Future aspects of plant derived bioactive metabolites as therapeutics to combat benign prostatic hyperplasia

ETHNOPHARMACOLOGICAL RELEVANCE

Benign prostatic hyperplasia (BPH), characterized by prostate enlargement due to cell proliferation, is a common urinary disorder in men over 50, manifesting as lower urinary tract symptoms (LUTS). Currently, several therapeutic options are accessible for treating BPH, including medication therapy, surgery and watchful waiting. Conventional drugs such as finasteride and dutasteride are used as 5α-reductase inhibitors for the treatment of BPH. However long-term use of these drugs is restricted due to their unpleasant side effects. Despite the range of available medical therapies, the effective treatment against BPH is still inadequate. Certain therapeutic plants and their phytochemicals have the aforementioned goals and work by regulating this enzyme.

AIM OF THE STUDY

This review aims to provide a comprehensive insight to advancements in diagnosis of BPH, modern treatment methods and the significance of ethnobotanically relevant medicinal plants as alternative therapeutics for managing BPH.

MATERIAL AND METHODS

A thorough and systematic literature search was performed using electronic databases and search engines such as PubMed, Web of Science, NCBI and SciFinder till October 2023. Specific keywords such as "benign prostatic hyperplasia", "medicinal plants", "phytochemicals", "pharmacology", "synergy", "ethnobotany", "5-alpha reductase", "alpha blocker" and "toxicology". By include these keywords, a thorough investigation of pertinent papers was assured, and important data about the many facets of BPH could be retrieved.

RESULTS

After conducting the above investigation, 104 herbal remedies were found to inhibit Phosphodiesterase-5 (PDE-5) inhibition, alpha-blockers, or 5α -reductase inhibition effects which are supported by in vitro, in vivo and clinical trial studies evidence. Of these, 89 plants have ethnobotanical significance as alpha-blockers, alpha-reductase inhibition, or PDE-5 inhibition, and the other fifteen plants were chosen based on their ability to reduce BPH risk factors. Several phytocompounds, including, rutaecarpine, vaccarin, rutin, kaempferol, β-sitosterol, quercetin, dicaffeoylquinic acid, rutaevin, and phytosterol-F have been reported to be useful for the management of BPH. The use of combination therapy offers a strong approach to treating long-term conditions compare to single plant extract drugs. Furthermore, several botanical combinations such as lycopene and curcumin, pumpkin seed oil and saw palmetto oil, combinations of extracts from Funtumia africana (Benth.) Stapf and Abutilon mauritianum (Jacq.) Medik., and Hypselodelphys poggeana (K.Schum.) Milne-Redh. and Spermacoce radiata (DC.) Sieber ex Hiern are also supported through in vitro and in vivo studies for managing BPH through recuperation in patients with chronic long-term illnesses, as measured by the International Prostate Symptom Score.

CONCLUSION

The review proposes and endorses careful utilization of conventional medications that may be investigated further to discover possible PDE-5, 5 alpha-reductase, an alpha-blocker inhibitor for managing BPH. Even though most conventional formulations, such as 5 alpha-reductase, are readily available, systemic assessment of the effectiveness and mechanism of action of the herbal constituents is still necessary to identify novel chemical moieties that can be further developed for maximum efficacy. However, there exist abundant botanicals and medicinal plants across several regions of Africa, Asia, and the Americas, which can be further studied and developed for utilization as a potential phytotherapeutic for the management of BPH.

Comprehensive Analysis of Bioactive Compounds in Wild Ganoderma applanatum Mushroom from Kerala, South India: Insights into Dietary Nutritional, Mineral, Antimicrobial, and Antioxidant Activities

The present study focused on the mushroom Ganoderma, which has been used in Eastern countries for centuries as a food and medicinal source. Specifically, the fruiting bodies of Ganoderma applanatum from the Kerala Forest Research Institute in Thirussur, Kerala, India, were analyzed for their nutritional and medicinal properties. The methanolic extracts of G. applanatum were used to examine secondary metabolites and proximate profiles, revealing the presence of various phytochemicals such as terpenoids, phenolics, glycosides, alkaloids, flavonoids, and saponins. Further analysis revealed the presence of significant amounts of calcium, sodium, phosphorus, and manganese. The compounds were characterized using chromatographic analysis, FTIR, and GC-MS, which revealed potential therapeutic compounds with C-H and C-O bonds in the amide group, β-glycosides, and C-C/C-O vibrations of phenolic substances. Mushroom extract at a concentration of 100 µg mL-1 exhibited potent antimicrobial activity against various pathogens. This study suggests that G. applanatum has a rich biochemical composition and pharmacological potential, making it a promising candidate for drug development and traditional medicine, and contributes valuable insights into its diverse therapeutic applications.

Enhanced bactericidal, antibiofilm and antioxidative response of Lawsonia inermis leaf extract synthesized ZnO NPs loaded with commercial antibiotic

Globally, antibiotic resistance is a challenging issue in healthcare sector. The emergence of multiple drug-resistant bacteria has forced us to modify existing medicines and or formulate newer medicines that are effective and inexpensive. In this perspective, this study involves the formation of zinc oxide nanoparticles (ZnO NPs) by utilizing the Lawsonia inermis (Li) leaf extract. The prepared L. inermis leaf extract mediated ZnO NPs (Li-ZnO NPs) were bio-physically characterized. The antibacterial and radical scavenging effects of Li-ZnO NPs were evaluated. In addition, ZnO NPs were conjugated with standard antibiotic (ciprofloxacin) and its drug loading efficiency, drug release and antibacterial efficacy were tested and compared with non-drug loaded ZnO NPs. An absorbance peak at 340 nm was noted for Li-ZnO NPs. After conjugation with the drug, two absorbance peaks- one at 242 nm characteristic of ciprofloxacin and the other at 350 nm characteristics of ZnO NPs were observed. The crystallite size was 18.7 nm as determined by XRD. The antibacterial effect was higher on Gram-positive (S. aureus and S. pyogenes) than the Gram-negative pathogens (E. coli and K. pneumoniae). Inhibition of S. aureus and S. pyogenes biofilm at 100 μg mL-1were, respectively, 97.5 and 92.6%. H2O2 free radicals was inhibited to 90% compared to the standard ascorbic acid at 100 μg mL-1. After drug loading, the FTIR spectrum confirmed the existence of ciprofloxacin peaks at 965 cm-1 and Zn-O bond at 492 cm-1. The drug loading capacity of 15 nm sized ZnO NPs was higher (58, 75, 90 and 95% at 1, 2.5, 5 and 10% drug concentrations, respectively) compared to 20 nm. Similarly, the percentage of drug (ciprofloxacin) released from 15 nm ZnO NPs were increased to 90% at 10% drug-loaded samples, respectively. Also, the antibiotic loaded ZnO NPs had significant antibacterial effects against tested bacteria compared to Li-ZnO NPs and ciprofloxacin alone. This revealed that the antibiotic loaded ZnO NPs offer a sustainable route to treat multi-drug-resistant bacterial infections.

Molecular detection of Orientia tsutsugamushi in ectoparasites & their small mammal hosts captured from scrub typhus endemic areas in Madurai district, India

BACKGROUND OBJECTIVES

Scrub typhus, caused by Orientia tsutsugamushi present in small mammals harbouring the ectoparasites. A study was undertaken to detect the pathogen present in small mammals and its ectoparasites in the scrub typhus-reported areas.

METHODS

The small mammals (rodents/shrews) and its ectoparasites were screened for O. tsutsugamushi using nested PCR amplification of the groEL gene. Small mammals were collected by trapping and screened for ectoparasites (mites, ticks and fleas) by combing method.

RESULTS

All the chigger mites collected were tested negative for O. tsutsugamushi . Interestingly, adult non-trombiculid mites ( Oribatida sp., Dermanyssus gallinae ), fleas ( Xenopsylla astia, X. cheopis, Ctenophalides felis and Ctenophalides sp.) and ticks ( Rhipicephalus sanguineus , R. haemaphysaloides ) screened were found to be positive for O. tsutsugamushi , which the authors believe is the first report on these species globally. Bandicota bengalensis with O. tsutsugamushi infection is reported for the first time in India. The O. tsutsugamushi groEL sequences from the positive samples were similar to the reference strains, Karp and Ikeda and phylogenetically clustered in clade IV with less evolutionary divergence. The blood samples of Rattus rattus , Suncus murinus and B. bengalensis collected from this area were tested positive for O. tsutsugamushi ; interestingly, the sequence similarity was much pronounced with their ectoparasites indicating the transmission of the pathogen to host or vice versa .

INTERPRETATION CONCLUSIONS

The outcome of the present investigations widened our scope on the pathogens present in ectoparasites and rodents/shrews from this area. This will help to formulate the required vector control methods to combat zoonotic diseases.

Exopolysaccharide from Lactococcus hircilactis CH4 and Lactobacillus delbrueckii GRIPUMSK as new therapeutics to treat biofilm pathogens, oxidative stress and human colon adenocarcinoma

Naturally occurring biopolymers like exopolysaccharides (EPS) secreted by lactic acid bacteria (LAB) has gained significant attention as they are cost effective, renewable and safe. In order to prevent the rapid increase in antibiotic resistant bacteria, the EPS of LAB offers novel approach of targeting the antibiotic resistant pathogens by limiting their effects on environment. Accordingly, in this study, the production, purification, characterization and biological properties of exopolysaccharides from Lactococcus hircilactis strain CH4 and Lactobacillus delbrueckii strain GRIPUMSK were performed. The optimization of lactic acid bacterial strains for exopolysaccharide production was done by response surface methodology and changing the carbon sources in the growth media. The carbohydrate and protein of exopolysaccharide 1 were 79.7 % and 8.7 % respectively and exopolysaccharide 2 were 75.2 % and 9.3 % respectively. When compared with the commercial emulsifier sodium dodecyl sulfate, both the exopolysaccharides have shown good emulsifying activity. Both the exopolysaccharides were linear homo-polysaccharide as determined by Fourier transform infrared spectroscopy and Nuclear magnetic resonance spectra. Scanning electron microscopy showed that the exopolysaccharides were porous and capable of holding water. The exopolysaccharides were partially crystalline as confirmed by X-ray diffraction spectra. Exopolysaccharides from L. hircilactis and L. delbrueckii exhibited significant antimicrobial activity against H. pylori, S. flexneri, S. pyogenes, E. faecalis and C. albicans. Both the exopolysaccharides revealed significant 2,2-diphenyl-1-picrylhydrazyl and hydrogen peroxide scavenging ability with the IC50 value of 100 μg/ml and 80 μg/ml respectively. Exopolysaccharides from L. hircilactis and L. delbrueckii at 100 μg/ml showed significant anticancer activity on HT-29 cells with 58.4 % and 58.7 % respectively. These findings proved that exopolysaccharides from the two selected lactic acid bacterial strains could be explored as natural bioactive carbohydrate polymer for biomedical applications.

Outcomes of peroral endoscopic myotomy in patients with achalasia and prior bariatric surgery: A multicenter experience

Peroral endoscopic myotomy (POEM) in patients with achalasia who are status post bariatric surgery may be technically challenging due to postsurgical scarring and altered anatomy. The aim of the study was to assess the efficacy and safety of POEM for achalasia in patients with prior bariatric surgery. A review of prospectively maintained databases at three tertiary referral centers from January 2015 to January 2021 was performed. The primary outcome of interest was clinical success, defined as a post-treatment Eckardt score ≤ 3 or improvement in Eckardt score by ≥ 1 when the baseline score was <3, and improvement of symptoms. Secondary outcomes were adverse event rates and symptom recurrence. Sixteen patients status post Roux-en-Y gastric bypass (n = 14) and sleeve gastrectomy (n = 2) met inclusion criteria. Indications for POEM were achalasia type I (n = 2), type II (n = 9), and type III (n = 5). POEM was performed either by anterior or posterior approach. The pre-POEM mean integrated relaxation pressure was 26.2 ± 7.6 mm Hg. The mean total myotomy length was 10.2 ± 2.7 cm. The mean length of hospitalization was 1.4 ± 0.7 days. Pre- and postprocedure Eckardt scores were 6.1 ± 2.1 and 1.7 ± 1.8, respectively. The overall clinical success rate was 93.8% (15/16) with mean follow-up duration of 15.5 months. One patient had esophageal leak on postprocedure esophagram and managed endoscopically. Dysphagia recurred in two patients, which was successfully managed with pneumatic dilation with or without botulinum toxin injection. POEM appears to be safe and effective in the management of patients with achalasia who have undergone prior bariatric surgery.

Liquid Nitrogen Spray Cryotherapy in Treatment of Barrett's Esophagus, where do we stand? A Systematic Review and Meta-Analysis

Radiofrequency ablation (RFA) is the preferred treatment option for Barrett's esophagus (BE) to achieve complete eradication (CE) of dysplasia (D), and intestinal metaplasia (IM). Cryotherapy, using liquid nitrogen (LNC), is a cold-induced tissue-injury technique option for the ablation of BE. We conducted a systematic review and meta-analysis to assess the overall efficacy and safety of LNC in the treatment of BE. We conducted a search of multiple electronic databases and conference proceedings from inception through June 2018. The primary outcome was to estimate the pooled rates of CE-IM, CE-D, and CE-HGD. The secondary outcome was to estimate the risk of adverse events and recurrence of disease after LNC. Nine studies reported 386 patients who were treated with LNC. The pooled rate of CE-IM was 56.5% (95% CI 48.5-64.2, I2 = 47), pooled rate of CE-D was 83.5% (95% CI 78.3-87.7, I2 = 22.8), and pooled rate of CE-HGD was 86.5% (95% CI 64.4-95.8, I2 = 88.1). Rate of adverse events was 4.7%, and the risk of BE recurrence was 12.7%. On subgroup analysis, the pooled rate of CE-IM with LNC in patients who failed RFA was 58.4% (95% CI 47.2-68.8, I2 = 32.5), and the pooled rate of CE-D in the same population was 81.9% (95% CI 72.5-88.6, I2 = 5.9). CE-D rates with LNC are comparable to RFA while CE-IM rates appear to be lower than the rates achievable with RFA. CE-IM rate in RFA failed patients is 58.4% and thus LNC is a rescue option to consider in this population.

Systematic review with meta-analysis: prevalent vs. incident oesophageal adenocarcinoma and high-grade dysplasia in Barrett's oesophagus

BACKGROUND

The proportion of oesophageal adenocarcinoma that is detected concurrently with initial Barrett's oesophagus diagnosis is not well studied.

AIM

To compare the proportion of prevalent adenocarcinoma vs. incident adenocarcinoma found during surveillance of Barrett's.

METHODS

We performed a systematic search of MEDLINE, EMBASE and Web of Science (from their inception to 31 May 2015) for cohort studies in adults with Barrett's (nondysplastic Barrett's ± Barrett's with low-grade dysplasia) with minimum average follow-up of 3 years, and providing numbers of prevalent adenocarcinoma detected (concurrently with Barrett's diagnosis and up to 1 year afterwards) vs. incident adenocarcinoma detected (greater than 1 year after Barrett's diagnosis). Pooled weighted proportions of prevalent and incident adenocarcinoma were calculated, using a random effects model.

RESULTS

On meta-analysis of 13 studies reporting on 603 adenocarcinomas in 9657 Barrett's patients, 85.1% of adenocarcinomas were classified as prevalent [95% confidence interval (CI), 78.1-90.2%) and 14.9% as incident (95% CI, 9.8-21.9%), with substantial heterogeneity (I(2) = 66%). Among nine studies reporting on 787 high-grade dysplasia and oesophageal adenocarcinomas in 8098 Barrett's patients, the proportion of prevalent high-grade dysplasia-oesophageal adenocarcinoma was similar at 80.5% (95% CI, 68.1-88.8%, I(2) = 87%). These results remained stable across multiple subgroup analyses including study quality, setting, duration of follow-up and presence of baseline dysplasia.

CONCLUSIONS

In our meta-analysis, four of five patients diagnosed with adenocarcinoma or high-grade dysplasia at index endoscopy or within 1 year of Barrett's follow-up were considered to be prevalent cases. Continued efforts are needed to identify patients with Barrett's before the development of adenocarcinoma.

Trade off between variable and fixed size normalization in orthogonal polynomials based iris recognition system

Iris normalization is an important stage in any iris biometric, as it has a propensity to trim down the consequences of iris distortion. To indemnify the variation in size of the iris owing to the action of stretching or enlarging the pupil in iris acquisition process and camera to eyeball distance, two normalization schemes has been proposed in this work. In the first method, the iris region of interest is normalized by converting the iris into the variable size rectangular model in order to avoid the under samples near the limbus border. In the second method, the iris region of interest is normalized by converting the iris region into a fixed size rectangular model in order to avoid the dimensional discrepancies between the eye images. The performance of the proposed normalization methods is evaluated with orthogonal polynomials based iris recognition in terms of FAR, FRR, GAR, CRR and EER.

Liver transplantation of hepatitis B surface antigen positive donors to hepatitis B core antibody recipients: analysis of 27 patients

AIM

Shortage of donor livers is the major limiting factor for liver transplantation (LT). While livers from patients with past infection of Hepatitis-B (HBcAb+) are commonly used as donors, scant data exists on outcomes following transplantation of HBsAg+ donor livers. The impact of donor HBsAg positivity on recipient survival is currently analyzed.

METHODS

Post hoc analysis of all adults undergoing LT from October 1987-September 2010 registered in United Network for Organ Sharing/Organ Procurement and Transplantation Network, a concurrent, limited access database of all American LT recipients. Only recipients who were HBcAb+ were analyzed. LTs with missing donor or recipient serologic parameters for Hepatitis-B were excluded. Significant predictors of survival were determined by univariate analysis. Cox proportional hazards model was used to determine independent risk predictors in the multivariate analysis.

RESULTS

The population consisted of 13,329 LT recipients. The mean age of donors and recipients were 40±16 years and 52±9 years respectively. The mean follow-up was 3.7 years. Study population included 27 recipients transplanted with HBsAg+ grafts, of whom 7 (28%) died. Outcomes were adjusted for donor age, recipient age, donor gender, recipient gender, type of LT, MELD score, HCV status, previous LT, and cold ischemic time. On multivariate analysis, LT recipient outcomes were not significantly different for HBsAg+ donors versus donors without prior hepatitis B infection (HR: 1.14, 95% CI: 0.93-1.39, P=0.17). Kaplan-Meier curves revealed no significant survival difference between the two groups.

CONCLUSION

These results suggest that donor HBsAg positivity did not affect overall survival of LT recipients. These findings could potentially expand the pool of liver donors.

A rare cause of dysphagia in a HIV patient--esophageal pseudodiverticulosis

Esophageal pseudodiverticulosis is a rare clinical entity with a slight male predominance (1). The condition is caused by cystic dilation of the sub mucosal glands and hence is not true diverticulosis. This is usually a benign condition, affecting the distal third of esophagus. It has been associated with reflux esophagitis, strictures and candidiasis. Patients with esophageal pseudodiverticulosis may present with progressive dysphagia, though most cases are asymptomatic. Perforation (2), bleeding (3) and mediastinitis have rarely been described. To the best of our knowledge, the occurrence of this rare disease in HIV patients has been described only once before (4). We report the second case of esophageal pseudodiverticulosis occurring in a HIV patient.

Community-based control of Aedes aegypti by adoption of eco-health methods in Chennai City, India

Background

Dengue is highly endemic in Chennai city, South India, in spite of continuous vector control efforts. This intervention study was aimed at establishing the efficacy as well as the favouring and limiting factors relating to a community-based environmental intervention package to control the dengue vector Aedes aegypti.

Methods

A cluster randomized controlled trial was designed to measure the outcome of a new vector control package and process analysis; different data collection tools were used to determine the performance. Ten randomly selected intervention clusters (neighbourhoods with 100 houses each) were paired with ten control clusters on the basis of ecological/entomological indices and sociological parameters collected during baseline studies. In the intervention clusters, Aedes control was carried out using a community-based environmental management approach like provision of water container covers through community actors, clean-up campaigns, and dissemination of dengue information through schoolchildren. The main outcome measure was reduction in pupal indices (pupae per person index), used as a proxy measure of adult vectors, in the intervention clusters compared to the control clusters.

Results

At baseline, almost half the respondents did not know that dengue is serious but preventable, or that it is transmitted by mosquitoes. The stakeholder analysis showed that dengue vector control is carried out by vertically structured programmes of national, state, and local administrative bodies through fogging and larval control with temephos, without any involvement of community-based organizations, and that vector control efforts were conducted in an isolated and irregular way. The most productive container types for Aedes pupae were cement tanks, drums, and discarded containers. All ten intervention clusters with a total of 1000 houses and 4639 inhabitants received the intervention while the ten control clusters with a total of 1000 houses and 4439 inhabitants received only the routine government services and some of the information education and communication project materials. The follow-up studies showed that there was a substantial increase in dengue understanding in the intervention group with only minor knowledge changes in the control group. Community involvement and the partnership among stakeholders (particularly women’s self-help groups) worked well. After 10 months of intervention, the pupae per person index was significantly reduced to 0.004 pupae per person from 1.075 (P = 0.020) in the intervention clusters compared to control clusters. There were also significant reductions in the Stegomyia indices: the house index was reduced to 4.2%, the container index to 1.05%, and the Breteau index to 4.3 from the baseline values of 19.6, 8.91, and 30.8 in the intervention arm.

Conclusion

A community-based approach together with other stakeholders that promoted interventions to prevent dengue vector breeding led to a substantial reduction in dengue vector density.

Studies on community knowledge and behavior following a dengue epidemic in Chennai city, Tamil Nadu, India

In 2001, a major dengue outbreak was recorded in Chennai city, with 737 cases (90%) out of a total of 861 cases recorded from Tamil Nadu state. A KAP survey was carried out to assess the community knowledge, attitude and practice on dengue fever (DF), following the major dengue outbreak in 2001. A pre- tested, structured questionnaire was used for data collection. The multistage cluster sampling method was employed and 640 households (HHs) were surveyed. Among the total HHs surveyed, 34.5% of HHs were aware of dengue and only 3.3% of HHs knew that virus is the causative agent for DF. Majority of the HHs (86.5%) practiced water storage and only 3% of them stored water more than 5 days. No control measures were followed to avoid mosquito breeding in the water holding containers by majority of HHs (65%). Sixty percent of HHs did not know the biting behaviour of dengue vector mosquitoes. The survey results indicate that the community knowledge was very poor on dengue, its transmission, vector breeding sources, biting behavior and preventive measures. The lack of basic knowledge of the community on dengue epidemiology and vector bionomics would be also a major cause of increasing trend of dengue in this highly populated urban environment. There is an inevitable need to organize health education programmes about dengue disease to increase community knowledge and also to sensitize the community to participate in integrated vector control programme to resolve the dengue problem.

Entomo-epidemiological investigations on chikungunya outbreak in the Lakshadweep islands, Indian Ocean

BACKGROUND & OBJECTIVE

An outbreak of chikungunya fever characterized by prolonged incapacitation in the Lakshadweep islands in Indian Ocean occurred in November 2006. We undertook the entomological and epidemiological investigations on the Chikungunya outbreak in the Lakshadweep islands, Indian Ocean.

METHODS

Epidemic information in the affected places was obtained from the local hospital records. Entomological observations like larval survey and the adult resting/landing collections by the hand collection methods were individually conducted in the two affected islands Andrott and Kalpeni in November and December 2006.

RESULTS

The main breeding sources of the mosquitoes were the rodent-devoured coconuts, coconut shells, areca nut soaking mud and plastic pots, discarded containers, grinding stones, metal containers and plastic containers. Aedes albopictus was pre-dominantly present in the Lakshadweep islands.

INTERPRETATION & CONCLUSION

It is concluded that the routine campaigns need to be organized regularly within the community highlighting the potential breeding grounds of mosquitoes and the possible control methods. Source reduction strategies like destruction of coconut shells and rodent-devoured coconuts by burning or by burying them inside the ground. Ae. albopictus played major role as the vector mosquitoes responsible for the chikungunya transmission.

Disulfide bond effects on protein stability: designed variants of Cucurbita maxima trypsin inhibitor-V

Attempts to increase protein stability by insertion of novel disulfide bonds have not always been successful. According to the two current models, cross-links enhance stability mainly through denatured state effects. We have investigated the effects of removal and addition of disulfide cross-links, protein flexibility in the vicinity of a cross-link, and disulfide loop size on the stability of Cucurbita maxima trypsin inhibitor-V (CMTI-V; 7 kD) by differential scanning calorimetry. CMTI-V offers the advantage of a large, flexible, and solvent-exposed loop not involved in extensive intra-molecular interactions. We have uncovered a negative correlation between retention time in hydrophobic column chromatography, a measure of protein hydrophobicity, and melting temperature (T(m)), an indicator of native state stabilization, for CMTI-V and its variants. In conjunction with the complete set of thermodynamic parameters of denaturation, this has led to the following deductions: (1) In the less stable, disulfide-removed C3S/C48S (Delta Delta G(d)(50 degrees C) = -4 kcal/mole; Delta T(m) = -22 degrees C), the native state is destabilized more than the denatured state; this also applies to the less-stable CMTI-V* (Delta Delta G(d)(50 degrees C) = -3 kcal/mole; Delta T(m) = -11 degrees C), in which the disulfide-containing loop is opened by specific hydrolysis of the Lys(44)-Asp(45) peptide bond; (2) In the less stable, disulfide-inserted E38C/W54C (Delta Delta G(d)(50 degrees C) = -1 kcal/mole; Delta T(m) = +2 degrees C), the denatured state is more stabilized than the native state; and (3) In the more stable, disulfide-engineered V42C/R52C (Delta Delta G(d)(50 degrees C) = +1 kcal/mole; Delta T(m) = +17 degrees C), the native state is more stabilized than the denatured state. These results show that a cross-link stabilizes both native and denatured states, and differential stabilization of the two states causes either loss or gain in protein stability. Removal of hydrogen bonds in the same flexible region of CMTI-V resulted in less destabilization despite larger changes in the enthalpy and entropy of denaturation. The effect of a cross-link on the denatured state of CMTI-V was estimated directly by means of a four-state thermodynamic cycle consisting of native and denatured states of CMTI-V and CMTI-V*. Overall, the results show that an enthalpy-entropy compensation accompanies disulfide bond effects and protein stabilization is profoundly modulated by altered hydrophobicity of both native and denatured states, altered flexibility near the cross-link, and residual structure in the denatured state.

Distinct Ca2+ binding properties of novel C2 domains of plant phospholipase dalpha and beta

Of the isoforms of plant phospholipase D (PLD) that have been cloned and characterized, PLDalpha requires millimolar levels of Ca(2+) for optimal activity, whereas PLDbeta is most active at micromolar concentrations of Ca(2+). Multiple amino acid sequence alignments suggest that PLDalpha and PLDbeta both contain a Ca(2+)-dependent phospholipid-binding C2 domain near their N termini. In the present study, we expressed and characterized the putative C2 domains of PLDalpha and PLDbeta, designated PLDalpha C2 and PLDbeta C2, by CD spectroscopy, isothermal titration calorimetry, and phospholipid binding assay. Both PLD C2 domains displayed CD spectra consistent with anticipated major beta-sheet structures but underwent spectral changes upon binding Ca(2+); the magnitude was larger for PLDbeta C2. These conformational changes, not shown by any of the previously characterized C2 domains of animal origin, occurred at micromolar Ca(2+) concentrations for PLDbeta C2 but at millimolar levels of the cation for PLDalpha C2. PLDbeta C2 exhibited three Ca(2+)-binding sites: one with a dissociation constant (K(d)) of 0.8 microm and the other two with a K(d) of 24 micrometer. In contrast, isothermal titration calorimetry data of PLDalpha C2 were consistent with 1-3 low affinity Ca(2+)-binding sites with K(d) in the range of 590-470 micrometer. The thermodynamics of Ca(2+) binding markedly differed for the two C2 domains. Likewise, PLDbeta C2 bound phosphatidylcholine (PC), the substrate of PLD, in the presence of submillimolar Ca(2+) concentrations, whereas PLDalpha C2 did so only in the presence of millimolar levels of the metal ion. Both C2 domains bound phosphatidylinoistol 4,5-bisphosphate, a regulator of PC hydrolysis by PLD. However, added Ca(2+) displaced the bound phosphatidylinoistol 4,5-bisphosphate. Ca(2+) and PC binding properties of PLDalpha C2 and PLDbeta C2 follow a trend similar to the Ca(2+) requirements of the whole enzymes, PLDalpha and PLDbeta, for PC hydrolysis. Taken together, the results suggest that the C2 domains of PLDalpha and PLDbeta have novel structural features and serve as handles by which Ca(2+) differentially regulates the activities of the isoforms.

NMR studies of internal dynamics of serine proteinase protein inhibitors: Binding region mobilities of intact and reactive-site hydrolyzed Cucurbita maxima trypsin inhibitor (CMTI)-III of the squash family and comparison with those of counterparts of CMTI-V of the potato I family

Serine proteinase protein inhibitors follow the standard mechanism of inhibition (Laskowski M Jr, Kato I, 1980, Annu Rev Biochem 49:593-626), whereby an enzyme-catalyzed equilibrium between intact (I) and reactive-site hydrolyzed inhibitor (I*) is reached. The hydrolysis constant, Khyd, is defined as [I*]/[I]. Here, we explore the role of internal dynamics in the resynthesis of the scissile bond by comparing the internal mobility data of intact and cleaved inhibitors belonging to two different families. The inhibitors studied are recombinant Cucurbita maxima trypsin inhibitor III (rCMTI-III; Mr 3 kDa) of the squash family and rCMTI-V (Mr approximately 7 kDa) of the potato I family. These two inhibitors have different binding loop-scaffold interactions and different Khyd values--2.4 (CMTI-III) and 9 (CMTI-V)--at 25 degrees C. The reactive-site peptide bond (P1-P1') is that between Arg5 and Ile6 in CMTI-III, and that between Lys44 and Asp45 in CMTI-V. The order parameters (S2) of backbone NHs of uniformly 15N-labeled rCMTI-III and rCMTI-III* were determined from measurements of 15N spin-lattice and spin-spin relaxation rates, and [1H]-15N steady-state heteronuclear Overhauser effects, using the model-free formalism, and compared with the data reported previously for rCMTI-V and rCMTI-V*. The backbones of rCMTI-III [(S2) = 0.71] and rCMTI-III* [(S2) = 0.63] are more flexible than those of rCMTI-V [(S2) = 0.83] and rCMTI-V* [(S2) = 0.85]. The binding loop residues, P4-P1, in the two proteins show the following average order parameters: 0.57 (rCMTI-III) and 0.44 (rCMTI-III*); 0.70 (rCMTI-V) and 0.40 (rCMTI-V*). The P1'-P4' residues, on the other hand, are associated with (S2) values of 0.56 (rCMTI-III) and 0.47 (rCMTI-III*); and 0.73 (rCMTI-V) and 0.83 (rCMTI-V*). The newly formed C-terminal (Pn residues) gains a smaller magnitude of flexibility in rCMTI-III* due to the Cys3-Cys20 crosslink. In contrast, the newly formed N-terminal (Pn' residues) becomes more flexible only in rCMTI-III*, most likely due to lack of an interaction between the P1' residue and the scaffold in rCMTI-III. Thus, diminished flexibility gain of the Pn residues and, surprisingly, increased flexibility of the Pn' residues seem to facilitate the resynthesis of the P1-P1' bond, leading to a lower Khyd value.

Internal mobility of reactive-site-hydrolyzed recombinant Cucurbita maxima trypsin inhibitor-V characterized by NMR spectroscopy: evidence for differential stabilization of newly formed C- and N-termini

The solution structure and internal dynamics of the reactive-site (Lys44-Asp45 peptide bond) hydrolyzed form of recombinant Cucurbita maxima trypsin inhibitor-V (rCMTI-V*) were characterized by the application of two-dimensional 1H-15N NMR methods to the uniformly 15N-labeled protein. The 1H-15N chemical shift correlation spectra of rCMTI-V* were assigned, and the chemical shift data were compared with those available for rCMTI-V [Liu, J., Prakash, O., Cai, M., Gong, Y., Huang, Y., Wen, L., Wen, J. J., Huang, J.-K., & Krishnamoorthi, R. (1996) Biochemistry 35, 1516-1524] and CMTI-V* [Cai, M., Gong, Y., Prakash, O., & Krishnamoorthi, R. (1995) Biochemistry 34, 12087-12094] for which three-dimensional solution structures have been determined. It was deduced that the solution structure of rCMTI-V* was almost the same as that of CMTI-V*. 15N spin-lattice and spin-spin relaxation rate constants (R1 and R2, respectively) and ¿1H¿-15N steady-state heteronuclear Overhauser effects were measured for the peptide NH units and arginine and tryptophan N epsilon H groups in rCMTI-V*, and the model-free parameters [Lipari, G., & Szabo, A. (1982) J. Am. Chem. Soc. 104, 4546-4559, 4559-4570] were computed. Most of the backbone of rCMTI-V* is found to be highly constrained (S2 = 0.85), including the N-terminal residues 3-6 (S2 = 0.77). Residues 39-44, forming the C-terminal fragment of the binding loop, exhibit increased mobility (S2 = 0.51); however, the N-terminal segment (residues 46-48) retains rigidity as in the intact form (S2 = 0.83). The S2 values, 0.78 and 0.59, respectively, of Arg50 and Arg52 side chain NHs provide evidence not only for the conservation of the Arg hydrogen-bonds with the binding loop segments but also for the difference in strength between them. This is consistent with the earlier observation made from a study of rCMTI-V at two different pHs and its R50 and R52 mutants [Cai, M., Huang, Y., Prakash, O., Wen, L., Dunkelbarger, S. P., Huang, J.-K., Liu, J., & Krishnamoorthi, R. (1996) Biochemistry 35, 4784-4794]. The dynamical results suggest the mainchain oxygen atom of Asp45 as the hydrogen bond acceptor of Arg50. Residues Trp9 and Trp54, which interact with many others in the protein scaffold and the binding loop region, respectively, remain rigid in the cleaved inhibitor with the S2 values of 0.84 and 0.71 determined for their respective N epsilon Hs. The internal dynamics of rCMTI-V* was compared with that of the noncovalent complex formed between the two fragments of reactive-site-hydrolyzed chymotrypsin inhibitor-2 from barley seeds [CI-2; Shaw, G. L., Davis, B., Keeler, J., & Fersht, A. R. (1995) Biochemistry 34, 2225-2233], another potato I family inhibitor that lacks the Cys3-Cys48 disulfide present in rCMTI-V*.

Differential modulation of binding loop flexibility and stability by Arg50 and Arg52 in Cucurbita maxima trypsin inhibitor-V deduced by trypsin-catalyzed hydrolysis and NMR spectroscopy

The side chains of Arg50 and Arg52 iin Cucurbita maxima trypsin inhibitor-V (CMTI-V) anchor the binding loop to the scaffold region [Cai, M., Gong, Y., Kao, J.L-F., & Krishnamoorthi, R. (1995) Biochemistry 34, 5201-5211]. The consequences of these hydrogen-bonding and electrostatic interactions on the conformational flexibility and stability of the binding loop were evaluated by trypsin-catalyzed hydrolysis of CMTI-V mutants, in which each of the arginines was individually replaced with Ala, Lys, or Gln by genetic engineering methods. All mutants exhibited significantly increased vulnerability to the protease attack at many sites, including the reactive-site (Lys44-Asp45 peptide bond), with the R50 mutants showing much more pronounced effects than the R52 counterparts. For CmTI-V and the mutants studied, a qualitative correlation was inferred between binding loop flexibility and retention time on a reverse-phase high-pressure liquid chromatography C-18 column. The R50 mutants were found to be more flexible than the corresponding R52 versions. These results demonstrate that Arg50 contributes more to the stability and function of CMTI-V. The differing strengths of the hydrogen bonds made by Arg50 and Arg52 were characterized by determining the internal dynamics of their side chains at pH 5.0 and 2.5: 15N NMR longitudinal and transverse relaxation rates and 15N-1H nuclear Overhauser effect (NOE) enhancements were measured for the main-chain and side-chain NH groups in 15N-labeled recombinant CMTI-V (rCMTI-V) and the model-free parameters [Lipari, G., & Szabo, A.(1982) J. Am. Chem. Soc. 104, 4546-59; 4559-4570] were calculated. At both pH 5.0 and 2.5, the arginines at positions 26, 47, 58 and 66 are found to be highly mobile, as the caluculated general order parameters, S2 values, of their NepsilonH groups fall in the range 0.03-0.18. The corresponding values for Arg50 amd Arg52 are 0.73 and 0.63, respectively, at pH 5.0, thus confirming that the two arginines are rigid and hydrogen bonded. At pH 2.5, these hydrogen bonds are still retained with Arg50 appearing to be more restrained (S2 = 0.71) than Arg52 (S2 = 0.56). This is consistent a greater contribution by Arg50 to the conformational stability of the reactive-site loop in CMTI-V. The results also indicate that the Arg50 and Arg52 side chains are not hydrogen-bonded to carboxylate groups, which would be protonated at pH 2.5 and, hence, unavailable for hydrogen-bonding interactions. The overall folding of rCMTI-V appears not to be significantly affected by the pH change, as indicated by comparisons of 1H and 15N chemical shifts, sequential NOE cross-peaks, and S2 values of the backbone atoms, and the conserved side-chain dynamics of Trp9 and Trp54--residues that are involved in hydrophobic and hydrogen-bonding interactions with others in the protein core and the binding loop, respectively.

Solution structure and backbone dynamics of recombinant Cucurbita maxima trypsin inhibitor-V determined by NMR spectroscopy

The solution structure of recombinant Cucurbita maxima trypsin inhibitor-V (rCMTI-V), whose N-terminal is unacetylated and carries an extra glycine residue, was determined by means of two-dimensional (2D) homo and 3D hetero NMR experiments in combination with a distance geometry and simulated annealing algorithm. A total of 927 interproton distances and 123 torsion angle constraints were utilized to generate 18 structures. The root mean squared deviation (RMSD) of the mean structure is 0.53 A for main-chain atoms and 0.95 A for all the non-hydrogen atoms of residues 3-40 and 49-67. The average structure of rCMTI-V is found to be almost the same as that of the native protein [Cai, M., Gong, Y., Kao, J.-L., & Krishnamoorthi, R. (1995) Biochemistry 34, 5201-5211]. The backbone dynamics of uniformly 15N-labeled rCMTI-V were characterized by 2D 1H-15N NMR methods. 15N spin-lattice and spin-spin relaxation rate constants (R1 and R2, respectively) and [1H]-15N steady-state heteronuclear Overhauser effect enhancements were measured for the peptide NH units and, using the model-free formalism [Lipari, G., & Szabo, A. (1982) J. Am. Chem. Soc. 104, 4546-4559, 4559-4570], the following parameters were determined: overall tumbling correlation time for the protein molecule (tau m), generalized order parameters for the individual N-H vectors (S2), effective correlation times for their internal motions (tau e), and terms to account for motions on a slower time scale (second) due to chemical exchange and/or conformational averaging (R(ex)). Most of the backbone NH groups of rCMTI-V are found to be highly constrained ((S2) = 0.83) with the exception of those in the binding loop (residues 41-48, (S2) = 0.71) and the N-terminal region ((S2) = 0.73). Main-chain atoms in these regions show large RMSD values in the average NMR structure. Residues involved in turns also appear to have more mobility ((S2) = 0.80). Dynamical properties of rCMTI-V were compared with those of two other inhibitors of the potato I family--eglin c [Peng, J. W., & Wagner, G. (1992) Biochemistry 31, 8571-8586] and barley chymotrypsin inhibitor 2 [CI-2; Shaw, G. L., Davis, B., Keeler, J., & Fersht, A. R. (1995) Biochemistry 34, 2225-2233]. The Cys3-Cys48 linkage found only in rCMTI-V appears to somewhat reduce the N-terminal flexibility; likewise, the C-terminal of rCMTI-V, being part of a beta-sheet, appears to be more rigid.

Reactive-site hydrolyzed Cucurbita maxima trypsin inhibitor-V: function, thermodynamic stability, and NMR solution structure

Reactive-site (Lys44-Asp45 peptide bond) hydrolyzed Cucurbita maxima trypsin inhibitor-V (CMTI-V*) was prepared and characterized: In comparison to the intact form, CMTI-V* exhibited markedly reduced inhibitory properties and binding affinities toward trypsin and human blood coagulation factor XIIa. The equilibrium constant of trypsin-catalyzed hydrolysis, Khyd, defined as [CMTI-V*]/[CMTI-V], was measured to be approximately 9.4 at 25 degrees C (delta G degrees = -1.3 kcal.mol-1). From the temperature dependence of delta G degrees, the following thermodynamic parameters were estimated: delta H degrees = 1.6 kcal.mol-1 and delta S degrees = 9.8 eu. In order to understand the functional and thermodynamic differences between the two forms, the three-dimensional solution structure of CMTI-V* was determined by a combined approach of NMR, distance geometry, and simulated annealing methods. Thus, following sequence-specific and stereospecific resonance assignments, including those of beta-, gamma-, delta-, and epsilon-hydrogens and valine methyl hydrogens, 809 interhydrogen distances and 123 dihedral angle constraints were determined, resulting in the computation and energy-minimization of 20 structures for CMTI-V*. The average root mean squared deviation in position for equivalent atoms between the 20 individual structures and the mean structure obtained by averaging their coordinates is 0.67 +/- 0.15 A for the main chain atoms and 1.19 +/- 0.23 A for all the non-hydrogen atoms of residues 5-40 and residues 48-67.(ABSTRACT TRUNCATED AT 250 WORDS)

Solution conformations of proline rings in proteins studied by NMR spectroscopy

Three different conformations of proline rings in a protein in solution, Up, Down and Twist, have been distinguished, and stereospecific assignments of the pyrrolidine beta-, gamma- and delta-hydrogens have been made on the basis of 1H-1H vicinal coupling constant patterns and intraresidue NOEs. For all three conformations, interhydrogen distances in the pairs alpha-beta 3, beta 3-gamma 3, beta 2-gamma 2, gamma 2-delta 2, and gamma 3-delta 3 (2.3 A) are shorter than those in the pairs alpha-beta 2, beta 2-gamma 3, beta 3-gamma 2, gamma 2-delta 3, and gamma 3-delta 2 (2.7-3.0 A), resulting in stronger NOESY cross peaks. For the Up conformation, the beta 3-gamma 2 and gamma 2-delta 3 spin-spin coupling constants are small (< 3 Hz), and weak cross peaks are obtained in a short-mixing-time (10 ms) TOCSY spectrum; all other vicinal coupling constants are in the range 5-12 Hz, and result in medium to strong TOCSY cross peaks. For the Down form, the alpha-beta 2, beta 2-gamma 3, and gamma 3-delta 2 vicinal coupling constants are small, leading to weak TOCSY cross peaks; all other couplings again are in the range 5-12 Hz, and result in medium to strong TOCSY cross peaks. In the case of a Twist conformation, dynamically averaged coupling constants are anticipated. The procedure has been applied to bovine pancreatic trypsin inhibitor and Cucurbita maxima trypsin inhibitor-V, and ring conformations of all prolines in the two proteins have been determined.

A practical method for stereospecific assignments of gamma- and delta-methylene hydrogens via estimation of vicinal 1H-1H coupling constants

Stereospecific assignments are made for gamma- and delta-methylene hydrogens in a protein by means of estimation of vicinal 1H-1H spin-spin coupling constants from a short-mixing-time TOCSY experiment. 3J alpha beta coupling constants, as measured from a P.E. COSY map, are shown to be well correlated with alpha-beta cross-peak intensities of a short-mixing-time (10 ms) TOCSY map. The procedure is illustrated by application to a trypsin-inhibitor protein (M(r) approximately 7 Kd). Thus, gamma-methylene hydrogens of isoleucine residues have been stereospecifically assigned on the basis of 3J beta gamma 1H-1H coupling patterns and intraresidue cross-peak intensities in a NOESY map; gamma-hydrogens of other residues, such as lysine and arginine, have been stereospecifically assigned solely on the basis of cross-peak intensity patterns resulting from coupling of two beta-hydrogens to two gamma-hydrogens, and in conjunction with stereospecific assignments of beta-methylene hydrogens. However, intraresidue NOE intensities are needed if one or two pairs of coupling constants cannot be estimated because of cross peaks either overlapping or occurring proximal to the diagonal. The delta-methylene hydrogens have been stereospecifically assigned on the basis of coupling between two gamma-hydrogens and two delta-hydrogens, in combination with stereospecific assignments of gamma-hydrogens. Stereospecific assignments of side chains should contribute to the overall precision and accuracy of NMR-determined three-dimensional solution structures of proteins.

Three-dimensional solution structure of Cucurbita maxima trypsin inhibitor-V determined by NMR spectroscopy

The solution structure of Cucurbita maxima trypsin inhibitor-V (CMTI-V), which is also a specific inhibitor of the blood coagulation protein, factor XIIa, was determined by 1H NMR spectroscopy in combination with a distance-geometry and simulated annealing algorithm. Sequence-specific resonance assignments were made for all the main-chain and most of the side-chain hydrogens. Stereospecific assignments were also made for some of the beta-, gamma-, delta-, and epsilon-hydrogens and valine methyl hydrogens. The ring conformations of all six prolines in the inhibitor were determined on the basis of 1H-1H vicinal coupling constant patterns; most of the proline ring hydrogens were stereospecifically assigned on the basis of vicinal coupling constant and intraresidue nuclear Overhauser effect (NOE) patterns. Distance constraints were determined on the basis of NOEs between pairs of hydrogens. Dihedral angle constraints were determined from estimates of scalar coupling constants and intraresidue NOEs. On the basis of 727 interproton distance and 111 torsion angle constraints, which included backbone phi angles and side-chain chi 1, chi 2, chi 3, and chi 4 angles, 22 structures were calculated by a distance geometry algorithm and refined by energy minimization and simulated annealing methods. Both main-chain and side-chain atoms are well-defined, except for a loop region, two terminal residues, and some side-chain atoms located on the molecular surface. The average root mean squared deviation in the position for equivalent atoms between the 22 individual structures and the mean structure obtained by averaging their coordinates is 0.58 +/- 0.06 A for the main-chain atoms and 1.01 +/- 0.07 A for all the non-hydrogen atoms of residues 3-40 and 49-67. These structures were compared to the X-ray crystallographic structure of another protein of the same inhibitor family-chymotrypsin inhibitor-2 from barley seeds [CI-2; McPhalen, C. A., & James, M. N. G. (1987) Biochemistry 26, 261-269]. The main-chain folding patterns are highly similar for the two proteins, which possess 62% sequence differences. However, major differences are noted in the N- and C-terminal segments, which may be due to the presence of a disulfide bridge in CMTI-V, but not in CI-2.

Changing the inhibitory specificity and function of Cucurbita maxima trypsin inhibitor-V by site-directed mutagenesis

Cucurbita maxima trypsin inhibitor-V (CMTI-V) is also a specific inhibitor of human blood coagulation factor beta-factor XIIa. A recombinant version of CMTI-V has allowed probing of roles of individual amino acid residues including the reactive site residue, lysine (P1), by site-directed mutagenesis. The K44R showed at least a 5-fold increase in inhibitory activity toward human beta-factor XIIa, while there was no change toward bovine trypsin. This result demonstrates that beta-factor-XIIa prefers an arginine residue over lysine residue, while trypsin is non-specific to lysine or arginine in its binding pocket. On the other hand, the specificity of CMTI-V could be changed from trypsin to chymotrypsin inhibition by mutation of the P1 residue to either leucine or methionine (K44L or K44M).

1H NMR investigation of the heme cavity of elephant (E7 Gln) met-cyano-myoglobin. Evidence for a B-helix phenylalanine interaction with bound ligand

A combination of one- and two-dimensional NMR experiments has been used to identify and spatially locate the heme pocket residues in the paramagnetic, low spin, met-cyano complex of elephant myoglobin. In addition to assigning resonances of the conserved residues, we have also assigned Gln64 (E7) and an aromatic ring designated PheA whose side chain is inserted into the heme pocket, as found earlier for elephant carbonmonoxy-myoglobin and oxy-myoglobin (Yu, L. P., La Mar, G. N., and Mizukami, H. (1990) Biochemistry 29, 2578-2585). The assigned conserved proximal side residues (Leu89(F4), Ala90(F5), His93(F8), His97(FG3), Ile99(FG5), Leu104(G5), Phe138(H15), and Tyr146(H23)) and conserved distal side residues (Phe43(CD1), Thr67(E10), Val68(E11), and Ala71(E14)) in elephant met-cyano-myoglobin are found to have orientations similar to those in sperm whale met-cyano-myoglobin. The observed dipolar connectivities and dipolar shift pattern for the substituted Gln64(E7) place the Gln in the heme pocket oriented toward the iron, as found for His64(E7). The conserved structural elements demand that the inserted PheA originate from the B-helix (i.e. Phe27 or Phe33). Dipolar contacts between the inserted PheA and the conserved residues Phe43(CD1), Val68(E11), Ile107(G8), and Gln64(E7), place PheA in the position occupied by the B10 residue in sperm whale myoglobin (Mb), with the larger size of the PheA side chain as compared to the replaced Leu being accommodated by the vacancy that occurs in sperm whale Mb. The paramagnetic induced relaxation places PheA in van der Waals contact with the bound ligand. Hence we conclude that the B10 position of elephant Mb is occupied by a Phe, and this substitution relative to sperm whale Mb is responsible for the low autoxidation rate and low reduction potential of elephant Mb. A reduced autoxidation rate has been reported for a sperm whale synthetic point mutant Leu29(B10) --> Phe (Carver, T. E., Brantley, R. E., Jr., Singleton, E. W., Arduini, R. M., Quillin, M. L., Phillips, G. N., and Olson, J. S. (1992) J. Biol. Chem. 267, 14443-14450). The published sequence of elephant Mb places B-helix Phe residues at position 27(B8) and 33(B14), but a Phe at neither of these positions can account for the observed NMR properties. Since a large proportion of the substitutions in elephant relative to sperm whale Mb, and some of the least conservative, occur in the B-helix, neither a structurally perturbed B-helix nor an error in the sequence can be discounted.

Chemical synthesis, molecular cloning, overexpression, and site-directed mutagenesis of the gene coding for pumpkin (Curcubita maxima) trypsin inhibitor CMTI-V

The gene encoding for a pumpkin (Curcubita maxima) trypsin inhibitor CMTI-V was synthesized chemically. The synthetic gene was prepared from four overlapping oligonucleotides by overlapping extension. The synthetic gene was amplified by polymerase chain reaction, cloned into a T7 expression vector and expressed in Escherichia coli as a fusion protein. The clone, namely 70-1, encoded a fusion protein containing 7 amino acid residues of the N-terminus of the bacterial protein rho 10 and the entire 68 residues of CMTI-V. The wild-type fusion protein constituted approximately 15% of the total bacterial protein mass and was purified to homogeneity in a single step by antibody affinity chromatography. The wild-type fusion protein possesses inhibitory activity toward trypsin and beta-Factor XIIa, but to a lesser extent when compared to the natural CMTI-V. A mutant, T43A, in which threonine at position 43 (P2 position) was replaced by alanine, was constructed. This mutant showed considerably lower specific inhibitory activity toward both trypsin and beta-Factor XIIa.

Natural abundance 15N NMR assignments delineate structural differences between intact and reactive-site hydrolyzed Cucurbita maxima trypsin inhibitor III

15N NMR assignments were made to the backbone amide nitrogen atoms at natural isotopic abundance of intact and reactive-site (Arg5-Ile6) hydrolyzed Cucurbita maxima trypsin inhibitor III (CMTI-III and CMTI-III*, respectively) by means of 2D proton-detected heteronuclear single bond chemical shift correlation (HSBC) spectroscopy, utilizing the previously made sequence-specific 1H NMR assignments (Krishnamoorthi et al. (1992) Biochemistry 31, 898-904). Comparison of the 15N chemical shifts of the two forms of the inhibitor molecule revealed significant changes not only for residues located near the reactive-site region, but also for those distantly located. Residues Cys3, Arg5, Leu7, Met8, Cys10, Cys16, Glu19, His25, Tyr27, Cys28 and Gly29 showed significant chemical shift changes ranging from 0.3 to 6.1 ppm, thus indicating structural perturbations that were transmitted throughout the molecule. These findings confirm the earlier conclusions based on 1H NMR investigations.

Structural consequences of the natural substitution, E9K, on reactive-site-hydrolyzed squash (Cucurbita maxima) trypsin inhibitor (CMTI), as studied by two-dimensional NMR

Sequence-specific hydrogen-1 NMR assignments were made to all of the 29 amino acid residues of reactive-site-hydrolyzed Cucurbita maxima trypsin inhibitor I (CMTI-I*) by the application of two-dimensional NMR (2D NMR) techniques, and its secondary structural elements (two tight turns, a 3(10)-helix, and a triple-stranded beta-sheet) were identified on the basis of short-range NOESY cross peaks and deuterium-exchange kinetics. These secondary structural elements are present in the intact inhibitor [Holak, T. A., Gondol, D., Otlewski, J., & Wilusz, T. (1989) J. Mol. Biol. 210, 635-648] and are unaffected by the hydrolysis of the reactive-site peptide bond between Arg5 and Ile6, in accordance with the earlier conclusion reached for CMTI-III* [Krishnamoorthi, R., Gong, Y.-X., Lin, C. S., & VanderVelde, D. (1992) Biochemistry 31, 898-904]. Chemical shifts of backbone hydrogen atoms, peptide NH's, and C alpha H's, of CMTI-I* were compared with those of the intact inhibitor, CMTI-I, and of the reactive-site-hydrolyzed, natural, E9K variant, CMTI-III*. Cleavage of the Arg5-Ile6 peptide bond resulted in changes of chemical shifts of most of the backbone atoms of CMTI-I, in agreement with the earlier results obtained for CMTI-III. Comparison of chemical shifts of backbone hydrogen atoms of CMTI-I* and CMTI-III* revealed no changes, except for residues Glu9 and His25. However, the intact forms of the same two proteins, CMTI-I and CMTI-III, showed small but significant perturbations of chemical shifts of residues that made up the secondary structural elements of the inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Two-dimensional NMR studies of squash family inhibitors. Sequence-specific proton assignments and secondary structure of reactive-site hydrolyzed Cucurbita maxima trypsin inhibitor III

The solution structure of reactive-site hydrolyzed Cucurbita maxima trypsin inhibitor III (CMTI-III*) was investigated by two-dimensional proton nuclear magnetic resonance (2D NMR) spectroscopy. CMTI-III*, prepared by reacting CMTI-III with trypsin which cleaved the Arg5-Ile6 peptide bond, had the two fragments held together by a disulfide linkage. Sequence-specific 1H NMR resonance assignments were made for all the 29 amino acid residues of the protein. The secondary structure of CMTI-III*, as deduced from NOESY cross peaks and identification of slowly exchanging hydrogens, contains two turns (residues 8-12 and 24-27), a 3(10)-helix (residues 13-16), and a triple-stranded beta-sheet (residues 8-10, 29-27, and 21-25). This secondary structure is similar to that of CMTI-I [Holak, T. A., Gondol, D., Otlewski, J., & Wilusz, T. (1989) J. Mol. Biol. 210, 635-648], which has a Glu instead of a Lys at position 9. Sequential proton assignments were also made for the virgin inhibitor, CMTI-III, at pH 4.71, 30 degrees C. Comparison of backbone hydrogen chemical shifts of CMTI-III and CMTI-III* revealed significant changes for residues located far away from the reactive-site region as well as for those located near it, indicating tertiary structural changes that are transmitted through most of the 29 residues of the inhibitor protein. Many of these residues are functionally important in that they make contact with atoms of the enzyme in the trypsin-inhibitor complex, as revealed by X-ray crystallography [Bode, W., Greyling, H. J., Huber, R., Otlewski, J., & Wilusz, T. (1989) FEBS Lett. 242, 285-292].(ABSTRACT TRUNCATED AT 250 WORDS)

Proton NMR studies of Cucurbita maxima trypsin inhibitors: evidence for pH-dependent conformational change and His25-Tyr27 interaction

A pH-dependent His25-Tyr27 interaction was demonstrated in the case of Cucurbita maxima trypsin inhibitors (CMTI-I and CMTI-III) by means of nuclear magnetic resonance (NMR) spectroscopy. pH titration, line widths, peak shapes, deuterium exchange kinetics, and two-dimensional nuclear Overhauser effect spectroscopy (NOESY) were employed to characterize a conformational change involving Tyr27, which was shown to be triggered by deprotonation of His25 around pH 6. A hydrogen bond is proposed to be formed between N epsilon of His25 and OH of Tyr27, as a distance between the atoms, His25 N epsilon and Tyr27 OH, of 3.02 A is consistent with a model built with NOE-derived distance constraints. Both the X-ray [Bode, W., Greyling, J.H., Huber, R., Otlewski, J., & Wilusz, T. (1989) FEBS Lett. 242, 282-292] and NMR [Holak, T.A., Gondol, D., Otlewski, J., & Wilusz, T. (1989) J. Mol. Biol. 210, 635-648] structures of CMTI-I at low pH (4.7-5.3) rule out such an interaction between the two aromatic rings, as the ring planes are oriented about 10 A away from each other. The presently characterized relative orientations of His25 and Tyr27 are of functional significance, as these residues make contact with the enzyme in the enzyme-inhibitor complex. Furthermore, trypsin assay and inhibitor-binding studies showed that conformations of trypsin and the squash inhibitor were functionally relevant only in the pH range 6-8. The pKa of His25 was determined and found to be influenced by Glu9/Lys substitution and by the hydrolysis of the reactive-site peptide bond between Arg5 and Ile6.(ABSTRACT TRUNCATED AT 250 WORDS)

A new protein inhibitor of trypsin and activated Hageman factor from pumpkin (Cucurbita maxima) seeds

A protein inhibitor (CMTI-V; Mr 7106) of trypsin and activated Hageman factor (Factor XIIa), a serine protease involved in blood coagulation, has been isolated for the first time from pumpkin (Cucurbita maxima) seeds by means of trypsin-affinity chromatography and reverse phase high performance liquid chromatography (HPLC). The dissociation constants of the inhibitor complexes with trypsin and Factor XIIa have been determined to be 1.6 x 10(-8) and 4.1 x 10(-8) M, respectively. The primary structure of CMTI-V is reported. The protein has 68 amino acid residues and one disulfide bridge and shows a high level of sequence homology to the Potato I inhibitor family. Furthermore, its amino terminus consists of an N-acetylates Ser. The reactive site has been established to be the peptide bond between Lys44-Asp45. The modified inhibitor which has the reactive site peptide bond hydrolyzed inhibits trypsin but not the Hageman factor.

1H-NMR studies of high-potential iron-sulfur protein from the purple phototrophic bacterium, Rhodospirillum tenue

The high-potential iron-sulfur protein (HiPIP) from Rhodospirillum tenue (strain 3761) shows only a weak (20-25%) sequence similarity to HiPIPs from Chromatium vinosum, Ectothiorhodospira halophila and Ectothiorhodospira vacuolata, including the strict conservation of only two of the twelve residues assumed to be in the 4Fe-4S cluster packing region [Tedro, S. M., Meyer, T. E. and Kamen, M. D. (1979) J. Biol. Chem. 254, 1495-1500]. In spite of these differences, the general range and distribution of hyperfine-shifted 1H-NMR peaks of oxidized and reduced R. tenue HiPIP resemble those of E. halophila HiPIP I [Krishnamoorthi, R., Markley, J. L., Cusanovich, M. A., Pryzycieki, C. T. and Meyer, T. E. (1986) Biochemistry 25, 60-67]. Temperature- and pH-dependence and longitudinal relaxation behavior were determined for hyperfine-shifted peaks of the oxidized protein. Tentative assignments of peaks to ligands and aromatic residues suggest the presence of common apoprotein-active-site interactions in these proteins. Differences occur in the pattern of paramagnetically shifted peaks attributed to hydrogens bonded to the 4Fe-4S cluster. Hyperfine-shifted peaks of R. tenue HiPIP are not perturbed by pH changes in the range 5-9. In contrast, those of the C. vinosum protein exhibit a pH-dependence of chemical shifts that has been attributed to the titration of His42 [Nettesheim, D. G., Meyer, T. E., Feinberg, B. A. and Otvos, J. D. (1983) J. Biol. Chem. 258, 8235-8239]. Since R. tenue HiPIP contains no histidine, the present observation confirms the above hypothesis.