C-Terminal Arginine-Selective Cleavage of Peptides as a Method for Mimicking Carboxypeptidase B.

C-Terminal residues play a pivotal role in dictating the structure and functions of proteins. Herein, we report a mild, efficient, chemoselective, and site-selective chemical method that allows for precise chemical proteolysis at C-terminal arginine dictated by 9,10-phenanthrenequinone independent of the remaining sequence. This biomimetic approach also exhibits the potential to synthesize C-terminal methyl ester (-CO2Me) peptides.

Interpretation of serum pancreatic enzymes in pancreatic and nonpancreatic conditions.

PURPOSE OF REVIEW: Serum levels of amylase and lipase can be elevated in nonpancreatic conditions that may or may not be associated with abdominal pain. This leads to a large proportion of patients being falsely labeled as having acute pancreatitis. In this review, we aim to summarize the existing evidence on pancreatic enzyme elevation in various pancreatic and nonpancreatic conditions and its practical implications in clinical practice and healthcare. RECENT FINDINGS: Serum amylase and lipase levels are not specific for pancreatitis. Attempts have been made to validate newer biomarkers including pancreatic elastase, serum trypsin, urinary trypsinogen-activated peptide, phospholipase A2, carboxypeptidase B, activated peptide of carboxypeptidase B, the trypsin 2 alpha 1 activation complex, and circulating cell-free DNA for the diagnosis of acute pancreatitis. SUMMARY: Serum lipase levels can be elevated in many intra-abdominal inflammatory conditions. Although more sensitive and specific than amylase, serum lipase levels are not sufficient to diagnose acute pancreatitis in patients with abdominal pain. There is a need to increase stress on radiological evidence as well increase cut-off levels of enzyme elevation for a more accurate diagnosis of acute pancreatitis.

Limited proteolysis by a prostatic endopeptidase, the sperm-activating factor initiatorin, regulates the activation of pro-carboxypeptidase B in the seminal fluid of the silkworm, Bombyx mori.

A prostate trypsin-like serine endopeptidase called initiatorin (BmIni) is an essential factor in triggering the sperm maturation response of the silkworm, Bombyx mori. BmIni has been predicted to specifically cleave the carboxyl side of two consecutive arginine residues present in certain seminal plasma and sperm proteins, but the actual substrates are still unknown. In an attempt to elucidate the molecular mechanism underlying the sperm maturation signaling pathway, in this study, we examined whether BmIni activates the seminal carboxypeptidase B (BmCPB) protein through specific degradation. First, we confirmed in vitro that the inactive BmCPB present in unmated male vesicula (v.) seminalis is activated by treatment with BmIni or trypsin. Molecular cloning of the gene encoding the seminal BmCPB protein has shown that BmCPB is produced as a secreted proenzyme and may be activated after a trypsin-like protease cleaves the boundary between the prodomain and the enzyme site. In support of these findings, both trypsin and BmIni significantly activated recombinant Pro-BmCPB, which was successfully expressed and purified as a proenzyme in Escherichia coli; moreover, two specific cleavage forms appeared in the activation by BmIni that did not appear in that by trypsin. Therefore, a recombinant protein with a mutated diarginine motif (Arg109-Arg110), which is presumed to be a pre-cleavage site of BmCPB based on its high homology with bovine CPB, was prepared and treated with BmIni. As a result, the two specific degraded peptides were no longer observed, and simultaneously the activation was suppressed. Taken together, these findings lead to the conclusion that zymogen BmCPB, which is synthesized and secreted in male reproductive organs, is activated by sequence-dependent proteolysis by BmIni during ejaculation and in the female reproductive organs, providing a clue to the mechanism underlying seminal plasma and/or sperm protein degradation by BmIni in the sperm maturation cascade of B. mori.

Malaria Box Compounds against Anopheles gambiae (Diptera: Culicidae) Carboxypeptidase B Activity to Block Malaria Transmission.

Carboxypeptidase B (CPB) plays an important role in blood digestion in mosquitos, aiding the release of free amino acids. Anopheles CPB is a target to block malaria transmission because it facilitates Plasmodium invasion of the mosquito midgut. Our study aimed to discover inhibitors of Anopheles CPB to prevent Plasmodium development in the mosquito. The Anopheles gambiae cpb (Agcpb) gene without a signal sequence was cloned into the pET28b expression vector. The recombinant AgCPB protein was expressed in E. coli BL21(DE3) within inclusion bodies after induction with 0.5 mM isopropyl ß-D-1-thiogalactopyranoside at 37°C for 4 h. The protein pellet was dissolved in 6 M urea, purified by affinity chromatography, and dialyzed in reaction buffer. The refolded recombinant AgCPB could digest the hippuryl-arginine substrate similarly to that of the commercial porcine pancreas CPB. The 20 top-scoring malaria box compounds from the virtual-screening results were then chosen for an in vitro inhibition assay against AgCPB. Four of the 20 malaria box compounds could inhibit AgCPB activity. The compound MMV007591 was the most potent inhibitor with an IC50 at 0.066 µM. The results indicate that these candidate compounds may be utilized in drug development against mosquito CPB activity to curb malaria transmission.

Antibody charge variant modulation by in vitro enzymatic treatment in different Chinese hamster ovary cell cultures.

Charge variants represent a critical quality attribute that must be controlled during the development and manufacturing of monoclonal antibodies (mAb). Previously, we reported the development of a cost-effective enzymatic treatment capable of removing the C-terminal lysine from a mAb produced by a Chinese hamster ovary (CHO) GS cell line. This treatment resulted in a significant decrease in basic charge variants and a corresponding improvement in the main peak, enabling a longer cell culture production duration for titer improvement. Here, we describe this enzymatic treatment protocol in detail and demonstrate its applicability to two additional mAbs produced by distinct industrial cell lines. The simple addition of carboxypeptidase B (CpB) at a ratio of 1:10,000 (w/w) to whole cell cultures significantly improved the main peaks for both mAbs without affecting other critical quality attributes, including size exclusion chromatography impurities and N-glycans. Our results demonstrate that this in vitro CpB treatment protocol can be used as a platform strategy to improve main peak for mAbs that exhibit high levels of basic variants attributable to C-terminal lysines. An in vitro enzymatic treatment in general may be another good addition to existing in vivo CHO cell culture strategies for titer improvement and control of critical quality attributes.

Structure of Aedes aegypti procarboxypeptidase B1 and its binding with Dengue virus for controlling infection.

Metallocarboxypeptidases play critical roles in the development of mosquitoes and influence pathogen/parasite infection of the mosquito midgut. Here, we report the crystal structure of Aedes aegypti procarboxypeptidase B1 (PCPBAe1), characterized its substrate specificity and mechanism of binding to and inhibiting Dengue virus (DENV). We show that the activated PCPBAe1 (CPBAe1) hydrolyzes both Arg- and Lys-substrates, which is modulated by residues Asp251 and Ser239 Notably, these residues are conserved in CPBs across mosquito species, possibly required for efficient digestion of basic dietary residues that are necessary for mosquito reproduction and development. Importantly, we characterized the interaction between PCPBAe1 and DENV envelope (E) protein, virus-like particles, and infectious virions. We identified residues Asp18A, Glu19A, Glu85, Arg87, and Arg89 of PCPBAe1 are essential for interaction with DENV. PCPBAe1 maps to the dimeric interface of the E protein domains I/II (Lys64-Glu84, Val238-Val252, and Leu278-Leu287). Overall, our studies provide general insights into how the substrate-binding property of mosquito carboxypeptidases could be targeted to potentially control mosquito populations or proposes a mechanism by which PCPBAe1 binds to and inhibits DENV.

Endoplasmic stress-inducing variants in CPB1 and CPA1 and risk of pancreatic cancer: A case-control study and meta-analysis.

Gene variants that encode pancreatic enzymes with impaired secretion can induce pancreatic acinar endoplasmic reticulum (ER) stress, cellular injury and pancreatitis. The role of such variants in pancreatic cancer risk has received little attention. We compared the prevalence of ER stress-inducing variants in CPA1 and CPB1 in patients with pancreatic ductal adenocarcinoma (PDAC cases), enrolled in the National Familial Pancreas Tumor Registry, to their prevalence in noncancer controls in the Genome Aggregation Database (gnomAD). Variants of unknown significance were expressed and variants with reduced secretion assessed for ER stress induction. In vitro assessments were compared with software predictions of variant function. Protein variant software was used to assess variants found in only one gnomAD control ("n-of-one" variants). A meta-analysis of prior PDAC case/control studies was also performed. Of the 1385 patients with PDAC, 0.65% were found to harbor an ER stress-inducing variant in CPA1 or CPB1, compared to 0.17% of the 64 026 controls (odds ratio [OR]: 3.80 [1.92-7.51], P = .0001). ER stress-inducing variants in the CPA1 gene were identified in 4 of 1385 PDAC cases vs 77 of 64 026 gnomAD controls (OR: 2.4 [0.88-6.58], P = .087), and variants in CPB1 were detected in 5 of 1385 cases vs 33 of 64 026 controls (OR: 7.02 [2.74-18.01], P = .0001). Meta-analysis demonstrated strong associations for pancreatic cancer and ER-stress inducing variants for both CPA1 (OR: 3.65 [1.58-8.39], P < .023) and CPB1 (OR: 9.51 [3.46-26.15], P < .001). Rare variants in CPB1 and CPA1 that induce ER stress are associated with increased odds of developing pancreatic cancer.

Structure of Aedes aegypti carboxypeptidase B1-inhibitor complex uncover the disparity between mosquito and non-mosquito insect carboxypeptidase inhibition mechanism.

Metallocarboxypeptidases (MCPs) in the mosquito midgut play crucial roles in infection, as well as in mosquito dietary digestion, reproduction, and development. MCPs are also part of the digestive system of plant-feeding insects, representing key targets for inhibitor development against mosquitoes/mosquito-borne pathogens or as antifeedant molecules against plant-feeding insects. Notably, some non-mosquito insect B-type MCPs are primarily insensitive to plant protease inhibitors (PPIs) such as the potato carboxypeptidase inhibitor (PCI; MW 4 kDa), an inhibitor explored for cancer treatment and insecticide design. Here, we report the crystal structure of Aedes aegypti carboxypeptidase-B1 (CPBAe1)-PCI complex and compared the binding with that of PCI-insensitive CPBs. We show that PCI accommodation is determined by key differences in the active-site regions of MCPs. In particular, the loop regions α6-α7 (Leu242 -Ser250 ) and ß8-α8 (Pro269 -Pro280 ) of CPBAe1 are replaced by α-helices in PCI-insensitive insect Helicoverpa zea CPBHz. These α-helices protrude into the active-site pocket of CPBHz, restricting PCI insertion and rendering the enzyme insensitive. We further compared our structure with the only other PCI complex available, bovine CPA1-PCI. The potency of PCI against CPBAe1 (Ki  = 14.7 nM) is marginally less than that of bovine CPA1 (Ki  = 5 nM). Structurally, the above loop regions that accommodate PCI binding in CPBAe1 are similar to that of bovine CPA1, although observed changes in proteases residues that interact with PCI could account for the differences in affinity. Our findings suggest that PCI sensitivity is largely dictated by structural interference, which broadens our understanding of carboxypeptidase inhibition as a mosquito population/parasite control strategy.

Productivity improvement and charge variant modulation for intensified cell culture processes by adding a carboxypeptidase B (CpB) treatment step.

The goal of cell culture process intensification is to improve productivity while maintaining acceptable quality attributes. In this report, four processes, namely a conventional manufacturing Process A, and processes intensified by enriched N-1 seed (Process B), by perfusion N-1 seed (Process C), and by perfusion production (Process D) were developed for the production of a monoclonal antibody. The three intensified processes substantially improved productivity, however, the product either failed to meet the specification for charge variant species (main peak) for Process D or the production process required early harvest to meet the specification for charge variant species, Day 10 or Day 6 for Processes B and C, respectively. The lower main peak for the intensified processes was due to higher basic species resulting from higher C-terminal lysine. To resolve this product quality issue, we developed an enzyme treatment method by introducing carboxypeptidase B (CpB) to clip the C-terminal lysine, leading to significantly increased main peak and an acceptable and more homogenous product quality for all the intensified processes. Additionally, Processes B and C with CpB treatment extended bioreactor durations to Day 14 increasing titer by 38% and 108%, respectively. This simple yet effective enzyme treatment strategy could be applicable to other processes that have similar product quality issues.

Carboxypeptidase B blocks ex vivo activation of the anaphylatoxin-neutrophil extracellular trap axis in neutrophils from COVID-19 patients.

BACKGROUND: Thrombosis and coagulopathy are highly prevalent in critically ill patients with COVID-19 and increase the risk of death. Immunothrombosis has recently been demonstrated to contribute to the thrombotic events in COVID-19 patients with coagulopathy. As the primary components of immunothrombosis, neutrophil extracellular traps (NETs) could be induced by complement cascade components and other proinflammatory mediators. We aimed to explore the clinical roles of NETs and the regulation of complement on the NET formation in COVID-19. METHODS: We recruited 135 COVID-19 patients and measured plasma levels of C5, C3, cell-free DNA and myeloperoxidase (MPO)-DNA. Besides, the formation of NETs was detected by immunofluorescent staining and the cytotoxicity to vascular endothelial HUVEC cells was evaluated by CCK-8 assay. RESULTS: We found that the plasma levels of complements C3 and MPO-DNA were positively related to coagulation indicator fibrin(-ogen) degradation products (C3: r = 0.300, p = 0.005; MPO-DNA: r = 0.316, p = 0.002) in COVID-19 patients. Besides, C3 was positively related to direct bilirubin (r = 0.303, p = 0.004) and total bilirubin (r = 0.304, p = 0.005), MPO-DNA was positively related to lactate dehydrogenase (r = 0.306, p = 0.003) and creatine kinase (r = 0.308, p = 0.004). By using anti-C3a and anti-C5a antibodies, we revealed that the complement component anaphylatoxins in the plasma of COVID-19 patients strongly induced NET formation. The pathological effect of the anaphylatoxin-NET axis on the damage of vascular endothelial cells could be relieved by recombinant carboxypeptidase B (CPB), a stable homolog of enzyme CPB2 which can degrade anaphylatoxins to inactive products. CONCLUSIONS: Over-activation in anaphylatoxin-NET axis plays a pathological role in COVID-19. Early intervention in anaphylatoxins might help prevent thrombosis and disease progression in COVID-19 patients.

Pancreatic Tissue Proteomics Unveils Key Proteins, Pathways, and Networks Associated with Type 1 Diabetes.

PURPOSE: Type 1 diabetes (T1D) is characterized by autoimmune mediated self-destruction of the pancreatic islet beta cells and the resultant insulin deficiency. However, little is known about the underlying molecular pathogenesis at the pancreatic tissue level given the limited availability of clinical specimens. EXPERIMENTAL DESIGN: Quantitative proteomic studies is performed on age-matched T1D and healthy cadaveric pancreatic tissues (n = 18 each) using TMT 10plex-based isobaric labeling and BoxCar-based label-free LC-MS/MS approaches. ELISA is used to validate the differentially expressed proteins (DEPs). RESULTS: Overall, the two quantitative proteomics approaches identified 8824 proteins, of which 261 are DEPs. KEGG pathway and functional network analyses of the DEPs reveal dysregulations to pancreatic exocrine function, complement coagulation cascades, and extracellular matrix receptor interaction pathways in T1D. A selected list of the DEPs associated with pathways, subnetworks, and plasma proteome of T1D are validated using ELISA. CONCLUSIONS AND CLINICAL RELEVANCE: Integrating labeling and label-free approaches improve the confidence in quantitative profiling of pancreatic tissue proteome, which furthers the understanding of the dysregulated pathways and functional subnetworks associated with T1D pathogenesis and may aid to develop diagnostic and therapeutic strategies for T1D.

An 18O-Labeling Assisted LC-MS Method for Accurate Quantitation of Unprocessed C-Terminal Lysine in Therapeutic Monoclonal Antibodies.

Unprocessed C-terminal lysine (C-term Lys) is one of the most common causes for the formation of basic variants in therapeutic monoclonal antibodies (mAbs). Although the C-term Lys variants are routinely quantified by a LC-MS-based peptide mapping method using the relative MS responses from both C-terminal peptides (with and without Lys), this approach often leads to overestimation of Lys-containing peptide due to the intrinsic difference in ionization efficiency. Herein, we report an 18O-labeling assisted LC-MS method, which takes advantage of the carboxypeptidase B-catalyzed Lys removal and 18O-labeling to achieve improved accuracy of C-term Lys quantitation. The fidelity of this method was first demonstrated using synthetic peptide mixture standards that mimic a wide range of C-term Lys levels. Finally, the newly developed method was applied in a case study where C-term Lys variants in mAb samples manufactured from different processes were accurately quantified and compared. This new method provides a valuable solution for studies where accurate C-term Lys levels are needed to assist decision-making and root-cause investigation.

Carboxypeptidase B-Assisted Charge-Based Fractional Diagonal Chromatography for Deep Screening of C-Terminome.

The determination of protein C-termini is of great significance for protein function annotation and proteolysis research. However, the progress of C-terminomics is still far behind its counterpart, N-terminomics, because of the low reactivity of the carboxyl group. Herein, we developed a negative selection strategy, termed carboxypeptidase B-assisted charge-based fractional diagonal chromatography (CPB-ChaFRADIC), to achieve a global C-terminome analysis. The highly reactive carboxypeptidase B cleavage was utilized to reduce the charge state of non-C-terminal peptides. Together with high-performance charge-based fractional diagonal chromatography, the C-terminal peptides could be isolated. Such a strategy was applied for profiling C-termini from Escherichia coli cell lysates and 441 canonical C-termini and 510 neo-C-termini originating from proteolytic processing were identified. These findings represent 2-fold and 5.8-fold that of identified C-termini via direct analysis, respectively. Using parallel digestion with trypsin and LysC, such a strategy enabled the identification of 604 canonical C-termini and 818 neo-C-termini, representing the largest C-terminome data set of E. coli, and no deficiency in His/Lys/Arg-containing C-terminal peptides was observed. The presented CPB-ChaFRADIC strategy is therefore a highly efficient and unbiased strategy for large-scale C-terminome analysis. Furthermore, using the CPB-ChaFRADIC strategy, we identified 107 cleavage sites and 102 substrates of caspase-3 in Jurkat cells, demonstrating that the CPB-ChaFRADIC strategy shows great promise in promoting proteolysis research. Data are available via ProteomeXchange with identifier PXD018520.

Intact and middle-down CIEF of commercial therapeutic monoclonal antibody products under non-denaturing conditions.

A two-step CIEF with chemical mobilization was developed for charge profiling of the therapeutic mAb rituximab under non-denaturing separation conditions. CIEF of the intact mAb was combined with a middle-down approach analyzing Fc/2 and F(ab´)2 fragments after digest with a commercial cysteine protease (IdeS). CIEF methods were optimized separately for the intact mAb and its fragments due to their divergent pIs. Best resolution was achieved by combining Pharmalyte (PL) 8-10.5 with PL 3-10 for variants of intact rituximab and of F(ab´)2 fragments, respectively, whereas PL 6.7-7.7 in combination with PL 3-10 was used for Fc/2 variants. Charge heterogeneity in Fc/2 dominates over F(ab´)2 . In addition, a copy product of rituximab, and adalimumab were analyzed. Both mAbs contain additional alkaline C-terminal lysine variants as confirmed by digest with carboxypeptidase B. The optimized CIEF methods for intact mAb and Fc/2 were tested for their potential as platform approaches for these mAbs. The CIEF method for Fc/2 was slightly adapted in this process. The pI values for major intact mAb variants were determined by adjacent pI markers resulting in 9.29 (rituximab) and 8.42 (adalimumab). In total, seven to eight charge variants could be distinguished for intact adalimumab and rituximab, respectively.

Predictive Value of Novel Inflammation-Based Biomarkers for Pulmonary Hypertension in the Acute Exacerbation of Chronic Obstructive Pulmonary Disease.

Recently, there has been an increasing interest in the potential clinical use of several inflammatory indexes, namely, neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and systemic-immune-inflammation index (SII). This study aimed at assessing whether these markers could be early indicators of pulmonary hypertension (PH) in patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD). A total of 185 patients were enrolled in our retrospective study from January 2017 to January 2019. Receiver operating characteristic curve (ROC) and area under the curve (AUC) were used to evaluate the clinical significance of these biomarkers to predict PH in patients with AECOPD. According to the diagnostic criterion for PH by Doppler echocardiography, the patients were stratified into two groups. The study group consisted of 101 patients complicated with PH, and the control group had 84 patients. The NLR, PLR, and SII values of the PH group were significantly higher than those of the AECOPD one (p < 0.05). The blood biomarker levels were positively correlated with NT-proBNP levels, while they had no significant correlation with the estimated pulmonary arterial systolic pressure (PASP) other than PLR. NLR, PLR, and SII values were all associated with PH (p < 0.05) in the univariate analysis, but not in the multivariate analysis. The AUC of NLR used for predicting PH was 0.701 and was higher than PLR and SII. Using 4.659 as the cut-off value of NLR, the sensitivity was 81.2%, and the specificity was 59.5%. In conclusion, these simple markers may be useful in the prediction of PH in patients with AECOPD.

Molecular characterization of carboxypeptidase B-like (CPB) in Scylla paramamosain and its role in white spot syndrome virus and Vibrio alginolyticus infection.

Carboxypeptidase plays an important physiological role in the tissues and organs of animals. In this study, we cloned an entire 2316 bp carboxypeptidase B-like (CPB) sequence with a 1302 bp open reading frame encoding a 434 amino acid peptide from Scylla paramamosain. The CPB gene was expressed highly in hepatopancreas and decreased in crab hemocytes after challenges with white spot syndrome virus (WSSV) or Vibrio alginolyticus. After CPB gene knockdown using double-stranded RNA (CPB-dsRNA), the expression of JAK, STAT, C-type lectin, crustin antimicrobial peptide, Toll-like receptors, prophenoloxidase, and myosin II essential light chain-like protein were down-regulated in hemocytes at 24 h post dsRNA treatment. CPB knockdown decreases total hemocyte count in crabs indicated that CPB may negatively regulate crab hemocyte proliferation in crabs. CPB showed an inhibitory effect on hemocyte apoptosis in crabs infected with WSSV or V. alginolyticus. The phagocytosis rate of WSSV by hemocytes was increased after CPB-dsRNA treatment. After WSSV challenge, the mortality and WSSV copy number were both decreased but the rate of hemocyte apoptosis was increased in CPB-dsRNA-treated crabs. The results indicate that the antiviral activity of the crabs was enhanced when CPB was knocked down, indicating WSSV may take advantage of CPB to benefit its replication. In contrast, the absence of CPB in crabs increased mortality following the V. alginolyticus challenge. The phagocytosis rate of V. alginolyticus by hemocytes was increased after CPB-dsRNA treatment. It was revealed that CPB may play a positive role in the immune response to V. alginolyticus through increasing the phagocytosis rate of V. alginolyticus. This research further adds to our understanding of the CPB and identifies its potential role in the innate immunity of crabs.

Peptide-modified nanochannel system for carboxypeptidase B activity detection.

Carboxypeptidase B (CPB) is a protease that specifically hydrolyzes C-terminal alkaline amino acid of a peptide, which plays an important role in biological analysis. The activity and inhibition of CPB are significant for peptide sequencing and protein engineering. In this paper, a sensitive and easily-prepared nanochannel system was used to detect the activity of CPB. We assembled the peptides composing of alkaline amino acids into the nanochannels to detect the activity of CPB based on its hydrolysis characteristic. With CPB, the peptides would be cleaved, causing less blocking-effect on the ionic current through nanochannels. This system exhibited high sensitivity (detection limit of 0.01 U mL-1), wide linear range (0.01-10 U mL-1), and fast response (less than 10 s) for specific CPB detection. We also used the system to detect the effect of CPB inhibitors and detect in complex actual samples. The strategy exhibits effective analytical characteristics and it can be regarded as a hopeful prospect for the rapid diagnosis of patients with pancreatitis.

Crystal structure of mutant carboxypeptidase T from Thermoactinomyces vulgaris with an implanted S1' subsite from pancreatic carboxypeptidase B.

A site-directed mutagenesis method has been used to obtain the G215S/A251G/T257A/D260G/T262D mutant of carboxypeptidase T from Thermoactinomyces vulgaris (CPT), in which the amino-acid residues of the S1' subsite are substituted by the corresponding residues from pancreatic carboxypeptidase B (CPB). It was shown that the mutant enzyme retained the broad, mainly hydrophobic selectivity of wild-type CPT. The mutant containing the implanted CPB S1' subsite was crystallized and its three-dimensional structure was determined at 1.29 Šresolution by X-ray crystallography. A comparison of the three-dimensional structures of CPT, the G215S/A251G/T257A/D260G/T262D CPT mutant and CPB showed that the S1' subsite of CPT has not been distorted by the mutagenesis and adequately reproduces the structure of the CPB S1' subsite. The CPB-like mutant differs from CPB in substrate selectivity owing to differences between the two enzymes outside the S1' subsite. Moreover, the difference in substrate specificity between the enzymes was shown to be affected by residues other than those that directly contact the substrate.

Structural basis for the selective inhibition of activated thrombin-activatable fibrinolysis inhibitor (TAFIa) by a selenium-containing inhibitor with chloro-aminopyridine as a basic group.

Activated thrombin-activatable fibrinolysis inhibitor (TAFIa) is a target molecule for treating thromboembolic disorders. We previously reported that design and synthesis of compound 1 containing a selenol group and chloloaminopyridine. Compound 1 showed high inhibitory activity towards TAFIa, with a high degree of selectivity for TAFIa over carboxypeptidase N (CPN). Here we report investigation of this selectivity. To obtain co-crystal of 1/pp-CPB (a surrogate of TAFIa), we synthesized protected compound 5 as a stabilized precursor of 1. The X-ray crystal structure and docking study indicated that the Cl substituent is accommodated in the pp-CPB specific pocket whereas CPN has no identical pocket. This is important information for the design of drugs targeting TAFIa with high selectivity.