Predictors for neoplastic progression in patients with Barrett's Esophagus: a prospective cohort study.

OBJECTIVES: Patients with Barrett's esophagus (BE) have an increased risk of developing esophageal adenocarcinoma (EAC). As the absolute risk remains low, there is a need for predictors of neoplastic progression to tailor more individualized surveillance programs. The aim of this study was to identify such predictors of progression to high-grade dysplasia (HGD) and EAC in patients with BE after 4 years of surveillance and to develop a prediction model based on these factors. METHODS: We included 713 patients with BE (≥ 2 cm) with no dysplasia (ND) or low-grade dysplasia (LGD) in a multicenter, prospective cohort study. Data on age, gender, body mass index (BMI), reflux symptoms, tobacco and alcohol use, medication use, upper gastrointestinal (GI) endoscopy findings, and histology were prospectively collected. As part of this study, patients with ND underwent surveillance every 2 years, whereas those with LGD were followed on a yearly basis. Log linear regression analysis was performed to identify risk factors associated with the development of HGD or EAC during surveillance. RESULTS: After 4 years of follow-up, 26/713 (3.4%) patients developed HGD or EAC, with the remaining 687 patients remaining stable with ND or LGD. Multivariable analysis showed that a known duration of BE of ≥ 10 years (risk ratio (RR) 3.2; 95% confidence interval (CI) 1.3-7.8), length of BE (RR 1.11 per cm increase in length; 95% CI 1.01-1.2), esophagitis (RR 3.5; 95% CI 1.3-9.5), and LGD (RR 9.7; 95% CI 4.4-21.5) were significant predictors of progression to HGD or EAC. In a prediction model, we found that the annual risk of developing HGD or EAC in BE varied between 0.3% and up to 40%. Patients with ND and no other risk factors had the lowest risk of developing HGD or EAC (<1%), whereas those with LGD and at least one other risk factor had the highest risk of neoplastic progression (18-40%). CONCLUSIONS: In patients with BE, the risk of developing HGD or EAC is predominantly determined by the presence of LGD, a known duration of BE of ≥10 years, longer length of BE, and presence of esophagitis. One or combinations of these risk factors are able to identify patients with a low or high risk of neoplastic progression and could therefore be used to individualize surveillance intervals in BE.

A pro-inflammatory genotype predisposes to Barrett's esophagus.

INTRODUCTION: Severity of mucosal inflammation is shown to be associated with Barrett's esophagus (BE) development in animals. It has therefore been postulated that a strong pro-inflammatory host response predisposes to BE. AIM: To determine the impact of cytokine gene polymorphisms on the development of BE. METHODS: The multiplex SNaPshot method was used to determine interleukin (IL)-12B (A+1188C), IL-10 (C-592A, C-819T, A-1082G), IL-8 (A-251T), IL-6 (G-174C) and IL-2 (G-330T) gene polymorphisms in 255 patients with BE and 247 patients with reflux esophagitis (RE). RESULTS: The presence of the IL-12B C-allele, which is associated with increased IL-12p70 expression, was more frequently observed in BE than in RE patients [odds ratio (OR) 1.8; 95% confidence interval (CI) 1.2-2.7; P = 0.007). The risk of BE was increased in patients in whom the IL-12B C-allele coincided with a hiatal hernia (OR 2.9; 95% CI 1.32-6.58; P = 0.008). The IL-10(-1082) GG genotype, which is associated with higher IL-10 levels, was also associated with a decreased risk of BE when it was associated with the IL-12B C-allele, indicating IL-10-dependent down-regulation of IL-12p70 expression. A combination of the IL-12B AA genotype and the IL-10 AA or AG genotypes was associated with RE (OR 1.4; 95% CI 1.05-1.85; P = 0.011). CONCLUSION: A genetic profile predisposing to a strong pro-inflammatory host response, mediated by IL-12p70 and partially dependent on IL-10, is associated with BE. This risk further increases when this genotype coincides with a hiatal hernia, suggesting that exposure to gastroesophageal reflux in the presence of a pro-inflammatory genetic background is a driving force in the development of BE.

The role of endorectal ultrasound in therapeutic decision-making for local vs. transabdominal resection of rectal tumors.

INTRODUCTION: In rectal tumors, preoperative biopsies frequently fail to diagnose an invasive carcinoma. Endorectal ultrasound is considered a useful adjunct in preoperative staging of rectal tumors. However, feasibility of endorectal ultrasound and its role in therapeutic decision-making in presumed rectal adenomas is sparsely studied. METHODS: Endorectal ultrasound was performed in 268 tumors referred for local excision because biopsies showed tubulovillous adenoma. Feasibility of endorectal ultrasound was studied and ultrasound staging was compared with definite histopathologic findings. RESULTS: In 231 tumors, endorectal ultrasound was technically feasible (86 percent). Median distance from the dentate line was 11 cm in nonassessable tumors and 7 cm in assessable tumors (P < 0.001). In 21 tumors, endorectal ultrasound was not conclusive, mainly in tumors being recurrent or after recent endoscopic manipulation (P < 0.001). With endorectal ultrasound the rate of preoperative missed carcinomas could be reduced from 21 to 3 percent (P < 0.01). In diagnosing tubulovillous adenomas, sensitivity and specificity of endorectal ultrasound was 89 and 86 percent, respectively. CONCLUSIONS: Endorectal ultrasound is technically feasible in almost all presumed rectal adenomas, referred for local excision. Proper endorectal ultrasound interpretation is possible in 78 percent of all presumed rectal adenomas. Endorectal ultrasound is very reliable in diagnosing tubulovillous adenomas, and therapeutic decision-making regarding local excision vs. radical surgery based on endorectal ultrasound is valid.

Flexibility and variability of TIMP binding: X-ray structure of the complex between collagenase-3/MMP-13 and TIMP-2.

The excessive activity of matrix metalloproteinases (MMPs) contributes to pathological processes such as arthritis, tumor growth and metastasis if not balanced by the tissue inhibitors of metalloproteinases (TIMPs). In arthritis, the destruction of fibrillar (type II) collagen is one of the hallmarks, with MMP-1 (collagenase-1) and MMP-13 (collagenase-3) being identified as key players in arthritic cartilage. MMP-13, furthermore, has been found in highly metastatic tumors. We have solved the 2.0 A crystal structure of the complex between the catalytic domain of human MMP-13 (cdMMP-13) and bovine TIMP-2. The overall structure resembles our previously determined MT1-MMP/TIMP-2 complex, in that the wedge-shaped TIMP-2 inserts with its edge into the entire MMP-13 active site cleft. However, the inhibitor is, according to a relative rotation of approximately 20 degrees, oriented differently relative to the proteinase. Upon TIMP binding, the catalytic zinc, the zinc-ligating side chains, the enclosing MMP loop and the S1' wall-forming segment move significantly and in concert relative to the rest of the cognate MMP, and the active site cleft constricts slightly, probably allowing a more favourable interaction between the Cys1(TIMP) alpha-amino group of the inhibitor and the catalytic zinc ion of the enzyme. Thus, this structure supports the view that the central N-terminal TIMP segment essentially defines the relative positioning of the TIMP, while the flanking edge loops determine the relative orientation, depending on the individual target MMP.

Crystal structure of the E. coli dipeptidyl carboxypeptidase Dcp: further indication of a ligand-dependent hinge movement mechanism.

Dcp from Escherichia coli is a 680 residue cytoplasmic peptidase, which shows a strict dipeptidyl carboxypeptidase activity. Although Dcp had been assigned to the angiotensin I-converting enzymes (ACE) due to blockage by typical ACE inhibitors, it is currently grouped into the M3 family of mono zinc peptidases, which also contains the endopeptidases neurolysin and thimet oligopeptidase (TOP). We have cloned, expressed, purified, and crystallized Dcp in the presence of an octapeptide "inhibitor", and have determined its 2.0A crystal structure using MAD methods. The analysis revealed that Dcp consists of two half shell-like subdomains, which enclose an almost closed two-chamber cavity. In this cavity, two dipeptide products presumably generated by Dcp cleavage of the octapeptide bind to the thermolysin-like active site fixed to side-chains, which are provided by both subdomains. In particular, an Arg side-chain backed by a Glu residue, together with two Tyr phenolic groups provide a charged anchor for fixing the C-terminal carboxylate group of the P2' residue of a bound substrate, explaining the strict dipeptidyl carboxypeptidase specificity of Dcp. Tetrapeptidic substrates are fixed only via their main-chain functions from P2 to P2', suggesting a broad residue specificity for Dcp. Both subdomains exhibit very similar chain folds as the equivalent but abducted subdomains of neurolysin and TOP. Therefore, this "product-bound" Dcp structure seems to represent the inhibitor/substrate-bound "closed" form of the M3 peptidases, generated from the free "open" substrate-accessible form by a hinge-bending mechanism. A similar mechanism has recently been demonstrated experimentally for ACE2.

The staphylocoagulase family of zymogen activator and adhesion proteins.

Staphylocoagulase (SC) secreted by Staphylococcus aureus is a potent non-proteolytic activator of the blood coagulation zymogen prothrombin and the prototype of a newly established zymogen activator and adhesion protein (ZAAP) family. The conformationally activated SC.prothrombin complex specifically cleaves fibrinogen to fibrin, which propagates the growth of bacteria-fibrin-platelet vegetations in acute bacterial endocarditis. Our recent 2.2 A X-ray crystal structures of an active SC fragment [SC(1-325)] bound to the prothrombin zymogen catalytic domain, prethrombin 2, demonstrated that SC(1-325) represents a new type of non-proteolytic activator with a unique fold. The observed insertion of the SC(1-325) N-terminus into the 'Ile 16' cleft of prethrombin 2, which triggers the activating conformational change, provided the first unambiguous structural evidence for the 'molecular sexuality' mechanism of non-proteolytic zymogen activation. Based on the SC(1-325) fold, a new family of bifunctional zymogen activator and adhesion proteins was identified that possess N-terminal domains homologous to SC(1-325) and C-terminal domains that mediate adhesion to plasma or extracellular matrix proteins. Further investigation of the ZAAP family may lead to new insights into the mechanisms of bacterial factors that hijack zymogens of the human blood coagulation and fibrinolytic systems to promote and disseminate endocarditis and other infectious diseases.

Crystal structure of the catalytic domain of MMP-16/MT3-MMP: characterization of MT-MMP specific features.

Membrane-type matrix metalloproteinases (MT-MMPs) have attracted strong attention, because four of them can activate a key player in the tumor scenario, proMMP-2/progelatinase A. In addition to this indirect effect on the cellular environment, these MT-MMPs degrade extracellular matrix proteins, and their overproduction is associated with tumor growth. We have solved the structure of the catalytic domain (cd) of MT3-MMP/MMP-16 in complex with the hydroxamic acid inhibitor batimastat. CdMT3-MMP exhibits a classical MMP-fold with similarity to MT1-MMP. Nevertheless, it also shows unique properties such as a modified MT-specific loop and a closed S1' specificity pocket, which might help to design specific inhibitors. Some MT-MMP-specific features, derived from the crystal structures of MT-1-MMP determined previously and MT3-MMP, and revealed in recent mutagenesis experiments, explain the impaired interaction of the MT-MMPs with TIMP-1. Docking experiments with proMMP-2 show some exposed loops including the MT-loop of cdMT3-MMP involved in the interaction with the proMMP-2 prodomain in the activation encounter complex. This model might help to understand the experimentally proven importance of the MT-loop for the activation of proMMP-2.

Local formalin instillation: an effective treatment for uncontrolled radiation-induced hemorrhagic proctitis.

AIM: The aim of this study was to evaluate the efficacy of local instillation of 4% formalin in the management of uncontrolled radiation-induced and ischemic hemorrhagic proctitis. PATIENTS AND METHODS: Eight patients were reviewed. Operation characteristics, morbidity and long-term results were analyzed. RESULTS: All patients were followed for a median of 18 months. In 5 patients the bleeding stopped after a single treatment and in 3 after a second one. During follow-up no recurrent rectal bleeding occurred, no further medical treatment was needed and in all patients the complaints had disappeared. CONCLUSION: Local instillation of 4% formalin is an effective treatment for uncontrolled radiation-induced and ischemic hemorrhagic proctitis.

The metabolism and excretion of galantamine in rats, dogs, and humans.

Galantamine is a competitive acetylcholine esterase inhibitor with a beneficial therapeutic effect in patients with Alzheimer's disease. The metabolism and excretion of orally administered (3)H-labeled galantamine was investigated in rats and dogs at a dose of 2.5 mg base-Eq/kg body weight and in humans at a dose of 4 mg base-Eq. Both poor and extensive metabolizers of CYP2D6 were included in the human study. Urine, feces, and plasma samples were collected for up to 96 h (rats) or 168 h (dogs and humans) after dosing. The radioactivity of the samples and the concentrations of galantamine and its major metabolites were analyzed. In all species, galantamine and its metabolites were predominantly excreted in the urine (from 60% in male rats to 93% in humans). Excretion of radioactivity was rapid and nearly complete at 96 h after dosing in all species. Major metabolic pathways were glucuronidation, O-demethylation, N-demethylation, N-oxidation, and epimerization. All metabolic pathways observed in humans occurred in at least one animal species. In extensive metabolizers for CYP2D6, urinary metabolites resulting from O-demethylation represented 33.2% of the dose compared with 5.2% in poor metabolizers, which showed correspondingly higher urinary excretion of unchanged galantamine and its N-oxide. The glucuronide of O-desmethyl-galantamine represented up to 19% of the plasma radioactivity in extensive metabolizers but could not be detected in poor metabolizers. Nonvolatile radioactivity and unchanged galantamine plasma kinetics were similar for poor and extensive metabolizers. Genetic polymorphism in the expression of CYP2D6 is not expected to affect the pharmacodynamics of galantamine.

Structural basis for the activation of human procaspase-7.

Caspases form a family of proteinases required for the initiation and execution phases of apoptosis. Distinct proapoptotic stimuli lead to activation of the initiator caspases-8 and -9, which in turn activate the common executioner caspases-3 and -7 by proteolytic cleavage. Whereas crystal structures of several active caspases have been reported, no three-dimensional structure of an uncleaved caspase zymogen is available so far. We have determined the 2.9-A crystal structure of recombinant human C285A procaspase-7 and have elucidated the activation mechanism of caspases. The overall fold of the homodimeric procaspase-7 resembles that of the active tetrameric caspase-7. Each monomer is organized in two structured subdomains connected by partially flexible linkers, which asymmetrically occupy and block the central cavity, a typical feature of active caspases. This blockage is incompatible with a functional substrate binding site/active site. After proteolytic cleavage within the flexible linkers, the newly formed chain termini leave the cavity and fold outward to form stable structures. These conformational changes are associated with the formation of an intact active-site cleft. Therefore, this mechanism represents a formerly unknown type of proteinase zymogen activation.

The 2.0-A crystal structure of tachylectin 5A provides evidence for the common origin of the innate immunity and the blood coagulation systems.

Because invertebrates lack an adaptive immune system, they had to evolve effective intrinsic defense strategies against a variety of microbial pathogens. This ancient form of host defense, the innate immunity, is present in all multicellular organisms including humans. The innate immune system of the Japanese horseshoe crab Tachypleus tridentatus, serving as a model organism, includes a hemolymph coagulation system, which participates both in defense against microbes and in hemostasis. Early work on the evolution of vertebrate fibrinogen suggested a common origin of the arthropod hemolymph coagulation and the vertebrate blood coagulation systems. However, this conjecture could not be verified by comparing the structures of coagulogen, the clotting protein of the horseshoe crab, and of mammalian fibrinogen. Here we report the crystal structure of tachylectin 5A (TL5A), a nonself-recognizing lectin from the hemolymph plasma of T. tridentatus. TL5A shares not only a common fold but also related functional sites with the gamma fragment of mammalian fibrinogen. Our observations provide the first structural evidence of a common ancestor for the innate immunity and the blood coagulation systems.

Crystal structure of a novel mid-gut procarboxypeptidase from the cotton pest Helicoverpa armigera.

The cotton bollworm Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) is one of the most serious insect pests in Australia, India and China. The larva causes substantial economical losses to legume, fibre, cereal oilseed and vegetable crops. This pest has proven to be difficult to control by conventional means, mainly due to the development of pesticide resistance. We present here the 2.5 A crystal structure from the novel procarboxypeptidase (PCPAHa) found in the gut extracts from H. armigera larvae, the first one reported for an insect. This metalloprotease is synthesized as a zymogen of 46.6 kDa which, upon in vitro activation with Lys-C endoproteinase, yields a pro-segment of 91 residues and an active carboxypeptidase moiety of 318 residues. Both regions show a three-dimensional structure quite similar to the corresponding structures in mammalian digestive carboxypeptidases, the most relevant structural differences being located in the loops between conserved secondary structure elements, including the primary activation site. This activation site contains the motif (Ala)(5)Lys at the C terminus of the helix connecting the pro- and the carboxypeptidase domains. A remarkable feature of PCPAHa is the occurrence of the same (Ala)(6)Lys near the C terminus of the active enzyme. The presence of Ser255 in PCPAHa instead of Ile and Asp found in the pancreatic A and B forms, respectively, enlarges the S1' specificity pocket and influences the substrate preferences of the enzyme. The C-terminal tail of the leech carboxypeptidase inhibitor has been modelled into the PCPAHa active site to explore the substrate preferences and the enzymatic mechanism of this enzyme.

The structure of calcium-free human m-calpain: implications for calcium activation and function.

The calpains form a growing family of structurally related intracellular multidomain cysteine proteinases containing a papain-related catalytic domain, whose activity depends on calcium. The calpains are believed to play important roles in cytoskeletal remodeling processes, cell differentiation, apoptosis and signal transduction, but are also implicated in muscular dystrophy, cardiac and cerebral ischemia, platelet aggregation, restenosis, neurodegenerative diseases, rheumatoid arthritis and cataract formation. The best characterized calpains, the ubiquitously expressed mu- and m-calpains, are heterodimers consisting of a common 30-kDa small and a variable 80-kDa subunit. The recently determined crystal structures of human and rat m-calpain crystallized in the absence of calcium essentially explain the inactivity of the apoform by catalytic domain disruption, indicate several sites where calcium could bind causing reformation of a papain-like catalytic domain, and additionally reveal modes by which phospholipid membranes could reduce the calcium requirement. Current evidence points to a cooperative interaction of several sites, which, upon calcium binding, trigger the reformation of a papain-similar catalytic domain.

Substrate specificity determinants of human macrophage elastase (MMP-12) based on the 1.1 A crystal structure.

The macrophage elastase enzyme (MMP-12) expressed mainly in alveolar macrophages has been identified in the mouse lung as the main destructive agent associated with cigarette smoking, which gives rise to emphysema, both directly via elastin degradation and indirectly by disturbing the proteinase/antiproteinase balance via inactivation of the alpha1-proteinase inhibitor (alpha1-PI), the antagonist of the leukocyte elastase. The catalytic domain of human recombinant MMP-12 has been crystallized in complex with the broad-specificity inhibitor batimastat (BB-94). The crystal structure analysis of this complex, determined using X-ray data to 1.1 A and refined to an R-value of 0.165, reveals an overall fold similar to that of other MMPs. However, the S-shaped double loop connecting strands III and IV is fixed closer to the beta-sheet and projects its His172 side-chain further into the rather hydrophobic active-site cleft, defining the S3 and the S1-pockets and separating them from each other to a larger extent than is observed in other MMPs. The S2-site is planar, while the characteristic S1'-subsite is a continuous tube rather than a pocket, in which the MMP-12-specific Thr215 replaces a Val residue otherwise highly conserved in almost all other MMPs. This alteration might allow MMP-12 to accept P1' Arg residues, making it unique among MMPs. The active-site cleft of MMP-12 is well equipped to bind and efficiently cleave the AlaMetPhe-LeuGluAla sequence in the reactive-site loop of alpha1-PI, as occurs experimentally. Similarities in contouring and particularly a common surface hydrophobicity both inside and distant from the active-site cleft explain why MMP-12 shares many substrates with matrilysin (MMP-7). The MMP-12 structure is an excellent template for the structure-based design of specific inhibitors for emphysema therapy and for the construction of mutants to clarify the role of this MMP.

Structural basis for possible calcium-induced activation mechanisms of calpains.

The calpains form a growing family of structurally related intracellular multidomainal cysteine proteinases, which exhibit a catalytic domain distantly related to papain. In contrast to papain, however, their activity in most cases depends on calcium. The calpains are believed to play important roles in cytoskeletal remodeling processes, cell differentiation, apoptosis and signal transduction, but have also been implicated in muscular dystrophy, ischemia, traumatic brain injury, neurodegenerative diseases, rheumatoid arthritis and cataract formation. The best characterized calpains are the ubiquitously expressed mu- and m-calpains, consisting of a common 30 kDa small S-subunit (domains V and VI) and slightly differing 80 kDa large L-subunits (domains I to IV). We have recently determined the 2.3 A structure of recombinant full-length human m-calpain in the absence of calcium, which reveals that the catalytic domain and the two calmodulin-like domains, previously believed to represent the unique calcium switch, are not positioned adjacent to each other, but are separated by the beta-sandwich domain III, which distantly resembles C2 domains. Although the catalytic domain of apocalpain is strongly disrupted compared to papain (which explains its inactivity in the absence of calcium), the crystal structure reveals several sites where calcium could bind, thereby causing a subdomain fusion to form a papain-like catalytic center. All current evidence points to the cooperative interaction of several calcium binding sites. Sites identified include the three EF-hand binding sites in each calmodulin-like domain, the negatively charged segments arranged around the active-site cleft (provided by both catalytic subdomains), as well as an exposed acidic loop of domain III, whose charge compensation could allow the adjacent barrel-like subdomain IIb to move toward the helical subdomain IIa. The Gly-rich S-chain N-terminus and the calcium-loaded acidic loop could target the conventional calpains to cellular/nuclear membranes, thereby explaining their strongly reduced calcium requirement in vivo and in vitro in the presence of acidic phospholipids.

Fine mapping of inhibitory anti-factor V antibodies using factor V C2 domain mutants. Identification of two antigenic epitopes involved in phospholipid binding.

Hemorrhagic factor V inhibitors frequently bind to the second C-type (C2) domain of factor V and interfere with phospholipid binding. To define specific residues recognized by inhibitors from four patients (one bovine thrombin-induced and three spontaneous antibodies), epitope mapping was performed using recombinant human factor V lacking most of the B-type domain (FV des B) and alanine-substituted mutants within the C2 domain (FV des B C2 mutants). FV des B C2 mutants located in the region between Lys2060 and Glu2069 were resistant to inhibition by three IgG preparations including the bovine thrombin-induced antibody in both prothrombinase and phospholipid-binding assays. In contrast, mutations at Lys2087 and Lys2092/Glu2096 were significantly resistant to inhibition by the fourth IgG preparation in both prothrombinase and phospholipid-binding assays. These results confirm interference of phospholipid binding by hemorrhagic factor V inhibitors and support the role(s) of these residues in phospholipid binding.

Cloning, purification, crystallization and preliminary X-ray diffraction analysis of the antistasin-type inhibitor ghilanten (domain I) from Haementeria ghilianii in complex with porcine beta-trypsin.

Ghilanten, isolated from the leech Haementeria ghilianii, is a potent two-domain anticoagulant protein homologous to the factor Xa inhibitor antistasin. A synthetic gene encoding the amino-terminal domain of ghilanten (ghilanten-D1) was constructed, expressed in the methylotrophic yeast Pichia pastoris and purified by heparin-Sepharose chromatography. Recombinant ghilanten-D1 inhibits bovine trypsin and human factor Xa with equilibrium inhibition constants (K(i)) of 126 and 1.2 nM, respectively. Ghilanten-D1 has been crystallized in complex with porcine beta-trypsin; three different-looking but isomorphous crystal forms were obtained, each belonging to the orthorhombic space group P2(1)2(1)2(1). These crystals diffracted to beyond 3.6 A resolution using a rotating-anode X-ray source. A data set complete to 3.7 A resolution was collected.

Bivalent inhibition of human beta-tryptase.

BACKGROUND: Human beta-tryptase is a mast cell specific trypsin-like serine protease that is thought to play a key role in the pathogenesis of diverse allergic and inflammatory disorders like asthma and psoriasis. The recently resolved crystal structure revealed that the enzymatically active tetramer consists of four quasi-identical monomers. The spatial display of the four identical active sites represents an ideal basis for the rational design of bivalent inhibitors. RESULTS: Based on modeling experiments homobivalent inhibitors were constructed using (i) 6A,6D-dideoxy-6A,6D-diamino-beta-cyclodextrin as a rigid template to bridge the space between the two pairs of identical active sites and (ii) 3-(aminomethyl)benzene as a headgroup to occupy the arginine/lysine specific S1 subsites. A comparative analysis of the inhibitory potencies of synthetic constructs that differ in size and type of the spacer between headgroup and template revealed that the construct contained two 3-(aminomethyl)benzenesulfonyl-glycine groups linked to the 6A,6D-diamino groups of beta-cyclodextrin as an almost ideal bivalent inhibitor with a cooperativity factor of 1.9 vs. the ideal value of 2. The bivalent binding mode is supported by the inhibitor/tetramer ratio of 2:1 required for inactivation of tryptase and by X-ray analysis of the inhibitor/tryptase complex. CONCLUSION: The results obtained with the rigid cyclodextrin template underlined the importance of a minimal loss of conformational entropy in bivalent binding, but also showed the limitations imposed by such rigid core molecules in terms of optimal occupancy of binding sites and thus of enthalpic strains in bidentate binding modes. The main advantage of bivalent inhibitors is their high selectivity for the target enzyme that can be achieved utilizing the principle of multivalency.