Preparation of environmentally friendly, high strength, adhesion and stability hydrogel based on lignocellulose framework

Hydrogels are extensively utilized in the fields of electronic skin, environmental monitoring, biological dressings due to their excellent flexibility and conductivity. However, traditional hydrogel materials possess drawbacks such as environmental toxicity, low strength, poor stability, and water loss deactivation, which limited its frequent applications. Here, a flexible conductive hydrogel called wood-based DES hydrogel (WDH) with high strength, high adhesion, high stability, and high sensitivity was successfully synthesized by using environmentally friendly lignocellulose as skeleton and deep eutectic solvent as matrix. The strength of WDH prepared from lignocellulose framework is approximately 50 times higher than poly deep eutectic solvent hydrogel, and about 4.5 times higher than that prepared from cellulose skeleton. The WDH exhibits stable adhesion to most common materials and demonstrates exceptional dimensional stability. Its conductivity remains unaffected by water, even after prolonged exposure to air, maintaining a value of 0.0245 S/m. The anisotropy inherent in the system results in three distinct linear sensing intervals for WDH, exhibiting a maximum sensitivity of 5.45. This paper verified the advantages of lignocellulose framework in improving the strength and stability of hydrogels, which provided a new strategy for the development of sensor materials.

High-Strength, High-Swelling-Resistant, High-Sensitivity Hydrogel Sensor Prepared with Wood That Retains Lignin

Wood-derived hydrogels possess satisfactory longitudinal strength but lack excellent swelling resistance and dry shrinkage resistance when achieving high anisotropy. In this study, we displayed the preparation of highly dimensional stable wood/polyacrylamide hydrogels (wood/PAM-Al3+). The alkali-treated wood retains lignin as the skeleton of the hydrogel. Second, Al ions were added to the metal coordination with lignin. Finally, by employing free radical polymerization, we construct a conductive electronic network using polyaniline within the wood/PAM-Al3+ matrix to create the flexible sensor. This approach leverages lignin's integrated structure within the middle lamella to provide enhanced swelling resistance and stronger binding strength in the transverse direction. Furthermore, coordination between lignin and Al ions improves the mechanical strength of the wood hydrogel. Polyaniline provides stable linear pressure and temperature responses. The wood/PAM-Al3+ exhibits a transverse swelling ratio of 3.90% while achieving a longitudinal tensile strength of 20.5 MPa. This high-strength and high-stability sensor is capable of monitoring macroscale human behavior. Therefore, this study presents a simple yet innovative strategy for constructing tough hydrogels while also establishing an alternative pathway for exploring lignin networks in new functional materials development.

Near Infrared Spectroscopy for Prediction of Yeast and Mould Counts in Black Soldier Fly Larvae, Feed and Frass: A Proof of Concept

The use of black soldier fly larvae (BSFL) grown on different organic waste streams as a source of feed ingredient is becoming very popular in several regions across the globe. However, information about the easy-to-use methods to monitor the safety of BSFL is a major step limiting the commercialization of this source of protein. This study investigated the ability of near infrared (NIR) spectroscopy combined with chemometrics to predict yeast and mould counts (YMC) in the feed, larvae, and the residual frass. Partial least squares (PLS) regression was employed to predict the YMC in the feed, frass, and BSFL samples analyzed using NIR spectroscopy. The coefficient of determination in cross validation (R2CV) and the standard error in cross validation (SECV) obtained for the prediction of YMC for feed were (R2cv: 0.98 and SECV: 0.20), frass (R2cv: 0.81 and SECV: 0.90), larvae (R2cv: 0.91 and SECV: 0.27), and the combined set (R2cv: 0.74 and SECV: 0.82). However, the standard error of prediction (SEP) was considered moderate (range from 0.45 to 1.03). This study suggested that NIR spectroscopy could be utilized in commercial BSFL production facilities to monitor YMC in the feed and assist in the selection of suitable processing methods and control systems for either feed or larvae quality control.

Evaluation of the fermentation potential of lactic acid bacteria isolated from herbs, fruits and vegetables as starter cultures in nut-based milk alternatives

Fermentation of plant-based milk alternatives (PBMAs), including nut-based products, has the potential to generate new foods with improved sensorial properties. In this study, we screened 593 lactic acid bacteria (LAB) isolates from herbs, fruits and vegetables for their ability to acidify an almond-based milk alternative. The majority of the strongest acidifying plant-based isolates were identified as Lactococcus lactis, which were found to lower the pH of almond milk faster than dairy yoghurt cultures. Whole genome sequencing (WGS) of 18 plant-based Lc. lactis isolates revealed the presence of sucrose utilisation genes (sacR, sacA, sacB and sacK) in the strongly acidifying strains (n = 17), which were absent in one non-acidifying strain. To confirm the importance of Lc. lactis sucrose metabolism in efficient acidification of nut-based milk alternatives, we obtained spontaneous mutants defective in sucrose utilisation and confirmed their mutations by WGS. One mutant containing a sucrose-6-phosphate hydrolase gene (sacA) frameshift mutation was unable to efficiently acidify almond, cashew and macadamia nut milk alternatives. Plant-based Lc. lactis isolates were heterogeneous in their possession of the nisin gene operon near the sucrose gene cluster. The results of this work show that sucrose-utilising plant-based Lc. lactis have potential as starter cultures for nut-based milk alternatives.

Radial extracorporeal shock wave therapy alleviates acute inflammation of human primary tenocytes through the integrin-FAK-p38MAPK pathway

OBJECTIVES

To explore whether radial extracorporeal shock wave therapy (rESWT) can alleviate acute inflammation of human primary tenocytes by the integrin-focal adhesion kinase (FAK)-p38 mitogen-activated protein kinase (MAPK) pathway.

METHODS

Western blotting was used to evaluate the changes in the integrin-FAK-p38MAPK signaling pathway mediated by rESWT using specific antibodies targeting the phosphorylation sites of intracellular signal pathway proteins.

RESULTS

rESWT up-regulated FAK phosphorylation and down-regulated p38MAPK phosphorylation levels in a tumor necrosis factor (TNF)-α-induced acute inflammation model of human primary tenocytes. Pretreatment with an integrin inhibitor significantly reduced rESWT-mediated downregulation of p38MAPK phosphorylation and attenuated its reversal effect on the increased secretion of pro-inflammatory cytokines in TNF-α-induced human primary tenocytes.

CONCLUSIONS

Our results imply that rESWT may partially alleviate acute inflammation in human primary tenocytes through the integrin-FAK-p38MAPK pathway.

Ultra-Thin Wood-Based Acoustic Diaphragms Fabricated via an Environmentally Friendly Strategy

An acoustic diaphragm is a crucial component that regulates sound quality in earphones and loudspeakers. Natural wood with inherent good acoustic resonance and vibration spectrum is widely used in sound devices. However, using natural wood to produce an acoustic diaphragm is still a big challenge because making ultra-thin wood is hard and it warps easily. Therefore, this study introduces a new method for preparing ultra-thin wood acoustic diaphragms less than 10 μm in thickness, relying on delignification, sulfonation, and densifying techniques. The innovative sulfonation process increased the intermolecular hydrogen bond force, which significantly improved the tensile strength and Young's modulus of the wood diaphragm, up to 195 MPa and 27.1 GPa, respectively. Compared with the commonly used diaphragms in the market, this wood diaphragm exhibits an excellent specific dynamic elastic modulus up to 95.1 GPa/g cm³, indicating better acoustic properties. Also, the resonance frequency was up to 1240 Hz, 4.5 times higher than the titanium diaphragm among high-end products. Besides, the drying shrinkage rate of the ultra-thin wood diaphragm is only 1.2%, indicating excellent dimensional stability. This high-quality wood acoustic diaphragm has a very high application prospect and outstanding attributes for promoting the development of acoustic devices. Moreover, the reaction reagent can be recycled after preparation, and the selected reagents are green and environmentally friendly.

Modernising physician resource planning: a national interactive web platform for Canadian medical trainees

Background

Healthcare systems rely heavily upon human resources to ensure high-quality access to care for the general population. With significant health worker shortages predicted worldwide in the coming decades, maximizing the current workforce by means of a physician resource planning (PRP) strategy that ensures the right number, mix, and distribution of physicians to meet population needs is warranted. In Canada, there is an insufficient number of primary care providers, and disproportionately low numbers of specialist physicians in rural compared to urban regions. Currently, Canadian medical students are not effectively included in PRP strategy and lack the required information for career orientation to help rebalance the population’s workforce needs. This paper present the Health Human Resource (HHR) Platform, a comprehensive web tool that includes relevant workforce data to empower medical students in choosing a discipline based on both personal interests and social accountability.

Results

Physician workforce data, comments from Canadian residency program directors, and career planning resources were collected by the Canadian Federation of Medical Student’s (CFMS) HHR Task Force. This information was consolidated to create a national interactive platform that uses a map, comparison table, and trend graphs to illustrate over 500,000 unique data points from 37 datasets, including specific information and resources spanning 62 medical specialties from 2015 onwards. There was a 24.6% response rate for program director comments. During the first 4 months of the HHR Platform launch, there were 2434 different users, of which 985 were returning, with an average of 20.0 users per day spending on average 3 min on the platform.

Conclusions

The HHR Platform constitutes a national approach to PRP informing medical students on the mix and distribution of physicians needed to meet the future healthcare demands of the Canadian population.

Genomic epidemiology of Corynebacterium striatum from three regions of China: an emerging national nosocomial epidemic

BACKGROUND

Corynebacteritum straitum has been considered as an emerging multi-drug-resistant (MDR) pathogen. Isolation of MDR C. striatum as the only organism from respiratory samples from hospitalized patients is increasing in China.

AIM

To elucidate the genomic epidemiology and evolution of C. striatum in China.

METHODS

A total of 260 isolates from 2016 to 2018 were collected from three hospitals in three regions of China. Antibiotic sensitivity testing was performed on all isolates. Whole-genome sequencing was applied to all isolates to assess their genomic diversity and relationships and detect the presence of antimicrobial resistance genes (ARG) and ARG cassettes.

FINDINGS

Almost all isolates (96.2%, 250/260) showed multi-drug-resistance. Genome sequencing revealed four major lineages with lineage IV emerging as the epidemic lineage. Most of the diversity was developed in the last 6 years. Each hospital has its own predominant clones with potential spread between Hebei and Guangdong hospitals. Genomic analysis further revealed multiple antimicrobial resistance genes.

CONCLUSIONS

Our results suggested that four lineages of C. striatum have spread in parallel across China, causing persistent and extensive transmissions within hospitals. MDR C. striatum infection has become a national epidemic. Antibiotic-driven selection pressure may have played significant roles in forming persistent and predominant clones. Our data provide the basis for surveillance and prevention strategies to control the epidemic caused by MDR C. striatum.

Isolation and Evaluation of Anti-Listeria Lactococcus lactis from Vegetal Sources

This chapter describes methods used to isolate, identify, and partially characterize lactic acid bacteria (LAB) which exhibit inhibitory activity against Listeria monocytogenes from foods. Vegetal (plant based) sources are rich in naturally occurring LAB and therefore provide an easily accessible source of strains with potential antimicrobial activity for use in food-processing applications. From our previous work, the majority of LAB with inhibitory activity against L. monocytogenes were identified as generally recognized as safe (GRAS) Lactococcus lactis. Although these bacteria are most commonly known for their role in industrial dairy fermentations, they are believed to have originally derived from natural plant-based habitats. These isolates with anti-Listeria activity were all found to carry the genes involved in the production of nisin, which is an approved food-grade preservative (E234). These isolates may find various applications for in situ production of nisin allowing control of L. monocytogenes in various fermented and non-fermented foods and other environments.

A160 THE EFFECT OF AN INSTRUCTIVE VIDEO ON THE BOWEL PREPARATION EXPERIENCE

Background

Over 26000 new cases of colorectal cancer (CRC) are diagnosed each year in Canada. This number has been decreased significantly by the implementation of CRC screening that includes removal of any polyps found during colonoscopies. Despite this, approximately 1 in 4 colonoscopies are inadequate for the detection of early neoplasms due to insufficient bowel preparation prior to the colonoscopy. Consequently, there is a need to improve patient adherence to the bowel preparation protocol. Previous research has shown that enhanced education, including the methods and rationale for bowel preparation prior to a colonoscopy, improves the quality of the bowel preparation.

Aims

We hypothesised that patients with access to a replayable video explaining the bowel preparation protocol and its importance would have increased satisfaction and noninferior bowel preparations.

Methods

100 patients undergoing programmatic screening colonoscopy were randomly assigned into one of two groups. The control group was given the standard presentation currently given to patients. The experimental group was given the same presentation and also given access to an educational video. This video is based on Alberta provincial bowel preparations which have been tested and evaluated. Participants in both groups were sent a survey one day after their colonoscopy. Subjects completed a modified version of the Outpatient and Ambulatory Surgery Consumer Assessment of Healthcare Providers and Systems survey with added questions designed to assess their satisfaction with the education they received on the bowel preparation. Bowel preparation quality was assessed on a 4-point Likert scale by the endoscopist.

Results

17 participants (10 female), aged 40–72 (Mage = 60) have enrolled in the study thus far; however, most have yet to have their colonoscopy. Initial results revealed that all participants had high levels of satisfaction with the presentation they were given. Those in the control group indicated that they would have liked to have had access to a video guide to the bowel preparation before their procedure. The participant in the experimental group indicated high levels of satisfaction with this video, noting that it provided important information not available from other sources. Information on the quality of their bowel preparations is pending.

Conclusions

The use of multimedia explanations of the bowel preparation has promise in improving patient satisfaction with the bowel preparation. Further studies may guide best methods for implementing a video assisted educational model to enhance colonoscopy preparation.

Funding Agencies

The first author received an Edna Wakefield Rowe Memorial Summer Research Award from the Faculty of Medicine & Dentistry at the University of Alberta to support this work.

P1019Validation of a risk score to predict the need for pacemaker implantation after transcatheter aortic valve replacement

Background

New conduction abnormalities necessitating pacemaker implantation (PMI) is a common occurrence after TAVR. There is an increased rate of PMI in the those receiving the most contemporary implanted valve, the Edwards Sapien-3 (S3), compared to prior generation balloon expandable valves. We previously described predictors of PMI in a large cohort. Herein we sought to validate these predictors of PMI in a subsequent validation cohort.

Methods

We evaluated all patients undergoing first time elective TAVR with S3 at our institution (n=326). We developed a risk score based on a predictive model we have previously described. Patients received one point for each of the following: history of syncope, oversizing of the valve >16%, baseline right bundle branch block morphology, and two points for a QRS duration >115 ms. We performed regression analysis of the risk score and need for PMI. We also evaluated the performance of the risk score using ROC analysis.

Results

Thirty patients (8%) of the total cohort had need for PMI after S3 implantation. Those with PMI had a higher rate of pre-existing infra-nodal conduction system disease – including QRS duration >115ms (57% vs. 20%, p<0.001) and right bundle branch block (RBBB) morphology (47% vs. 10%, p<0.001) - as well as more frequent valve oversizing >15.7% (47% vs. 23%, p<0.01). There was no significant difference in a history of syncope (10% vs. 8%, p=0.72) between groups. The PMI risk score had an area under the curve of 0.753 on ROC analysis. The PMI risk score was significantly associated with PMI (OR 2.37; 95% CI [1.64–3.34], p<0.001).

Rate of PMI Stratified by Risk Score

Conclusions

The PMI risk score was strongly predictive of the need for PMI after implantation of the S3 valve in a large validation cohort. The PMI risk score performed well in sensitivity analysis. This PMI risk score represents a simple tool to help further risk stratify patients being considered for TAVR.

Translation and validation of a Chinese version of the Warwick-Edinburgh Mental Well-being Scale with undergraduate nursing trainees

WHAT IS KNOWN ON THE SUBJECT?: Warwick-Edinburgh Mental Well-being Scale (WEMWBS) which is a measurement of mental health and well-being, was translated into Chinese to assess the reliability and validity in a sample of undergraduate nursing trainees in Wenzhou. WHAT THIS PAPER ADDS TO EXISTING KNOWLEDGE?: Currently, there is no a reliable assessment tool to systematically evaluate mental well-being in mainland China. Therefore, we undertook the translation and cultural adaptation of the WEMWBS and tested the scale's reliability and validity. The reliability and validity of the Chinese version of the Short Warwick-Edinburgh Mental Well-being Scale have been demonstrated in Hong Kong, but the WEMWBS has not been validated in mainland China in either clinical or non-clinical settings. WHAT ARE THE IMPLICATIONS FOR PRACTICE?: It might provide a reliable quantitative tool to evaluate mental well-being in non-clinical settings, which has important implications for mental health nursing. In future,it might be a reliable quantitative tool for evaluating mental well-being in other population such as hospitalized patients to improve their life quality.

ABSTRACT

Introduction There is growing interest worldwide in the evaluation of positive mental health and wellbeing. Aim This study was to translate the Warwick-Edinburgh Mental Well-being Scale (WEMWBS) into Chinese and assess the reliability and validity of this scale in a sample of undergraduate nursing trainees. Methods A forward and backward translation protocol was used to translate the scale into Chinese. The psychometric properties of the C-WEMWBS, such as internal consistency reliability, test-retest reliability and factorial validity, were analysed. Results All 14 items of the initial C-WEMWBS were rated as conceptually equivalent to those of the original version. Confirmatory factor analysis indicated the emergence of a single factor. The psychometric properties of the C-WEMWBS were satisfactory, with an internal consistency reliability of .94 and a test-retest reliability of .83. The item-total correlations ranged from .66 to .83. There was a moderate relationship (r = .52) between the C-WEMWBS and the WHO-5. Implications for practice This was the first Chinese version of the WEMWBS to be developed and psychometrically assessed with a sample of undergraduate nursing trainees. It provides a reliable quantitative tool to evaluate mental well-being in non-clinical settings, which has important implications for mental health nursing.

Organizing and managing personal electronic files

This article deals with the organization and management of the computer files handled by mechanical engineers on their personal computers. In engineering organizations, a wide variety of electronic files (documents) are necessary to support both business processes and the activities of design and manufacture. Whilst a large number of files and hence information is formally archived, a significant amount of additional information and knowledge resides in electronic files on personal computers. The widespread use of these personal information stores means that all information is retained. However, its reuse is problematic for all but the individual as a result of the naming and organization of the files. To begin to address this issue, a study of the use and current practices for managing personal electronic files is described. The study considers the fundamental classes of files handled by engineers and analyses the organization of these files across the personal computers of 40 participants. The study involves a questionnaire and an electronic audit. The results of these qualitative and quantitative elements are used to elicit an understanding of the practices and requirements of engineers for managing personal electronic files. A potential scheme for naming and organizing personal electronic files is discussed as one possible way to satisfy these requirements. The aim of the scheme is to balance the personal nature of data storage with the need for personal records to be shared with others to support knowledge reuse in engineering organizations. Although this article is concerned with mechanical engineers, the issues dealt with are relevant to knowledge-based industries and, in particular, teams of knowledge workers.

Oxidative damage in age-related macular degeneration

Epidemiologic studies have suggested that elderly patients who consumed diets rich in antioxidants throughout their lives are less likely to be afflicted with age-related macular degeneration (AMD). This led to the Age-Related Eye Disease Study, which showed that supplements containing antioxidant vitamins and zinc reduce the risk of progression to severe stages of AMD. Despite these data that indirectly implicate oxidative damage in the pathogenesis of AMD, there has not been any direct demonstration of increased oxidative damage in the retinas of patients with AMD. In this study, we used biomarkers of oxidative damage in postmortem eyes from patients with AMD and comparably aged patients without AMD to directly assess for oxidative damage. Sections from 4 eyes with no pathologic features of AMD showed no immunofluorescent staining for markers of oxidative damage, while sections from 8 of 12 eyes with advanced geographic atrophy showed evidence of widespread oxidative damage in both posterior and anterior retina. Only 2 of 8 eyes with choroidal neovascularization and 2 of 16 eyes with diffuse drusen and no other signs of AMD showed evidence of oxidative damage. These data suggest that widespread oxidative damage occurs in the retina of some patients with AMD and is more likely to be seen in patients with advanced geographic atrophy. This does not rule out oxidative damage as a pathogenic mechanism in patients with CNV, but suggests that a subpopulation of patients with geographic atrophy may have a major deficiency in the oxidative defense system that puts the majority of cells in the retina at risk for oxidative damage.

The antitumor activity of TRAIL and IL-24 with replicating oncolytic adenovirus in colorectal cancer

Melanoma differentiation associated gene-7 (Mda-7)/IL-24 was previously cloned into ZD55 (an adenovirus with E1B55 deleted) to form ZD55-IL-24, which had much better antitumor effect than Ad-IL-24. According to its good antitumor properties, ZD55-IL-24 has been used in preclinical studies. But ZD55-IL-24 alone still could not completely eradicate established tumors in all nude mice. It was reported that IL-24 could induce and enhance the activity of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) (a member of tumor necrosis factor (TNF) superfamily). Accordingly, the combined use of ZD55-IL-24 and ZD55-TRAIL was carried out in this study. Treatment with both ZD55-IL-24 and ZD55-TRAIL could induce more significant apoptosis in cancer cells in vitro compared with ZD55-IL-24 or ZD55-TRAIL alone. The combination of the two replicative adenoviruses had better antitumor activity in vivo than that of single oncolytic adenovirus and led to complete eradication of xenograft tumors in all treated mice. Upregulation of TRAIL was observed in tumor cells infected with ZD55-IL-24 and studies of the apoptotic cascade regulators indicate that ZD55-IL-24 could further enhance the activation of apoptosis through the TNF family of death receptors. We demonstrated for the first time the potential therapeutic effect of combined ZD55-IL-24 with ZD55-TRAIL for the targeted therapy of cancer.

Structural and functional analysis of a truncated form of Saccharomyces cerevisiae ATP sulfurylase: C-terminal domain essential for oligomer formation but not for activity

ATP sulfurylase catalyzes the first step in the activation of sulfate by transferring the adenylyl-moiety (AMP approximately ) of ATP to sulfate to form adenosine 5'-phosphosulfate (APS) and pyrophosphate (PP(i)). Subsequently, APS kinase mediates transfer of the gamma-phosphoryl group of ATP to APS to form 3'-phosphoadenosine 5'-phosphosulfate (PAPS) and ADP. The recently determined crystal structure of yeast ATP sulfurylase suggests that its C-terminal domain is structurally quite independent from the other domains, and not essential for catalytic activity. It seems, however, to dictate the oligomerization state of the protein. Here we show that truncation of this domain results in a monomeric enzyme with slightly enhanced catalytic efficiency. Structural alignment of the C-terminal domain indicated that it is extremely similar in its fold to APS kinase although not catalytically competent. While carrying out these structural and functional studies a surface groove was noted. Careful inspection and modeling revealed that the groove is sufficiently deep and wide, as well as properly positioned, to act as a substrate channel between the ATP sulfurylase and APS kinase-like domains of the enzyme.

Structure of human DNMT2, an enigmatic DNA methyltransferase homolog that displays denaturant-resistant binding to DNA

DNMT2 is a human protein that displays strong sequence similarities to DNA (cytosine-5)-methyltransferases (m(5)C MTases) of both prokaryotes and eukaryotes. DNMT2 contains all 10 sequence motifs that are conserved among m(5)C MTases, including the consensus S:-adenosyl-L-methionine-binding motifs and the active site ProCys dipeptide. DNMT2 has close homologs in plants, insects and Schizosaccharomyces pombe, but no related sequence can be found in the genomes of Saccharomyces cerevisiae or Caenorhabditis elegans. The crystal structure of a deletion mutant of DNMT2 complexed with S-adenosyl-L-homocysteine (AdoHcy) has been determined at 1.8 A resolution. The structure of the large domain that contains the sequence motifs involved in catalysis is remarkably similar to that of M.HHAI, a confirmed bacterial m(5)C MTase, and the smaller target recognition domains of DNMT2 and M.HHAI are also closely related in overall structure. The small domain of DNMT2 contains three short helices that are not present in M.HHAI. DNMT2 binds AdoHcy in the same conformation as confirmed m(5)C MTases and, while DNMT2 shares all sequence and structural features with m(5)C MTases, it has failed to demonstrate detectable transmethylase activity. We show here that homologs of DNMT2, which are present in some organisms that are not known to methylate their genomes, contain a specific target-recognizing sequence motif including an invariant CysPheThr tripeptide. DNMT2 binds DNA to form a denaturant-resistant complex in vitro. While the biological function of DNMT2 is not yet known, the strong binding to DNA suggests that DNMT2 may mark specific sequences in the genome by binding to DNA through the specific target-recognizing motif.

Functional roles of the conserved threonine 250 in the target recognition domain of HhaI DNA methyltransferase

DNA cytosine-5-methyltransferase HhaI recognizes the GCGC sequence and flips the inner cytosine out of DNA helix and into the catalytic site for methylation. The 5'-phosphate of the flipped out cytosine is in contact with the conserved Thr-250 from the target recognition domain. We have produced 12 mutants of Thr-250 and examined their methylation potential in vivo. Six active mutants were subjected to detailed biochemical and structural studies. Mutants with similar or smaller side chains (Ser, Cys, and Gly) are very similar to wild-type enzyme in terms of steady-state kinetic parameters k(cat), K(m)(DNA), K(m)(AdoMet). In contrast, the mutants with bulkier side chains (Asn, Asp, and His) show increased K(m) values for both substrates. Fluorescence titrations and stopped-flow kinetic analysis of interactions with duplex oligonucleotides containing 2-aminopurine at the target base position indicate that the T250G mutation leads to a more polar but less solvent-accessible position of the flipped out target base. The x-ray structure of the ternary M. HhaI(T250G).DNA.AdoHcy complex shows that the target cytosine is locked in the catalytic center of enzyme. The space created by the mutation is filled by water molecules and the adjacent DNA backbone atoms dislocate slightly toward the missing side chain. In aggregate, our results suggest that the side chain of Thr-250 is involved in constraining the conformation the DNA backbone and the target base during its rotation into the catalytic site of enzyme.

Cell cycle-dependent proteolysis and ectopic overexpression of cyclin B1 in tobacco BY2 cells

Activation of cyclin B/Cdc2 kinase complex triggers entry into mitosis in all eukaryotic cells. Although cyclin gene expression has been extensively studied in plants, not much is known at the level of the protein stability and function. Here, we demonstrated by using the highly synchronizable tobacco BY2 cell culture, that endogenous cyclin B1 protein undergoes cell cycle-dependent proteolysis and is stabilized when the spindle checkpoint has been activated. Furthermore, we established transgenic tobacco BY2 cell cultures expressing under the control of an inducible promoter, cyclin B1 protein as well as its non-degradable form as fusion proteins with GFP and found that the ectopic expression of these proteins did not dramatically disturb the cell cycle progression. These results indicate that, to a certain extent, cell cycle exit is possible without cyclin B1 proteolysis.

Comparative fourier transform infrared and circular dichroism spectroscopic analysis of alpha1-proteinase inhibitor and ovalbumin in aqueous solution

Alpha1-proteinase inhibitor (alpha1Pi) and ovalbumin are both members of the serpin superfamily. They share about a 30% sequence identity and exhibit great similarity in their three-dimensional structures. However, no apparent functional relationship has been found between the two proteins. Unlike alpha1Pi, ovalbumin shows no inhibitory effect to serine proteases. To see whether or not a conformational factor(s) may contribute to the functional difference, we carried out comparative analysis of the two proteins' secondary structure, thermal stability, and H-D exchange using FT-IR and CD spectroscopy. FT-IR analysis reveals significant differences in the amide I spectral patterns of the two proteins. Upon thermal denaturation, both proteins exhibit a strong low-wavenumber beta-sheet band at 1624 cm(-1) and a weak high-wavenumber beta-sheet band at 1694 cm(-1), indicative of intermolecular aggregate formation. However, the midpoint of the thermal-induced transition of alpha1Pi (approximately 55 degrees C) is 18 degrees C lower than that of ovalbumin (approximately 73 degrees C). The thermal stability analysis provides new insight into the structural changes associated with denaturation. The result of H-D exchange explains some puzzling spectral differences between the two proteins in D2O reported previously.

Entrapping intermediates of thermal aggregation in alpha-helical proteins with low concentration of guanidine hydrochloride

Aggregation of proteins is a problem with serious medical implications and economic importance. To develop strategies for preventing aggregation, the mechanism(s) and pathways by which proteins aggregate must be characterized. In this study, the thermally induced aggregation processes of three alpha-helix proteins (myoglobin, cytochrome c, and lysozyme) in the presence and absence of 1.0 m guanidine hydrochloride (GdnHCl) were investigated by means of infrared spectroscopy. In the absence of GdnHCl, intensities of the alpha-helix bands (approximately 1656 cm(-1)) decrease as a function of temperature at above 50 degrees C. With myoglobin and cytochrome c, the loss of helix bands was accompanied by the appearance of two new bands at 1694 and 1623 cm(-1), indicative of the formation of intermolecular beta-sheet aggregates. For lysozyme, bands indicative of intermolecular beta-sheet aggregates did not appear in any significant intensity. In the presence of 1.0 m GdnHCl, two major intermediate states rich in 3(10)-helix (represented by the band at 1663 cm(-1)) and beta-turn structure (represented by the band at 1667 cm(-1)), respectively, were observed. These findings demonstrated that IR spectroscopic studies of protein aggregation using a combination of thermal and chemical denaturing factors could provide a means to populate and characterize aggregation intermediates.

Antifungal, antimitotic and anti-HIV-1 agents from the roots of Wikstroemia indica

With guidance of Pyricularia oryzae bioassay, daphnoretin (1), (+)-nortrachelogenin (2), genkwanol A (3), wikstrol A (4), wikstrol B (5) and daphnodorin B (6) were isolated from the roots of Wikstroemia indica. Compounds 1-6 induced morphological deformation of P. oryzae mycelia with MMDC values of 68.4 +/- 1.3, 31.3 +/- 1.8, 45.8 +/- 0.5, 70.1 +/- 2.4, 52.3 +/- 0.9 and 73.7 +/- 1.6 microM, respectively. Compounds 3-6 showed moderate activity against microtubule polymerization with IC50 values of 112 +/- 4, 131 +/- 3, 184 +/- 6 and 142 +/- 2 microM in vitro, respectively. Compounds 2, 3, 5 and 6 were moderately active against HIV-1 in vitro. The findings of bioactivity of 1-6 support the antifungus, antimitosis and anti-HIV-1 uses for W. indica roots.

A novel calmodulin-like protein gene in rice which has an unusual prolonged C-terminal sequence carrying a putative prenylation site

A rice cDNA encoding a novel calmodulin-like protein was identified. It has 38 additional amino acids at the C-terminus of a complete, typical calmodulin (CaM) sequence of 149 amino acids. The four C-terminal amino acid residues form a CAAL motif which could be a site for protein prenylation and may subsequently cause the protein to become membrane associated. RT-PCR analysis confirmed that such a combined protein gene truly exists in rice. Sequence analysis of its genomic counterpart showed that there is an intron located at junction of the normal CaM sequence and the 38 C-terminal amino acids. This introduces a potential stop codon for normal CaM if an alternative splicing mechanism is involved. Southern blot analysis of rice genomic DNA revealed that there is only one locus for this gene. The northern blot analysis showed that this gene is highly expressed in rice roots, shoots and flowers. The distribution of this protein demonstrates the functional importance of this novel CaM-like protein in rice.

Preparation and Morphology Studies of Core-Shell Type Waterborne Polyacrylate-Polyurethane Microspheres

Core-shell type waterborne polyacrylate-polyurethane microspheres in which polyurethane acts as the shell and acrylic polymer as the core were prepared. Hydroxyethyl acrylate and adipic dihydrazide were used as cross-linking agents introduced to the ends of the shell molecular chains, and two kinds of cross-linked structures between the core and the shell were formed. The photon correlation spectroscopy studies indicate that all the microspheres present continuous particle-size distributions and their mean particle sizes are smaller than 200 nm. The transmission electron photographs reveal that there are obvious core-shell structures for the noncross-linked type microsphere particles and different cross-linked networks between the core and shell for the two kinds of cross-linked type microsphere particles. These microspheres possess excellent storage stability, water resistance, and coating properties. Copyright 1999 Academic Press.

Antineoplastic agents. III: Steroidal glycosides from Solanum nigrum

By bioactivity-guided fractionation, three known steroidal glycosides, beta 2-solamargine (1), solamargine (2), and degalactotigonin (3), were isolated from Solanum nigrum. Compounds 1-3 induced morphological abnormality in Pyricularia oryzae mycelia with MMDC (minimum morphological deformation concentration) values of 63.0, 38.5, and 97.2 microM, respectively. This is the first report on the isolation of 1 from this species and on the cytotoxicity of 1-3 on six cultured human solid tumor cell lines HT-29 (colon), HCT-15 (colon), LNCaP (prostate), PC-3 (prostate), T47D (breast), and MDA-MB-231 (breast) in vitro. The cytotoxic assay indicated that 2 is the main antineoplastic agent in S. nigrum. The structures of 1-3 were elucidated on the basis of chemical evidence and spectral analysis, especially by 2D-NMR analysis.

Use of infrared spectroscopy to assess secondary structure of human growth hormone within biodegradable microspheres

The purpose of this study was to test the utility of infrared (IR) spectroscopy to determine protein secondary structure in biodegradable microspheres. Encapsulation of proteins within biodegradable polymers, [e.g. poly(lactic-co-glycolic acid) (PLGA)] for controlled drug release has recently been the subject of intense research effort. The ability to assess protein integrity after microsphere production is necessary to successfully produce microspheres that release native proteins. We used IR spectroscopy, a noninvasive method-as opposed to conventional organic solvent extraction or in vitro release at elevated temperature-to assess the secondary structure of recombinant human growth hormone (rhGH) within dry and rehydrated microspheres. PLGA microspheres containing rhGH with different excipients were prepared by a conventional double-emulsion method. The protein IR spectra indicated that the encapsulation process could perturb the structure of rhGH and that excipients could inhibit this damage to varying degrees. A strong positive correlation was found between intensity of the dominant alpha-helical band in the spectra of rhGH in rehydrated microspheres and the percent monomer released from microspheres during incubation in buffer. We also studied microspheres prepared with zinc-precipitated rhGH. The addition of Zn2+ during microsphere processing partially inhibited protein unfolding and fostered complete refolding of rhGH upon rehydration. In conclusion, IR spectroscopy can serve as a valuable tool to assess protein structure within both dried and rehydrated microspheres.

The magnitude of changes in guanidine-HCl unfolding m-values in the protein, iso-1-cytochrome c, depends upon the substructure containing the mutation

Hydrophilic to hydrophobic mutations have been made at 11 solvent exposed sites on the surface of iso-1-cytochrome c. Most of these mutations involve the replacement of lysine with methionine, which is nearly isosteric with lysine. Minimal perturbation to the native structure is expected, and this expectation is confirmed by infrared amide I spectroscopy. Guanidine hydrochloride denaturation studies demonstrate that these variants affect the magnitude of the m-value, the rate of change of free energy with respect to denaturant concentration, to different degrees. Changes in m-values are indicative of changes in the equilibrium folding mechanism of a protein. Decreases in m-values are normally thought to result either from an increased population of intermediates during unfolding or from a more compact denatured state. When cytochrome c is considered in terms of its thermodynamic substructures, the changes in the m-value for a given variant appear to depend upon the substructure in which the mutation is made. These data indicate that the relative stabilities and physical properties of substructures of cytochrome c play an important determining role in the equilibrium folding mechanism of this protein.

Intermolecular beta-sheet results from trifluoroethanol-induced nonnative alpha-helical structure in beta-sheet predominant proteins: infrared and circular dichroism spectroscopic study

2,2,2-Trifluoroethanol (TFE)-induced nonnative alpha-helical structure in peptides and proteins has been extensively studied with circular dichroism (CD) spectroscopy. However, to date, complementary information from infrared (IR) spectroscopy has not been reported. Using both IR and CD spectroscopy, we demonstrate here that the TFE-induced nonnative alpha-helical structure in two beta-sheet-predominant proteins, beta-lactoglobulin and alpha-chymotrypsin, is unstable in comparison with those found in the alpha-helix-predominant proteins myoglobin and cytochrome c under identical conditions. IR spectra showed that, immediately after dissolution of the beta-sheet proteins in 50% (v/v) TFE, a strong amide I band component appears at 1654 cm-1 in H2O and at 1650 cm-1 in D2O, which is ascribed to alpha-helical structure. However, the intensities of the alpha-helical bands decrease as a function of time, concomitant with the appearance of two new band components near 1620 and 1695 cm-1 in H2O and 1612 and 1684 cm-1 in D2O, a typical IR spectral pattern for an intermolecular beta-sheet aggregate. Clear gels begin to develop within 30 min. No similar spectral changes were observed for the alpha-helical proteins. CD spectra suggested initially that the TFE-induced alpha-helix was retained in the gelled state. However, further analysis of the spectra, and Gaussian function modeling with basic spectra, indicated that the apparent alpha-helix signal was actually due to a combination of signals from intermolecular beta-sheet and residual alpha-helix. These results indicate that the TFE-induced nonnative alpha-helix structure in predominantly beta-sheet proteins is unstable and readily converts to an intermolecular beta-sheet aggregate.

Spectroscopic study of secondary structure and thermal denaturation of recombinant human factor XIII in aqueous solution

The secondary structure and thermal denaturation (in H2O vs D2O) of recombinant human factor XIII in aqueous solutions were investigated using infrared and circular dichroism (CD) spectroscopies. The infrared amide I spectrum of the protein in H2O solution at 25 degrees C exhibited an absorbance maximum near 1642 cm-1, indicating the presence of a predominantly beta-sheet structure. Quantitative analysis revealed that the native protein contains 13-16% alpha-helix, 41-49% beta-sheet, 29% beta-turn, and 10-14% extended strand structures. The presence of a strong low-wavenumber beta-sheet band at 1641 cm-1 and a weak high-wavenumber beta-sheet band at 1689 cm-1 indicated that the beta-sheet structure of the protein is predominantly antiparallel. Quantitative analysis of the CD spectrum using the SELCON method indicated a secondary structural content of 10% alpha-helix, 40-50% beta-sheet, 20-35% beta-turns, and 20-35% unordered elements, which matches that determined by X-ray crystallography. The apparent discrepancy with the contents of unordered element determined by infrared spectroscopy is reconciled by considering that CD spectroscopy and X-ray crystallography assign extended loops and strands to unordered elements, whereas infrared spectroscopy recognizes these as distinct structured elements. During heating above 60 degrees C, a pair of new infrared bands appeared at 1626 and 1693 cm-1 for the protein in H2O and 1619 and 1683 cm-1 in D2O, indicating a formation of intermolecular beta-sheet aggregates. The intensities of the new bands increased as a function of temperature, concomitant with an intensity decrease in bands for the native protein structural elements. As expected, there was an increase in thermal stability in D2O relative to that in H2O, which was manifested as an increase of about 5 degrees C in the temperature for initial loss of infrared bands assigned to native structural elements and for appearance of bands due to intermolecular beta-sheet. In addition, the midpoint of the thermally induced transitions in infrared spectra were about 2.5 degrees C higher in D2O than in H2O. Based on the infrared analysis, the thermally denatured state of the protein in both H2O and D2O contains predominantly intermolecular beta-sheet. The broad, poorly resolved absorbance that spans the region between the intermolecular beta-sheet bands was assigned to an ensemble of heterogeneous structural elements (including unordered), none of which is populated to a high enough degree to result in a distinct infrared band. Results from CD spectroscopy support these conclusions about the structure of the denatured, aggregated protein.

Redox-dependent conformational changes are common structural features of cytochrome c from various species

Discrepant results from X-ray crystallographic and physicochemical studies on the conformations of the two redox states of cytochrome c raise important questions about the nature of redox-dependent conformational changes and whether differences are common structural features of various cytochrome c species. Comparative studies of cytochrome c from 10 species (horse, cow, sheep, pig, dog, rabbit, chicken, pigeon, tuna, and baker's yeast) in aqueous solutions were carried out using Fourier transform infrared (FT-IR) spectroscopy. The second-derivative analysis revealed similar conformational changes in all 10 species upon reduction of the heme iron regardless of the differences in the amino acid sequences. The redox-dependent changes involve the amide I regions ascribed to extended beta-structure, beta-turn, and alpha-helix structures. Three species (cow, sheep, and pig) with identical amino acid sequences displayed nearly identical infrared spectra for the oxidized and reduced states, which rules out the possible contribution of experimental error. These results show unequivocally that redox-dependent conformational changes are common structural feature of various cytochrome c species and demonstrate the usefulness of FT-IR spectroscopy as a quick and inexpensive tool in comparative studies of functionally related conformational changes of proteins.

Drug delivery matrix containing native protein precipitates suspended in a poloxamer gel

Sustained delivery systems can achieve more constant blood levels of protein therapeutics than those obtained with bolus doses, leading to improved drug efficacy and fewer adverse side effects. Several different polymeric delivery systems have been studied, including poloxamers, which are unique because they can be prepared in aqueous buffers that are compatible with proteins. Poloxamers are nontoxic block copolymers of poly(ethylene oxide) and poly(propylene oxide). Certain poloxamers exhibit reversible thermal gelation. Thus, a solution of protein and poloxamer prepared at low temperatures and injected extravascularly will form a gel as it warms to body temperature. Subsequently, the protein is released slowly from the gel. To date, however, poloxamer gel delivery systems have been limited to relatively low protein concentrations (i.e., < or = 0.4 mg/mL) that produce a completely soluble protein and an optically clear gel. Much higher concentrations of other protein drugs might be needed to obtain an efficacious sustained dose. In the current in vitro study we found that a poloxamer 407 (22% wt/wt) matrix could be prepared containing tens of milligrams/mililiter of the model proteins alpha-chymotrypsin and lactate dehydrogenase. Under these conditions the protein forms a homogeneous suspension. Warming through the poloxamer 407 transition temperature (ca. 18 degrees C) results in a gel that retains a homogeneous distribution of protein precipitates for several days at 37 degrees C. Infrared spectroscopy documented that the precipitated proteins in the suspension have native secondary structure. Furthermore, the fully active protein can be recovered completely when the gel is dissolved in excess buffer. Finally, at the higher protein concentrations used to form the suspensions in poloxamer 407, protein stability during incubation at 37 degrees C was greatly improved over that seen at lower protein concentrations.

Secondary structure of recombinant human cystathionine beta-synthase in aqueous solution: effect of ligand binding and proteolytic truncation

The secondary structural composition and substrate-induced conformational changes of recombinant human cystathionine beta-synthase (CBS) in aqueous solution have been investigated in its full-length form (tetramer of 63-kDa subunits) by Fourier transform infrared (FT-IR) and circular dichroism (CD) spectroscopies. In addition, structural comparison of a proteolytic truncated form (dimer of 45-kDa subunits) to that of the full-length enzyme has also been carried out. Second-derivative and Fourier self-deconvolutional enhanced infrared spectra revealed amide I band components ascribed to beta-sheet (1689, 1638, and 1627 cm(-1)), alpha-helix (1658 cm(-1)), beta-turn (1679 and 1668 cm(-1)), and unordered (1651 cm(-1)) structures in the spectra of the full-length enzyme. Quantitative analysis of FT-IR and CD spectra reveals that the full-length enzyme consists of about 48-53% beta-sheet, 25-30% alpha-helix, 8-10% turn, and 10-19% unordered structures. Under constraint of the spectroscopic data, theoretical prediction of locations of these secondary structural elements using Garnier's method shows that human CBS may contain a beta-sheet/alpha-helix/beta-sheet core structure. Second-derivative spectrum of the truncated enzyme exhibited all the major spectral features that are present in the full-length enzyme, indicating a preservation of the core structure of the enzyme. Significant differences were observed between the infrared spectra of the enzymes with or without the substrate, serine, indicating a substrate-induced conformational change in the enzyme, which did not result in a change in overall composition of secondary structural content based on quantitative analysis of FT-IR and far-UV CD spectra.

Antineoplastic agents. II. Four furostanol glycosides from rhizomes of Dioscorea collettii var. hypoglauca

During activity-guided fractionations to screen for antineoplastic agents, further studies by means of preparative HPLC led to the isolation of four known furostanol saponins: protoneodioscin, protodioscin, protoneogracillin, protogracillin, along with their corresponding artifacts: methyl protoneodioscin, methyl protodioscin, methyl protoneogracillin, and methyl protogracillin, from the rhizomes of Dioscorea collettii var. hypoglauca. Among them, protoneodioscin, protodioscin, and protoneogracillin are first reported from the title plant. The structures of the compounds were established on the basis of chemical evidence and spectral analysis (1H-NMR, 13C-IMMR, 1H-1H COSY, HMQC, HMBC, and FAB-MS). These eight compounds all caused morphological abnormality of Pyricularia oryzae mycelia. They also showed cytotoxic activities against the cancer cell line of K562 in vitro as antineoplastic agents.

A lysine 73-->histidine variant of yeast iso-1-cytochrome c: evidence for a native-like intermediate in the unfolding pathway and implications for m value effects

In this paper we report thermodynamic studies on a variant of yeast iso-1-cytochrome c in which a surface lysine residue at position 73 has been replaced with a histidine (H73). Guanidine hydrochloride denaturation studies monitored by circular dichroism spectroscopy indicated decreased thermodynamic stability (a lower delta G(o)(u)H20) and a smaller m value for the H73 protein as compared to the wild type (WT) protein. Further investigations to probe the causes for the thermodynamic stability differences between the two proteins involved guanidine hydrochloride and urea denaturations monitored by tryptophan fluorescence. The stability of heme ligation in the denatured state in the presence of either guanidine hydrochloride or urea was monitored by the spin-state transition of the heme iron induced by pH. None of these studies supported the hypothesis that the decreased m value was due to heme-His73 ligation in the denatured state. Guanidine hydrochloride denaturations monitored by the change in the extinction coefficient at 695 nm, which is sensitive to the presence of heme-Met80 ligation, revealed a native-like intermediate for the H73 protein, probably caused by displacement of the Met80 heme ligand by histidine 73 at guanidine hydrochloride concentrations much lower than required for full cooperative unfolding. Presence of the native-like intermediate is most likely the cause of the smaller m value and decreased thermodynamic stability for the CD-monitored H73 protein unfolding as compared to the unfolding of the WT protein. Guanidine hydrochloride denaturations in the presence of 200 mM imidazole provide further evidence in support of the proposed mechanism.

Antineoplastic agents; I. Three spirostanol glycosides from rhizomes of Dioscorea collettii var. hypoglauca

By activity-guided fractionation, three known steroidal saponins, prosapogenin A of dioscin, dioscin and gracillin, were isolated from the total saponin fraction of Dioscorea coiletti var. hypoglauca as active compounds causing morphological abnormality of Pyricularia oryzae mycelia. The compounds also exhibited cytotoxic activity against the cancer cell line K562 in vitro. The structures of the compounds were elucidated on the basis of chemical evidence and IR, FAB-MS, 1H-NMR, 13C-NMR, and two-dimensional NMR (2D-NMR) analysis.

Formation of an active dimer during storage of interleukin-1 receptor antagonist in aqueous solution

The degradation products of recombinant human interleukin-1 receptor antagonist (rhIL-1ra) formed during storage at 30 degrees C in aqueous solution were characterized. Cationic exchange chromatography of the stored sample showed two major, new peaks eluting before (P1) and after (L2) the native protein, which were interconvertible. Size-exclusion chromatography and electrophoresis documented that both the P1 and L2 fractions were irreversible dimers, formed by noncovalent interactions. A competition assay with interleukin-1 indicated that on a per monomer basis the P1 and L2 dimers retained about two-thirds of the activity of the native monomer. Infrared and far-UV circular dichroism spectroscopies showed that only minor alterations in secondary structure arose upon the formation of the P1 dimer. However, alteration in the near-UV circular dichroism spectrum suggested the presence of disulfide bonds in the P1 dimer, which are absent in the native protein. Mass spectroscopy and tryptic mapping, before and after carboxymethylation, demonstrated that the P1 dimer contained an intramolecular disulfide bond between Cys-66 and Cys-69. Although conversion of native protein to the P1 dimer was irreversible in buffer alone, the native monomer could be regained by denaturing the P1 dimer with guanidine hydrochloride and renaturing it by dialysis, suggesting that the intramolecular disulfide bond does not interfere with refolding. Analysis of the time course of P1 formation during storage at 30 degrees C indicated that the process followed first-order, and not second-order, kinetics, suggesting that the rate-limiting step was not dimerization. It is proposed that a conformational change in the monomer is the rate-limiting step in the formation of the P1 dimer degradation product. Sucrose stabilized the native monomer against this process. This result can be explained by the general stabilization mechanism for this additive, which is due to its preferential exclusion from the protein surface.

Effect of secondary structure on the activity of enzymes suspended in organic solvents

Despite the extensive use and study of enzymes suspended in organic solvents, whether activity differences between different preparations can be accounted for by differences in protein secondary structure is still unknown. To address this issue, in the current study two model enzymes, alpha-chymotrypsin and subtilisin Carlsberg, were lyophilized and suspended in both polar and nonpolar organic solvents. The secondary structures of the proteins in the initial aqueous solution, in the lyophilized powder, and in the subsequent suspensions in organic solvents were determined using infrared spectroscopy. Lyophilization perturbed the secondary structure of both enzymes. With alpha-chymotrypsin, lyophilization from buffer followed by suspension in ethanol, hexane, or pyridine did not alter the unfolded structure observed in the dried powder. In contrast, with subtilisin Carlsberg, suspension of the dried enzyme in ethanol led to further perturbation of structure, whereas in hexane, and more so in pyridine, there was some return toward native structure. Lyophilization of the aqueous protein solutions in the presence of either trehalose or sorbitol led to retention of more native-like structure of both enzymes in the dried solid. However, large structural perturbations arose when these samples were suspended in organic solvents. The only exception was the subtilisin-trehalose mixture, which regained some native structure in ethanol and hexane. The greatest changes were noted in samples suspended in pyridine, in which the infrared spectra indicated extensive intermolecular beta-sheet formation from protein aggregates. There was not any consistent correlation between activity in organic solvents and either the initial structure obtained in the dried powders or the final structure when suspended in organic solvents. Nor could differences in residual water contents in dried samples or the total water content in the organic solvent reaction system account for the activity differences.

Counteracting effects of thiocyanate and sucrose on chymotrypsinogen secondary structure and aggregation during freezing, drying, and rehydration

Studies of numerous proteins with infrared spectroscopy have documented that unfolding is a general response of unprotected proteins to freeze-drying. Some proteins that are unfolded in the dried solid aggregate during rehydration, whereas others refold. It has been proposed for the latter case that aggregation is avoided because refolding kinetically outcompetes intermolecular interactions. In contrast, with proteins that normally aggregate after rehydration, minimizing unfolding during freeze-drying with stabilizer has been shown to be needed to favor the recovery of native protein molecules after rehydration. The purpose of the current study was to examine first the opposite situation, in which a denaturant is used to foster additional unfolding in the protein population during freeze-drying. If the protein is not intrinsically resistant to aggregation under the study conditions (e.g., because of intermolecular charge repulsion) and the denaturant does not disrupt intermolecular interactions during rehydration, this treatment should favor aggregation upon rehydration. With infrared spectroscopy we found that at concentrations of the denaturant Na thiocyanate (NaSCN) that only slightly perturbed chymotrypsinogen secondary structure in solution before freeze-drying, there was a large increase in protein unfolding in the dried solid and in protein aggregation measured after rehydration. Bands assigned to intermolecular beta sheet were present in the spectra of samples dried with NaSCN, indicating that aggregation could also arise in the dried solid. By examining the protein structure in the frozen state, we determined that in the absence of NaSCN the protein remains native. NaSCN caused structural perturbations during freezing, without the formation of intermolecular beta sheet, that were intermediate to structural changes noted after freeze-drying. In contrast, samples treated in the presence of NaSCN and sucrose had native-like spectra in the frozen and dried states, and much reduced aggregation after rehydration. These results indicate that during freezing and drying the sugar can counteract and mostly reverse the structural perturbations induced by NaSCN before and during these treatments.

Differences in conformational dynamics of ribonucleases A and S as observed by infrared spectroscopy and hydrogen-deuterium exchange

Differences in conformational dynamics of bovine pancreatic RNase A and RNase S have been investigated using hydrogen-deuterium (H-D) exchange in conjunction with Fourier transform infrared spectroscopy. Deuteration-induced spectral changes in the amide I and II regions were monitored as a function of time. Second-derivative analysis revealed similar amide I spectral patterns for both proteins in H2O as well as fully deuterated in D2O. However, the rate of amide proton exchange of RNase S is much faster than that of RNase A at 25 degrees C as determined by changes in the intensity ratio of amide II/amide I bands and frequency red-shifts of amide I components. The frequency red-shifts of the amide I components ascribed to beta-sheet, alpha-helix, and beta-turns are continuous as a function of time, indicating that both proteins are too small to contain isolated secondary structural groups containing only exchanged or unexchanged amide protons in the partially deuterated intermediate states. Despite the dramatic difference in H-D exchange rate, the patterns of spectral changes in the conformation-sensitive amide I regions of RNase A and RNase S are very similar throughout the course of deuteration, indicating a similar pathway of amide proton exchange in both proteins.