) and low affinity for human 4-1BB (KD: 493 nM) to achieve potent PD-1/PD-L1 blockade and appropriate 4-1BB agonism. HK010 exhibited synergistic antitumor activity by blocking the PD-1/PD-L1 signaling pathway and stimulating the 4-1BB signaling pathway simultaneously, and being strictly dependent on the PD-L1 receptor in vitro and in vivo. In particular, when the dose was decreased to 0.3 mg/kg, HK010 still showed a strong antitumor effect in a humanized mouse model bearing MC38/hPDL1 tumors. Strikingly, HK010 treatment enhanced antitumor immunity and induced durable antigen-specific immune memory to prevent rechallenged tumor growth by recruiting CD8+ T cells and other lymphocytes into tumor tissue and activating tumor-infiltrating lymphocytes. Moreover, HK010 not only did not induce nonspecific production of proinflammatory cytokines but was also observed to be well tolerated in cynomolgus monkeys in 5 week repeated-dose (5, 15, or 50 mg/kg) and single-dose (75 or 150 mg/kg) toxicity studies. CONCLUSION: We generated an Fc-muted anti-PD-L1x4-1BB BsAb, HK010, with a distinguished structural interaction with PD-L1 and 4-1BB that exhibits a synergistic antitumor effect by blocking the PD-1/PD-L1 signaling pathway and stimulating the 4-1BB signaling pathway simultaneously. It is strictly dependent on the PD-L1 receptor with no systemic toxicity, which may offer a new option for cancer immunotherapy.

Structural basis for METTL6-mediated m3C RNA methylation.

RNA modifications play important roles in mediating the biological functions of RNAs. 3-methylcytidine (m3C), albeit less abundant, is found to exist extensively in tRNAs, rRNAs and mRNAs. Human METTL6 is a m3C methyltransferase for tRNAs, including tRNASER(UGA). We solved the structure of human METTL6 in the presence of S-adenosyl-L-methionine and found by enzyme assay that recombinant human METTL6 is active towards tRNASER(UGA). Structural analysis indicated the detailed interactions between S-adenosyl-L-methionine and METTL6, and suggested potential tRNA binding region on the surface of METTL6. The structural research, complemented by biochemistry enzyme assay, will definitely shed light on the design of potent inhibitors for METTL6 in near future.

N-Cadherin Regulates GluA1-Mediated Depressive-Like Behavior in Adolescent Female Rat Offspring following Prenatal Stress.

BACKGROUND: The incidence of depression is twice higher in women than in men, and gender differences in the prevalence rates first emerge around puberty. Prenatal stress (PS) induces gender-dependent depressive-like behavior in adolescent offspring, but the neuro-physiological mechanisms remain unclear. Our study aimed to investigate the possible neuro-physiological mechanisms of gender-dependent depressive-like behavior in PS adolescent offspring and further explored the possibility of treating depression in adolescent female rats. METHODS: The pregnant rats were exposed to restraint stress in the third trimester for 7 days. The depressive-like behavior and the expression of N-cadherin and AMPARs in the hippocampus of adolescent offspring rats were assessed. 10 mg/kg AMPAR antagonist CNQX and 10 mg/kg N-cadherin antagonist ADH-1 were intraperitoneally injected into female adolescent offspring, respectively; 0.2 µg AMPAR agonist CX546 was administered to the dentate gyrus of male adolescent offspring to determine the role of N-cadherin-AMPARs in depressive-like behavior of the offspring following PS. RESULTS: We found that PS increased N-cadherin expression, which upregulated GluA1 expression in the dentate gyrus, mediating depressive-like behavior in adolescent female rat offspring by reducing PSD-95. In addition, ADH-1 and CNQX improved depressive-like behavior in adolescent female offspring following PS. Furthermore, injection of the CX546 into the dentate gyrus induced depressive-like behavior in PS male offspring. CONCLUSION: The gender-dependent expression of N-cadherin-GluA1 pathway in adolescent offspring in the dentate gyrus was the key factor in gender differences of depressive-like behavior following PS.

Distinct oligomeric structures of the YoeB-YefM complex provide insights into the conditional cooperativity of type II toxin-antitoxin system.

YoeB-YefM, the widespread type II toxin-antitoxin (TA) module, binds to its own promoter to autoregulate its transcription: repress or induce transcription under normal or stress conditions, respectively. It remains unclear how YoeB-YefM regulates its transcription depending on the YoeB to YefM TA ratio. We find that YoeB-YefM complex from S.aureus exists as two distinct oligomeric assemblies: heterotetramer (YoeB-YefM2-YoeB) and heterohexamer (YoeB-YefM2-YefM2-YoeB) with low and high DNA-binding affinities, respectively. Structures of the heterotetramer alone and heterohexamer bound to promoter DNA reveals that YefM C-terminal domain undergoes disorder to order transition upon YoeB binding, which allosterically affects the conformation of N-terminal DNA-binding domain. At TA ratio of 1:2, unsaturated binding of YoeB to the C-terminal regions of YefM dimer forms an optimal heterohexamer for DNA binding, and two YefM dimers with N-terminal domains dock into the adjacent major grooves of DNA to specifically recognize the 5'-TTGTACAN6AGTACAA-3' palindromic sequence, resulting in transcriptional repression. In contrast, at TA ratio of 1:1, binding of two additional YoeB molecules onto the heterohexamer induces the completely ordered conformation of YefM and disassembles the heterohexamer into two heterotetramers, which are unable to bind the promoter DNA optimally due to steric clashes, hence derepresses TA operon transcription.

Structural Analysis of Ino2p/Ino4p Mutual Interactions and Their Binding Interface with Promoter DNA.

Gene expression is mediated by a series of regulatory proteins, i.e., transcription factors. Under different growth conditions, the transcriptional regulation of structural genes is associated with the recognition of specific regulatory elements (REs) in promoter DNA. The manner by which transcription factors recognize distinctive REs is a key question in structural biology. Previous research has demonstrated that Ino2p/Ino4p heterodimer is associated with the transcriptional regulation of phospholipid biosynthetic genes. Mechanistically, Ino2p/Ino4p could specifically recognize the inositol/choline-responsive element (ICRE), followed by the transcription activation of the phospholipid biosynthetic gene. While the promoter DNA sequence for Ino2p has already been characterized, the structural basis for the mutual interaction between Ino2p/Ino4p and their binding interface with promoter DNA remain relatively unexplored. Here, we have determined the crystalline structure of the Ino2pDBD/Ino4pDBD/DNA ternary complex, which highlights some residues (Ino2pHis12/Glu16/Arg20/Arg44 and Ino4pHis12/Glu16/Arg19/Arg20) associated with the sequence-specific recognition of promoter DNA. Our biochemical analysis showed that mutating these residues could completely abolish protein-DNA interaction. Despite the requirement of Ino2p and Ino4p for interprotein-DNA interaction, both proteins can still interact-even in the absence of DNA. Combined with the structural analysis, our in vitro binding analysis demonstrated that residues (Arg35, Asn65, and Gln69 of Ino2pDBD and Leu59 of Ino4pDBD) are critical for interprotein interactions. Together, these results have led to the conclusion that these residues are critical to establishing interprotein-DNA and protein-DNA mutual interactions.

Structural basis for RNA 3'-end recognition by the PIWIL2 PAZ domain.

PIWI family proteins are important members of Argonaute family that play an essential role in spermatogenesis and development when loaded with piRNAs. Here we solved the crystal structure of the human PIWIL2 PAZ domain and found its PAZ domain adopts a canonical PAZ fold. We furhter built a homology model of PIWIL2 bound to 2 nt 3' overhangs. We found that PIWIL2 utilizes a deep hydrophobic concave to accommodate the 2 nt at 3'-end of RNAs. The recognition of 2 nt 3' overhangs by PIWIL2 is conserved in other human PIWIL proteins, implicating the evolutionarily conserved role of PAZ domain in binding to target RNAs.

Structural insights into SMCR8 C-degron recognition by FEM1B.

C-degrons play critical roles in targeting the receptor proteins of Cullin-RING E3 ligase complexes to initiate protein degradation. FEM1 proteins, including FEM1A, FEM1B, and FEM1C, act as the receptors to specifically recognize Arg/C-degrons to enable CRL2-mediated protein turnover. Very few substrates have been identified for FEM1B, except CDK5R1. We found that CRL2FEM1B also recognizes the C-degron of an SMCR8 isoform, and uncovered the recognition of SMCR8 by FEM1B through presenting the structure of FEM1B bound to SMCR8. Our work provides insights into the role of CRL2FEM1B in regulating the lifetime of SMCR8, a critical autophagy regulator.

Sex-dependent expression of N-cadherin-GluA1 pathway-related molecules in the prefrontal cortex mediates anxiety-like behavior in male offspring following prenatal stress.

Prenatal stress (PS) affects neurodevelopment and increases the risk for anxiety in adolescence in male offspring, but the mechanism is still unclear. N-Cadherin regulates the expression of AMPA receptors (AMPARs), which mediate anxiety by modulating network excitability in the prefrontal cortex (PFC). Our results revealed that in adolescent male, but not female, offspring rats, PS induced anxiety-like behavior, as assessed by the open field test (OFT). Furthermore, N-cadherin and AMPAR subunit GluA1 were colocalized in the PFC, and the expression of the N-cadherin and the GluA1 decreased following PS exposure in male offspring rats. We also found that the AMPAR agonist CX546 did not alleviate anxiety-like behavior in adolescent male offspring rats; however, it increased the expression of GluA1 in the PFC but did not alter the expression of N-cadherin. In conclusion, our study suggested that the N-cadherin-GluA1 pathway in the PFC mediates anxiety-like behavior in adolescent male offspring rats and that N-cadherin might be required for sex differences in the effect of PS on adolescent offspring.

Structural insight into HEMK2-TRMT112-mediated glutamine methylation.

Post-translational modifications play important roles in mediating protein functions in a wide variety of cellular events in vivo. HEMK2-TRMT112 heterodimer has been reported to be responsible for both histone lysine methylation and eukaryotic release factor 1 (eRF1) glutamine methylation. However, how HEMK2-TRMT112 complex recognizes and catalyzes eRF1 glutamine methylation is largely unknown. Here, we present two structures of HEMK2-TRMT112, with one bound to SAM and the other bound with SAH and methylglutamine (Qme). Structural analyses of the post-catalytic complex, complemented by mass spectrometry experiments, indicate that the HEMK2 utilizes a specific pocket to accommodate the substrate glutamine and catalyzes the subsequent methylation. Therefore, our work not only throws light on the protein glutamine methylation mechanism, but also reveals the dual activity of HEMK2 by catalyzing the methylation of both Lys and Gln residues.