RhoG facilitates a conformational transition in the guanine nucleotide exchange factor complex DOCK5/ELMO1 to an open state.

The dedicator of cytokinesis (DOCK)/engulfment and cell motility (ELMO) complex serves as a guanine nucleotide exchange factor (GEF) for the GTPase Rac. RhoG, another GTPase, activates the ELMO-DOCK-Rac pathway during engulfment and migration. Recent cryo-EM structures of the DOCK2/ELMO1 and DOCK2/ELMO1/Rac1 complexes have identified closed and open conformations that are key to understanding the autoinhibition mechanism. Nevertheless, the structural details of RhoG-mediated activation of the DOCK/ELMO complex remain elusive. Herein, we present cryo-EM structures of DOCK5/ELMO1 alone and in complex with RhoG and Rac1. The DOCK5/ELMO1 structure exhibits a closed conformation similar to that of DOCK2/ELMO1, suggesting a shared regulatory mechanism of the autoinhibitory state across DOCK-A/B subfamilies (DOCK1-5). Conversely, the RhoG/DOCK5/ELMO1/Rac1 complex adopts an open conformation that differs from that of the DOCK2/ELMO1/Rac1 complex, with RhoG binding to both ELMO1 and DOCK5. The alignment of the DOCK5 phosphatidylinositol (3,4,5)-trisphosphate binding site with the RhoG C-terminal lipidation site suggests simultaneous binding of RhoG and DOCK5/ELMO1 to the plasma membrane. Structural comparison of the apo and RhoG-bound states revealed that RhoG facilitates a closed-to-open state conformational change of DOCK5/ELMO1. Biochemical and surface plasmon resonance (SPR) assays confirm that RhoG enhances the Rac GEF activity of DOCK5/ELMO1 and increases its binding affinity for Rac1. Further analysis of structural variability underscored the conformational flexibility of the DOCK5/ELMO1/Rac1 complex core, potentially facilitating the proximity of the DOCK5 GEF domain to the plasma membrane. These findings elucidate the structural mechanism underlying the RhoG-induced allosteric activation and membrane binding of the DOCK/ELMO complex.

Autism Spectrum Disorder- and/or Intellectual Disability-Associated Semaphorin-5A Exploits the Mechanism by Which Dock5 Signalosome Molecules Control Cell Shape.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that includes autism, Asperger's syndrome, and pervasive developmental disorder. Individuals with ASD may exhibit difficulties in social interactions, communication challenges, repetitive behaviors, and restricted interests. While genetic mutations in individuals with ASD can either activate or inactivate the activities of the gene product, impacting neuronal morphogenesis and causing symptoms, the underlying mechanism remains to be fully established. Herein, for the first time, we report that genetically conserved Rac1 guanine-nucleotide exchange factor (GEF) Dock5 signalosome molecules control process elongation in the N1E-115 cell line, a model line capable of achieving neuronal morphological changes. The increased elongation phenotypes observed in ASD and intellectual disability (ID)-associated Semaphorin-5A (Sema5A) Arg676-to-Cys [p.R676C] were also mediated by Dock5 signalosome molecules. Indeed, knockdown of Dock5 using clustered regularly interspaced short palindromic repeat (CRISPR)/CasRx-based guide(g)RNA specifically recovered the mutated Sema5A-induced increase in process elongation in cells. Knockdown of Elmo2, an adaptor molecule of Dock5, also exhibited similar recovery. Comparable results were obtained when transfecting the interaction region of Dock5 with Elmo2. The activation of c-Jun N-terminal kinase (JNK), one of the primary signal transduction molecules underlying process elongation, was ameliorated by either their knockdown or transfection. These results suggest that the Dock5 signalosome comprises abnormal signaling involved in the process elongation induced by ASD- and ID-associated Sema5A. These molecules could be added to the list of potential therapeutic target molecules for abnormal neuronal morphogenesis in ASD at the molecular and cellular levels.

A macrocyclic kinase inhibitor overcomes triple resistant mutations in EGFR-positive lung cancer.

Brigatinib-based therapy was effective against osimertinib-resistant EGFR C797S mutants and is undergoing clinical studies. However, tumor relapse suggests additional resistance mutations might emerge. Here, we first demonstrated the binding mode of brigatinib to the EGFR-T790M/C797S mutant by crystal structure analysis and predicted brigatinib-resistant mutations through a cell-based assay including N-ethyl-N-nitrosourea (ENU) mutagenesis. We found that clinically reported L718 and G796 compound mutations appeared, consistent with their proximity to the binding site of brigatinib, and brigatinib-resistant quadruple mutants such as EGFR-activating mutation/T790M/C797S/L718M were resistant to all the clinically available EGFR-TKIs. BI-4020, a fourth-generation EGFR inhibitor with a macrocyclic structure, overcomes the quadruple and major EGFR-activating mutants but not the minor mutants, such as L747P or S768I. Molecular dynamics simulation revealed the binding mode and affinity between BI-4020 and EGFR mutants. This study identified potential therapeutic strategies using the new-generation macrocyclic EGFR inhibitor to overcome the emerging ultimate resistance mutants.

A small molecule iCDM-34 identified by in silico screening suppresses HBV DNA through activation of aryl hydrocarbon receptor.

IFN-alpha have been reported to suppress hepatitis B virus (HBV) cccDNA via APOBEC3 cytidine deaminase activity through interferon signaling. To develop a novel anti-HBV drug for a functional cure, we performed in silico screening of the binding compounds fitting the steric structure of the IFN-alpha-binding pocket in IFNAR2. We identified 37 compounds and named them in silico cccDNA modulator (iCDM)-1-37. We found that iCDM-34, a new small molecule with a pyrazole moiety, showed anti-HCV and anti-HBV activities. We measured the anti-HBV activity of iCDM-34 dependent on or independent of entecavir (ETV). iCDM-34 suppressed HBV DNA, pgRNA, HBsAg, and HBeAg, and also clearly exhibited additive inhibitory effects on the suppression of HBV DNA with ETV. We confirmed metabolic stability of iCDM-34 was stable in human liver microsomal fraction. Furthermore, anti-HBV activity in human hepatocyte-chimeric mice revealed that iCDM-34 was not effective as a single reagent, but when combined with ETV, it suppressed HBV DNA compared to ETV alone. Phosphoproteome and Western blotting analysis showed that iCDM-34 did not activate IFN-signaling. The transcriptome analysis of interferon-stimulated genes revealed no increase in expression, whereas downstream factors of aryl hydrocarbon receptor (AhR) showed increased levels of the expression. CDK1/2 and phospho-SAMHD1 levels decreased under iCDM-34 treatment. In addition, AhR knockdown inhibited anti-HCV activity of iCDM-34 in HCV replicon cells. These results suggest that iCDM-34 decreases the phosphorylation of SAMHD1 through CDK1/2, and suppresses HCV replicon RNA, HBV DNA, and pgRNA formation.

RhoG-Binding Domain of Elmo1 Ameliorates Excessive Process Elongation Induced by Autism Spectrum Disorder-Associated Sema5A.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that includes autism, Asperger's syndrome, and pervasive developmental disorder. ASD is characterized by poor interpersonal relationships and strong attachment. The correlations between activated or inactivated gene products, which occur as a result of genetic mutations affecting neurons in ASD patients, and ASD symptoms are now of critical concern. Here, for the first time, we describe the process in which that the respective ASD-associated mutations (Arg676-to-Cys [R676C] and Ser951-to-Cys [S951C]) of semaphorin-5A (Sema5A) localize Sema5A proteins themselves around the plasma membrane in the N1E-115 cell line, a model line that can achieve neuronal morphological differentiation. The expression of each mutated construct resulted in the promotion of excessive elongation of neurite-like processes with increased differentiation protein markers; R676C was more effective than S951C. The differentiated phenotypes were very partially neutralized by an antibody, against Plexin-B3 as the specific Sema5A receptor, suggesting that the effects of Sema5A act in an autocrine manner. R676C greatly increased the activation of c-Jun N-terminal kinase (JNK), one of the signaling molecules underlying process elongation. In contrast, the blocking of JNK signaling, by a chemical JNK inhibitor or an inhibitory construct of the interaction of RhoG with Elmo1 as JNK upstream signaling molecules, recovered the excessive process elongation. These results suggest that ASD-associated mutations of Sema5A, acting through the JNK signaling cascade, lead to excessive differentiated phenotypes, and the inhibition of JNK signaling recovers them, revealing possible therapeutic targets for recovering the potential molecular and cellular phenotypes underlying certain ASD symptoms.

Targeting Ras-binding domain of ELMO1 by computational nanobody design.

The control of cell movement through manipulation of cytoskeletal structure has therapeutic prospects notably in the development of novel anti-metastatic drugs. In this study, we determine the structure of Ras-binding domain (RBD) of ELMO1, a protein involved in cytoskeletal regulation, both alone and in complex with the activator RhoG and verify its targetability through computational nanobody design. Using our dock-and-design approach optimized with native-like initial pose selection, we obtain Nb01, a detectable binder from scratch in the first-round design. An affinity maturation step guided by structure-activity relationship at the interface generates 23 Nb01 sequence variants and 17 of them show enhanced binding to ELMO1-RBD and are modeled to form major spatial overlaps with RhoG. The best binder, Nb29, inhibited ELMO1-RBD/RhoG interaction. Molecular dynamics simulation of the flexibility of CDR2 and CDR3 of Nb29 reveal the design of stabilizing mutations at the CDR-framework junctions potentially confers the affinity enhancement.

Structural basis for the dual GTPase specificity of the DOCK10 guanine nucleotide exchange factor.

Dedicator of cytokinesis 10 (DOCK10), an evolutionarily conserved guanine nucleotide exchange factor (GEF) for Rho GTPases, has the unique specificity within the DOCK-D subfamily to activate both Cdc42 and Rac, but the structural bases for these activities remained unknown. Here we present the crystal structures of the catalytic DHR2 domain of mouse DOCK10, complexed with either Cdc42 or Rac1. The structures revealed that DOCK10DHR2 binds to Cdc42 or Rac1 by slightly changing the arrangement of its two catalytic lobes. DOCK10 also has a flexible binding pocket for the 56th GTPase residue, allowing a novel interaction with Trp56Rac1. The conserved residues in switch 1 of Cdc42 and Rac1 showed common interactions with the unique Lys-His sequence in the ß5/ß6 loop of DOCK10DHR2. However, the interaction of switch 1 in Rac1 was less stable than that of switch 1 in Cdc42, due to amino acid differences at positions 27 and 30. Structure-based mutagenesis identified the DOCK10 residues that determine the Cdc42/Rac1 dual specificity.

Structural Insight into TNIK Inhibition.

TRAF2- and NCK-interacting kinase (TNIK) has emerged as a promising therapeutic target for colorectal cancer because of its essential role in regulating the Wnt/ß-catenin signaling pathway. Colorectal cancers contain many mutations in the Wnt/ß-catenin signaling pathway genes upstream of TNIK, such as the adenomatous polyposis coli (APC) tumor suppressor gene. TNIK is a regulatory component of the transcriptional complex composed of ß-catenin and T-cell factor 4 (TCF4). Inhibition of TNIK is expected to block the aberrant Wnt/ß-catenin signaling caused by colorectal cancer mutations. Here we present structural insights into TNIK inhibitors targeting the ATP-binding site. We will discuss the effects of the binding of different chemical scaffolds of nanomolar inhibitors on the structure and function of TNIK.

Crystal structure of human acetylcholinesterase in complex with tacrine: Implications for drug discovery.

Alzheimer's disease (AD) is one of the most common, progressive neurodegenerative disorders affecting the aged populations. Though various disease pathologies have been suggested for AD, the impairment of the cholinergic system is one of the critical factors for the disease progression. Restoration of the cholinergic transmission through acetylcholinesterase (AChE) inhibitors is a promising disease modifying therapy. Being the first marketed drug for AD, tacrine reversibly inhibits AChE and thereby slows the breakdown of the chemical messenger acetylcholine (ACh) in the brain. However, the atomic level of interactions of tacrine towards human AChE (hAChE) is unknown for years. Hence, in the current study, we report the X-ray structure of hAChE-tacrine complex at 2.85 Å resolution. The conformational heterogeneity of tacrine within the electron density was addressed with the help of molecular mechanics assisted methods and the low-energy ligand configuration is reported, which provides a mechanistic explanation for the high binding affinity of tacrine towards AChE. Additionally, structural comparison of reported hAChE structures sheds light on the conformational selection and induced fit effects of various active site residues upon binding to different ligands and provides insight for future drug design campaigns against AD where AChE is a drug target.

Structural insights into the small GTPase specificity of the DOCK guanine nucleotide exchange factors.

The dedicator of cytokinesis (DOCK) family of guanine nucleotide exchange factors (GEFs) regulates cytoskeletal dynamics by activating the GTPases Rac and/or Cdc42. Eleven human DOCK proteins play various important roles in developmental processes and the immune system. Of these, DOCK1-5 proteins bind to engulfment and cell motility (ELMO) proteins to perform their physiological functions. Recent structural studies have greatly enhanced our understanding of the complex and diverse mechanisms of DOCK GEF activity and GTPase recognition and its regulation by ELMO. This review is focused on gaining structural insights into the substrate specificity of the DOCK GEFs, and discuss how Rac and Cdc42 are specifically recognized by the catalytic DHR-2 and surrounding domains of DOCK or binding partners.

Cryo-EM structure of the human ELMO1-DOCK5-Rac1 complex.

The dedicator of cytokinesis (DOCK) family of guanine nucleotide exchange factors (GEFs) promotes cell motility, phagocytosis, and cancer metastasis through activation of Rho guanosine triphosphatases. Engulfment and cell motility (ELMO) proteins are binding partners of DOCK and regulate Rac activation. Here, we report the cryo-electron microscopy structure of the active ELMO1-DOCK5 complex bound to Rac1 at 3.8-Å resolution. The C-terminal region of ELMO1, including the pleckstrin homology (PH) domain, aids in the binding of the catalytic DOCK homology region 2 (DHR-2) domain of DOCK5 to Rac1 in its nucleotide-free state. A complex α-helical scaffold between ELMO1 and DOCK5 stabilizes the binding of Rac1. Mutagenesis studies revealed that the PH domain of ELMO1 enhances the GEF activity of DOCK5 through specific interactions with Rac1. The structure provides insights into how ELMO modulates the biochemical activity of DOCK and how Rac selectivity is achieved by ELMO.

Reduced efficacy of a Src kinase inhibitor in crowded protein solution.

The inside of a cell is highly crowded with proteins and other biomolecules. How proteins express their specific functions together with many off-target proteins in crowded cellular environments is largely unknown. Here, we investigate an inhibitor binding with c-Src kinase using atomistic molecular dynamics (MD) simulations in dilute as well as crowded protein solution. The populations of the inhibitor, 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1), in bulk solution and on the surface of c-Src kinase are reduced as the concentration of crowder bovine serum albumins (BSAs) increases. This observation is consistent with the reduced PP1 inhibitor efficacy in experimental c-Src kinase assays in addition with BSAs. The crowded environment changes the major binding pathway of PP1 toward c-Src kinase compared to that in dilute solution. This change is explained based on the population shift mechanism of local conformations near the inhibitor binding site in c-Src kinase.

Direct homophilic interaction of LAMP2A with the two-domain architecture revealed by site-directed photo-crosslinks and steric hindrances in mammalian cells.

LAMP1 (lysosomal-associated membrane protein 1) and LAMP2 are the most abundant protein components of lysosome membranes. Both LAMPs have common structures consisting of a large lumenal domain composed of two domains (N-domain and C-domain, which are membrane-distal and -proximal, respectively), both with the ß-prism fold, a transmembrane domain, and a short cytoplasmic tail. LAMP2 is involved in various aspects of autophagy, and reportedly forms high-molecular weight complexes at the lysosomal membrane. We previously showed that LAMP2 molecules coimmunoprecipitated with each other, but whether the homophilic interaction is direct or indirect has remained to be elucidated. In the present study, we demonstrated the direct homophilic interaction of mouse LAMP2A molecules, using expanded genetic code technologies that generate photo-crosslinking and/or steric hindrance at specified interfaces. Specifically, the results suggested that LAMP2A molecules assemble by facing each other with one side of the ß-prism (defined as side A) of the C-domains. The N-domain truncation, which increased the coimmunoprecipitation of LAMP2A molecules in our previous study, permitted the nonspecific involvement of both sides of the ß-prism (side A and side B). Thus, the presence of the N-domain restricts the LAMP2A interactions to side A-specific. The truncation of LAMP2A impaired the recruitment of GAPDH (a CMA-substrate) fused to the HaloTag protein to the surface of late endosomes/lysosomes (LE/Lys) and affected a process that generates LE/Lys. The present study revealed that the homophilic interaction of LAMP2A is direct, and the side A-specific, homophilic interaction of LAMP2A is required for the functional aspects of LAMP2A.Abbreviations: Aloc-Lys: Nε-allyloxycarbonyl-l-lysine; CMA: chaperone-mediated autophagy; FFE: free-flow electrophoresis; GAPDH-HT: glyceraldehyde-3-phosphate dehydrogenase fused to HaloTag protein; LAMP1: lysosomal-associated membrane protein 1; LAMP2A: lysosomal-associated membrane protein 2A; LBPA: lysobisphosphatidic acid; LE/Lys: late endosome/lysosomes; MEFs: mouse embryonic fibroblasts; pBpa: p-benzoyl- l-phenylalanine.

A conserved PI(4,5)P2-binding domain is critical for immune regulatory function of DOCK8.

DOCK8 is a Cdc42-specific guanine-nucleotide exchange factor that is essential for development and functions of various subsets of leukocytes in innate and acquired immune responses. Although DOCK8 plays a critical role in spatial control of Cdc42 activity during interstitial leukocyte migration, the mechanism remains unclear. We show that the DOCK homology region (DHR)-1 domain of DOCK8 binds specifically to phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and is required for its recruitment to the plasma membrane. Structural and biochemical analyses reveal that DOCK8 DHR-1 domain consists of a C2 domain-like core with loops creating the upper surface pocket, where three basic residues are located for stereospecific recognition of phosphoinositides. Substitution of the two basic residues, K576 and R581, with alanine abolished PI(4,5)P2 binding in vitro, ablated the ability of DOCK8 to activate Cdc42 and support leukocyte migration in three-dimensional collagen gels. Dendritic cells carrying the mutation exhibited defective interstitial migration in vivo. Thus, our study uncovers a critical role of DOCK8 in coupling PI(4,5)P2 signaling with Cdc42 activation for immune regulation.

Gilteritinib overcomes lorlatinib resistance in ALK-rearranged cancer.

ALK gene rearrangement was observed in 3%-5% of non-small cell lung cancer patients, and multiple ALK-tyrosine kinase inhibitors (TKIs) have been sequentially used. Multiple ALK-TKI resistance mutations have been identified from the patients, and several compound mutations, such as I1171N + F1174I or I1171N + L1198H are resistant to all the approved ALK-TKIs. In this study, we found that gilteritinib has an inhibitory effect on ALK-TKI-resistant single mutants and I1171N compound mutants in vitro and in vivo. Surprisingly, EML4-ALK I1171N + F1174I compound mutant-expressing tumors were not completely shrunk but regrew within a short period of time after alectinib or lorlatinib treatment. However, the relapsed tumor was markedly shrunk after switching to the gilteritinib in vivo model. In addition, gilteritinib was effective against NTRK-rearranged cancers including entrectinib-resistant NTRK1 G667C-mutant and ROS1 fusion-positive cancer.

Granzyme A Stimulates pDCs to Promote Adaptive Immunity via Induction of Type I IFN.

Granzyme A (GzmA), together with perforin, are well-known for their cytotoxic activity against tumor or virus-infected cells. In addition to this cytotoxic function, GzmA stimulates several immune cell types and induces inflammation in the absence of perforin, however, its effect on the dendritic cell (DC) is unknown. In the current study, we showed that recombinant GzmA induced the phenotypic maturation of plasmacytoid DCs (pDCs) and conventional DCs (cDCs), but not their apoptosis. Particularly, GzmA made pDCs more functional, thus leading to production of type I interferon (IFN) via the TLR9-MyD88 pathway. We also demonstrated that GzmA binds TLR9 and co-localizes with it in endosomes. When co-administered with antigen, GzmA acted as a powerful adjuvant for eliciting antigen-specific cytotoxic CD8+ T lymphocytes (CTLs) that protected mice from tumor challenge. The induction of CTL was completely abolished in XCR1+ DC-depleted mice, whereas it was reduced to less than half in pDC-depleted or IFN-α/ß receptor knockout mice. Thus, CTL cross-priming was dependent on XCR1+cDC and also type I IFN, which was produced by GzmA-activated pDCs. These results indicate that GzmA -stimulated pDCs enhance the cross-priming activity of cDCs in situ. We also showed that the adjuvant effect of GzmA is superior to CpG-ODN and LPS. Our findings highlight the ability of GzmA to bridge innate and adaptive immune responses via pDC help and suggest that GzmA may be useful as a vaccine adjuvant.

Structural Basis for the Dual Substrate Specificity of DOCK7 Guanine Nucleotide Exchange Factor.

The Dedicator Of CytoKinesis (DOCK) family of atypical guanine nucleotide exchange factors activates the Rho family GTPases Rac and/or Cdc42 through DOCK homology region 2 (DHR-2). Previous structural analyses of the DHR-2 domains of DOCK2 and DOCK9 have shown that they preferentially bind Rac1 and Cdc42, respectively; however, the molecular mechanism by which DHR-2 distinguishes between these GTPases is unclear. Here we report the crystal structure of the Cdc42-bound form of the DOCK7 DHR-2 domain showing dual specificity for Rac1 and Cdc42. The structure revealed increased substrate tolerance of DOCK7 at the interfaces with switch 1 and residue 56 of Cdc42. Furthermore, molecular dynamics simulations showed a closed-to-open conformational change in the DOCK7 DHR-2 domain between the Cdc42- and Rac1-bound states by lobe B displacement. Our results suggest that lobe B acts as a sensor for identifying different switch 1 conformations and explain how DOCK7 recognizes both Rac1 and Cdc42.

Structural Basis for the Inhibition of Cyclin G-Associated Kinase by Gefitinib.

Gefitinib is the molecular target drug for advanced non-small-cell lung cancer. The primary target of gefitinib is the positive mutation of epidermal growth factor receptor, but it also inhibits cyclin G-associated kinase (GAK). To reveal the molecular bases of GAK and gefitinib binding, structure analyses were conducted and determined two forms of the gefitinib-bound nanobody⋅GAK kinase domain complex structures. The first form, GAK_1, has one gefitinib at the ATP binding pocket, whereas the second form, GAK_2, binds one each in the ATP binding site and a novel binding site adjacent to the activation segment C-terminal helix, a unique element of the Numb-associated kinase family. In the novel binding site, gefitinib binds in the hydrophobic groove around the activation segment, disrupting the conserved hydrogen bonds for the catalytic activity. These structures suggest possibilities for the development of selective GAK inhibitors for viral infections, such as the hepatitis C virus.

Cholesterol sulfate is a DOCK2 inhibitor that mediates tissue-specific immune evasion in the eye.

Although immune responses are essential to protect the body from infection, they can also harm tissues. Certain tissues and organs, including the eye, constitute specialized microenvironments that locally inhibit immune reactivity. Dedicator of cytokinesis protein 2 (DOCK2) is a Rac-specific guanine nucleotide exchange factor (GEF) that is predominantly found in hematopoietic cells. DOCK2 plays a key role in immune surveillance because it is essential for the activation and migration of leukocytes. DOCK2 mutations cause severe immunodeficiency in humans. We found that DOCK2-mediated Rac activation and leukocyte migration were effectively inhibited by cholesterol sulfate (CS), but not by cholesterol or other sulfated steroids. CS bound to the catalytic domain of DOCK2 and suppressed its GEF activity. Mass spectrometric quantification revealed that CS was most abundantly produced in the Harderian gland, which provides the lipids that form the oily layer of the tear film. Sulfation of cholesterol is mediated by the sulfotransferases SULT2B1b and, to a lesser extent, SULT2B1a, which are produced from the same gene through alternative splicing. By genetically inactivating Sult2b1, we showed that the lack of CS in mice augmented ultraviolet- and antigen-induced ocular surface inflammation, which was suppressed by administration of eye drops containing CS. Thus, CS is a naturally occurring DOCK2 inhibitor and contributes to the generation of the immunosuppressive microenvironment in the eye.

Phosphorylated and non-phosphorylated HCK kinase domains produced by cell-free protein expression.

Since phosphorylation is involved in various physiological events, kinases and interacting factors can be potential targets for drug discovery. For the development and improvement of inhibitors from the point of view of mechanistic enzymology, a cell-free protein synthesis system would be advantageous, since it could prepare mutant proteins easily. However, especially in the case of protein kinase, product solubility remains one of the major challenges. To overcome this problem, we prepared a chaperone-supplemented extract from Escherichia coli BL21 cells harboring a plasmid encoding a set of chaperone genes, dnaK, dnaJ, and grpE. We explored cell-disruption procedures and constructed an efficient protein synthesis system. Employing this system, we produced the kinase domain of human hematopoietic cell kinase (HCK) to obtain further structural information about its molecular interaction with one of its inhibitors, previously developed by our group (RK-20449). Lower reaction temperature improved the solubility, and addition of a protein phosphatase (YpoH) facilitated the homogeneous production of the non-phosphorylated kinase domain. Crystals of the purified product were obtained and the kinase-inhibitor complex structure was solved at 1.7 Šresolution. In addition, results of kinase activity measurement, using a synthetic substrate, showed that the kinase activity was facilitated by autophosphorylation at Tyr416, as confirmed by the peptide mass mapping.