Understanding the effects of chitosan, chia mucilage, levan based composite coatings on the shelf life of sweet cherry

Sweet cherry (Prunus avium L.) fruits are prone to quality and quantity loss in shelf-life conditions and cold storage due to their short post-harvest life. Until now efforts have been made to extend the shelf life of the sweet cherry. However, an efficient and commercially scalable process remains elusive. To contribute to this challenge, here in this study, biobased composite coatings consisting of chitosan, mucilage, and levan, were applied on sweet cherry fruits and tested for postharvest parameters in both market and cold storage conditions. Results demonstrated that the shelf life of sweet cherries can be extended until the 30^th day while retaining important post-harvest properties like decreased weight loss, fungal deterioration, increased stem removal force, total flavonoid, l-ascorbic acid, and oxalic acid. Given the cost-effectiveness of the polymers used, the findings of this study indicate the feasibility of extending the shelf-life of sweet cherries on a larger scale.

Effect of aquaporin 1 and 4 on masticatory muscles degeneration as a result of aging

OBJECTIVE

The changes in the mouth structures due to aging cause some structural and functional changes by affecting masticatory muscles over time. The aim of this study was to evaluate the aging-related histopathologic changes and immunohistochemically assessed aquaporin 1 and 4 expressions on masseter and temporal muscles.

MATERIAL AND METHODS

14 Balb/c white mice (50-80 g) were used in this study. Group I consisted of young animals (2-month-individuals) (n = 7) and Group II consisted of older animals (18-month-old) (n = 7). After routine histological follow-ups were made, tissues were stained immunohistochemically for aquaporin 1 and aquaporin 4 as well as with hematoxylin-eosin.

RESULTS

It was seen that while the masseter and temporalis muscle tissues showed a high immunoreactivity (+++) for aquaporin 1 and 4 in young mice, they showed a weak immunoreactivity (+) for aquaporin 1 and 4 in old mice (p = 0.001). In the H-score assessment, aquaporin 1 and 4 immunoreactivity was significantly higher in young mice than in old mice (p = 0.002).

CONCLUSIONS

Consequently, it was shown that degeneration of the masticatory muscles increased with aging and there was a decrease in intra- and intercellular exchange of substances because of changing aquaporin 1 and aquaporin 4 expressions (Tab. 2, Fig. 4, Ref. 20).

P3-16-09: Endoxifen, a Newly Developed Breast Cancer Drug, Has Anabolic Actions on the Mouse Skeleton

Background

Commonly used endocrine therapies for breast cancer, such as aromatase inhibitors in postmenopausal women and tamoxifen in premenopausal women, have deleterious effects on bone mineral density. Therefore, the identification of novel cancer therapies which either maintain or improve bone mass are of clinical need. We have recently demonstrated that endoxifen is the most active tamoxifen metabolite with regard to inhibiting the growth of ERα+ breast cancer cells and these studies have led to the development of endoxifen as a novel anti-breast cancer drug for which first-in-human studies are now underway. At present, there are no data regarding endoxifen's effects on bone.

Methods: The effects of endoxifen on osteoblast (OB) and osteoclast (OC) maturation and gene expression were monitored by cell differentiation assays and real-time PCR. Dual-energy X-ray absorptiometry (DXA), peripheral Quantitative Computed Tomography (pQCT) and micro-Computed Tomography (μCT) were used to determine changes in bone density, mass and architecture following 45 days of oral endoxifen administration (50mg/kg/day) to 3-month-old ovariectomized (OVX) C57BL/6 mice relative to vehicle control treated animals. Alterations in the numbers and activity of OBs and OCs were determined by histomorphometry and serum levels of P1NP and CTX-1 respectively.

Results: Endoxifen treatment of mouse derived bone marrow stromal cells and human OBs led to significant increases in the expression of critical bone marker genes such as Runx2, osterix, osteocalcin, osteoprotegerin and alkaline phosphatase in a dose dependent manner. Daily administration of endoxifen to OVX mice led to significant increases in total body bone mineral density (BMD) (6%) and content (BMC) (9%), which was accompanied by a 50% decrease in fat tissue mass as determined by DXA. pQCT analysis of the tibial metaphysis revealed dramatic increases in BMD (35%) and BMC (20%), as well as trabecular density (52%), cortical content (62%), cortical area (60%) and cortical thickness (78%). μCT analysis of the femoral metaphysis revealed increases in bone volume/total volume (200%), trabecular number (38%) and trabecular thickness (18%), as well as decreased trabecular spacing (29%). Interestingly, there was nearly a 50% increase in the numbers of OCs derived from endoxifen treated mice which was associated with elevated expression of OC marker genes such as NFATcl, RANK, c-fms and cathepsin-K compared to control treated animals. Approximately 4 times as many OBs and OCs were observed on the bone surfaces of endoxifen treated mice which correlated with nearly 2-fold increases in serum levels of the bone formation (P1NP) and resorption (CTX-1) markers.

Conclusions: These data are the first to demonstrate that endoxifen has anabolic effects on the mouse skeleton which are similar to that of estrogen. Additionally, these data reveal that endoxifen's mechanism of action in bone is different than that reported for tamoxifen and other selective estrogen receptor modulators in mice as it increases, rather than decreases, bone formation and remodeling. Therefore, the use of endoxifen for the treatment of endocrine responsive breast cancer may avoid the detrimental skeletal effects of many conventional endocrine therapies.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-16-09.

P4-02-03: Biological Functions of Estrogen Receptor-beta and Its Variants in Breast Cancer

Background

The role of estrogen receptor alpha (ERα) in breast cancer has been studied extensively; yet, much less is known about full-length ERβ (ERβ1) and even less about its 4 variant forms (ERβ2-5). We have recently implicated a role for ERβ1 in sensitizing ERα expressing breast cancer cells to anti-estrogens. However, the ability of ERβ2-5 to modulate ERα and ERβ1 activity, and their association with cancer development, progression, and response to estradiol (E2) and anti-estrogens are not well understood. Here, we provide evidence that the presence of ERβ variants may be of diagnostic and clinical relevance for breast cancer patients and describe the development and characterization of a novel, highly specific monoclonal antibody (MC10) that is able to detect their expression in tumor biopsies.

Methods: Transient transfection and luciferase assays were used to determine the transcriptional activity of ERβ2-5 in response to E2 and anti-estrogens alone or in combination with ERα and ERβ1. A novel monoclonal antibody targeting all ERβ variants (MC10) was developed and characterized. The sub-cellular localization of ERβ2-5 was determined via confocal microscopy. Finally, the MC10 antibody was used to assess ERβ positivity in breast tumors and was compared to that of another monoclonal antibody which only detects ERβ1.

Results: Unlike ERβ1, ERβ2-5 do not activate an estrogen response element (ERE) in response to E2 and instead, slightly repress the activity of this reporter construct. Expression of ERβ2-5 does not significantly alter the transcriptional activity of ERβ1 following E2 treatment. However, ERβ2, 3 and 5, but not ERβ4, significantly enhance the E2-induced transcriptional activity of ERα. Interestingly, expression of ERβ3, 4 and 5, but not ERβ2, enhance the ability of anti-estrogens to block ERα mediated transcriptional activity. Confocal microscopy revealed that ERβ1 and 2 are almost exclusively localized to the cell nucleus. However, ERβ3-5 exhibit significant cytoplasmic and peri-nuclear localization. Immunohistochemistry of breast cancer biopsies using the MC10 antibody revealed multiple staining patterns including tumors which exhibit primarily nuclear staining and others primarily cytoplasmic, both in the presence and absence of ERα. These results are in contrast to the almost exclusive nuclear staining obtained on the same tumors with an ERβ1-specific antibody.

Conclusions: ERβ variants exhibit variable sub-cellular localization patterns and can influence the function of ERα, both in response to E2 and anti-estrogens. Therefore, the differential expression of ERβ variants and their cellular localization may influence breast cancer progression and/or therapeutic responses. The use of ERβ antibodies which do not detect all ERβ variants, or the use of a single ERβ antibody which does not discriminate between ERβ1 and its variants, is unlikely to reveal the complete biological significance of total ERβ expression in breast cancer and may in part explain the conflicting studies which have been reported for ERβ in the field.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-02-03.

TGFbeta inducible early gene-1 directly binds to, and represses, the OPG promoter in osteoblasts

TGFbeta inducible early gene-1 (TIEG) is a member of the Krüppel-like family of transcription factors (KLF10) that plays an important role in TGFbeta mediated Smad signaling. In order to better understand the role of TIEG in bone, we generated TIEG knockout (KO) mice. Calvarial osteoblasts (OBs) isolated from these mice exhibit a reduced ability to support osteoclastogenesis in vitro. Gene expression studies revealed decreased receptor activator of NF-kappaB ligand (RANKL) and increased osteoprotegerin (OPG) expression in TIEG KO OBs, suggesting a potential role for TIEG in regulating the expression of these genes. Since OPG and RANKL are two important regulators of osteoclast (OC) differentiation, we sought to determine if TIEG directly regulates their expression. Luciferase constructs, containing fragments of either the mouse OPG promoter (-1486 to +133 bp) or the RANKL promoter (-2000 to +1 bp) were each cloned into the pGL3 basic reporter vector and transiently transfected into TIEG KO calvarial OBs with and without a TIEG expression vector. No significant changes in the activity of the RANKL promoter were detected in the presence of TIEG. However, OPG promoter activity was inhibited in the presence of TIEG protein suggesting that TIEG directly represses the expression of OPG in OBs. In order to determine the region of this promoter through which TIEG acts, sequential 5'-deletion constructs were generated. Transient transfection of these constructs revealed that the TIEG regulatory element(s) reside within a 200 bp region of the OPG promoter. Transient ChIP analyses, using a TIEG-specific antibody, revealed that TIEG binds to this region of the OPG promoter. Since we have previously shown that TIEG regulates target gene expression through Sp-1 sites, we examined this region of the OPG promoter for potential TIEG binding elements and identified four potential Sp-1 binding sites. Site-directed mutagenesis was used to determine if TIEG utilizes these Sp-1 elements to regulate the activity of the OPG promoter. The data demonstrate that two Sp-1 sites are likely to be involved in TIEG's repression of the OPG promoter. Taken together, these results confirm that TIEG directly binds to and inhibits OPG promoter activity in OBs, partially explaining the inability of TIEG KO OBs to fully support osteoclast differentiation.

Seasonal changes of metal accumulation and distribution in common club rush (Schoenoplectus lacustris) and common reed (Phragmites australis)

In this study, two aquatic macrophytes Phragmites australis and Schoenoplectus lacustris and corresponding sediment samples were collected every three months from Lake Sapanca (Turkey) and analysed for their heavy-metal contents (Pb, Cr, Cu, Mn, Ni, Zn and Cd). Accumulation factor ratios of plant parts were calculated for all metals, and the two species were compared in terms of accumulation properties. The highest concentrations were measured in the root systems while relatively low concentrations were found in the rhizome and above-ground parts of the plants. The accumulation ratios of root for P. australis were usually higher than the ratios for S. lacustris. While the accumulation ratios of root were higher in winter than in the other seasons for P. australis, for S. lacustris the highest accumulation ratios were found in the autumn. Both plant species were found to be root accumulators of Pb, Cu, Mn, Ni, Zn and Cd.

Dexpanthenol pastille and benzydamine hydrochloride spray for the prevention of post-operative sore throat

BACKGROUND

In this study, we aimed to compare the effectiveness of dexpanthenol pastille and benzydamine hydrochloride spray on the prevention of a sore throat.

METHODS

One hundred and eighty patients undergoing general anaesthesia, who were ASA I-II and with their ages ranging between 15 and 70 years, were randomly allocated to three groups, each consisting of 60 patients. For group B, four puffs of benzydamine hydrochloride were sprayed into the mouth initially 30 min before the operation and repeatedly 5 min before anaesthesia induction. For group D, two pastilles of dexpanthenol were administered orally to be sucked 30 min before the operation. For group P, four puffs of distilled water were sprayed into the mouth initially 30 min before the operation. Post-operatively, patients were evaluated for a sore throat for the duration of 24 h.

RESULTS

The incidence of a sore throat was significantly lower for group D when compared with group B and group P. The incidence of a sore throat was similar for group B and group P. According to the sore throat grading system, the number of patients experiencing no complaints was significantly higher for group D when compared with group B and group P. The number of patients achieving moderate scores was significantly higher for group B when compared with group D.

CONCLUSION

The administration of 200 mg of dexpanthenol prophylactically before endotracheal intubation is effective in the prevention of post-operative sore throat.

Rate of metoclopramide infusion affects the severity and incidence of akathisia

OBJECTIVE

To investigate the effect of the rate of metoclopramide infusion on akathisia incidence, severity, onset of symptoms, and duration in patients with headache, and/or nausea/vomiting in the emergency department (ED) setting.

METHODS

Prospective, double blind, randomised clinical study comparing two rates of intravenous infusion of metoclopramide over a period of six months at a tertiary university hospital ED.

RESULTS

A total of 300 patients presented to the ED met the inclusion criteria: 151 (50.3%) with nausea/vomiting, 108 (36%) with headache, and 41 (13.7%) with headache and nausea/vomiting. Of these, 154 patients (51.3%) were given 10 mg metoclopramide as a slow intravenous infusion over 15 minutes plus placebo (SIG group) and 146 patients were given 10 mg metoclopramide intravenous bolus infusion over two minutes plus placebo (BIG group). Nine of the 154 patients in the SIG group (5.8%) had akathisia compared with 36/146 patients (24.7%) in the BIG group (p < 0.001, OR 5.273, 95% CI 2.43 to 11.403). Severe akathisia were observed in 13/45 (28.8%). The incidence of severe akathisia was significantly higher in the BIG group (30.5%; 11/36) than in the SIG group (22.2%; 2/9), p = 0.009. Metoclopramide successfully relieved the presenting symptom(s) of 137/146 (90.8%) and 139/154 (90.2%) patients in the BIG and SIG groups, respectively.

CONCLUSIONS

This study suggests that slowing the rate of infusion of metoclopramide is an effective strategy for reducing the incidence of akathisia in patients with headache, and/or nausea/vomiting in ED.

Comparison of propofol-alfentanil and propofol-remifentanil anaesthesia in percutaneous nephrolithotripsy

BACKGROUND AND OBJECTIVE

Percutaneous nephrolithotripsy (PCNL) is used for the fragmentation and removal of stones from the renal pelvis and renal calyceal systems. We compared the effects of propofol-alfentanil or propofol-remifentanil anaesthesia on haemodynamics, recovery characteristics and postoperative analgesic requirements during percutaneous nephrolithotripsy.

METHODS

Thirty non-premedicated patients were randomly allocated to receive either propofol-alfentanil (Group A) or propofol-remifentanil (Group R). The loading dose of the study drug was administered over 60 s (alfentanil 10 microg kg(-1) or remifentanil 1 microg kg(-1)) followed by a continuous infusion (alfentanil 15 microg kg(-1) h(-1) or remifentanil 0.15 microg kg(-1) min(-1)). Propofol was administered until loss of consciousness and maintained with a continuous infusion of 75 microg kg(-1) min(-1) in both groups. Atracurium was given for endotracheal intubation at a dose of 0.5 mg kg(-1) and maintained with a continuous infusion of 0.4 mg kg(-1) h(-1). Mean arterial pressure heart rate, the total amount of propofol, time of recovery of spontaneous ventilation, extubation and eye opening in response to verbal stimulus and analgesic requirement were recorded.

RESULTS

In Group A, mean arterial pressure was higher at the first minute in the prone position, and during skin incision and lithotripsy, and heart rate was higher during skin incision and lithotripsy when compared with Group R (P < 0.05). The total amount of propofol did not differ between groups. Time of recovery of spontaneous ventilation, extubation and eye opening were significantly shorter in Group R than Group A (P < 0.05).

CONCLUSIONS

Both propofol-remifentanil and propofol-alfentanil anaesthesia provided stable haemodynamics during percutaneous nephrolithotripsy, whereas propofol-remifentanil allowed earlier extubation.

Prospective, randomised, double blind, controlled comparison of metoclopramide and pethidine in the emergency treatment of acute primary vascular and tension type headache episodes

STUDY OBJECTIVE

To compare analgesic effects of metoclopramide (MTP), pethidine (PET), and combination of metoclopramide-pethidine (M-PET) in the treatment of adult patients with acute primary vascular and tension type headache admitted in the emergency department (ED).

METHODS

All consecutive adult patients admitted into a university hospital ED in six months with acute vascular and tension type headache were recruited. The patients whose complaints had lasted no longer than seven days were randomised to four groups and thereby received 10 mg MTP intravenously plus placebo intramuscularly (MTP), 10 mg MTP intravenously plus 50 mg PET intramuscularly (M-PET), 50 mg PET intramuscularly plus placebo intravenously (PET); and intramuscular and intravenous placebo (PLC) in a blinded fashion. The patients were asked to report the degree of pain at 0, 15, 30, and 45 minutes on visual analogue scale (VAS) and demographic data and any side effects encountered were recorded. Rescue medication was used if required by the patient because of poor pain relief.

RESULTS

Data regarding 336 patients meeting inclusion criteria were analysed. Mean VAS values recorded at 45 minutes were significantly higher in PLC group than in others (p = 0.000). When the PLC group was excluded, VAS scores in MTP and M-PET groups were significantly lower than in PET group (p = 0.038). Though unimportant, the incidence of side effects recorded in PET group was found to be significantly higher than in the other groups (p = 0.003).

CONCLUSION

These data suggest that MTP produces more effective analgesia than PET in both vascular and tension type headache in patients with acute primary headache episodes.

Effects of fentanyl on the incidence of emergence agitation in children receiving desflurane or sevoflurane anaesthesia

BACKGROUND AND OBJECTIVE

In children, emergence agitation frequently complicates sevoflurane and desflurane anaesthesia. The effect of intravenous fentanyl 2.5 microg kg(-1) was examined on the incidence of emergence agitation in children who received desflurane or sevoflurane after midazolam premedication and intravenous thiopental induction.

METHODS

One hundred and twenty children (2-7 yr) undergoing adenoidectomy or tonsillectomy, or both, were studied. All children were premedicated orally with midazolam 0.5 mg kg(-1). After intravenous induction with thiopental and atracurium to facilitate endotracheal intubation, patients were randomly assigned to one of four groups: Patients in Groups 1 and 3 received physiological saline solution, whereas patients in Groups 2 and 4 received intravenous fentanyl 2.5 microg kg(-1) during induction. Anaesthesia was maintained with sevoflurane in Groups 1 and 2 and with desflurane in Groups 3 and 4. After discontinuation of the volatile anaesthetic, the times to tracheal extubation and response to verbal stimuli (emergence time), and emergence behaviours were recorded.

RESULTS

The time to tracheal extubation was significantly shorter in Groups 3 (5.2+/-1.7 min) and (6.4+/-2.1 min) than in Groups 1 (8.1+/-2.1 min) (P = 0.0001 and 0.006, respectively) and 2 (8.8+/-1.9 min) (P = 0.0001). The emergence time was significantly shorter in Group 3 (10.0+/-3.9 min) than in Groups 1 (13.8+/-4.9 min) (P = 0.017) and 2 (14.9+/-4.1 min) (P = 0.003). The incidence rate of severe agitation was 13% in Groups 1 and 3, and 7 and 10% in Groups 2 and 4, respectively (P > 0.05).

CONCLUSIONS

After midazolam premedication and intravenous induction of anaesthesia with thiopental administration of intravenous fentanyl 2.5 microg kg(-1) did not provide any clinically significant benefit on emer gence agitation in children who receive sevoflurane or desflurane anaesthesia.

Carbon dioxide pneumothorax during laparoscopic surgery

BACKGROUND

Anesthetic considerations for laparoscopic cholecystectomy are similar to those for other laparoscopic procedures and result from the creation of a pneumoperitoneum by insufflation of carbon dioxide (CO 2) into the abdominal cavity. The resultant problems such as decreased functional residual capacity, increased airway pressure, hypercarbia, and circulatory impairment are well known [1]. The reported case is that of a healthy 45-yr-old man who underwent elective laparoscopic cholecystectomy under general anesthesia. As surgery proceeded he developed hypercapnia (arterial blood partial pressure of CO 2 [pCO] 2], 97.1 mmHg; extrapolated end-tidal CO 2 tension [P ETCO 2], 90 mmHg) and hypoxemia (partial pressure of oxygen [pO 2], 53.1 mmHg). The cause was attributed to absorption of CO 2 directly related to the surgical pneumoperitoneum. This report illustrates the diagnosis and management of an unusual case of CO 2 absorption, resulting in hypercapnia and hypoxemia, and a spontaneous recovery within 30 to 60 min without need of thoracentesis.

Identification of beta-glucosidase aggregating factor (BGAF) and mapping of BGAF binding regions on Maize beta -glucosidase

In certain maize genotypes (nulls), beta-glucosidase does not enter the gel and therefore cannot be detected on zymograms. Such genotypes were initially thought to be homozygous for a null allele at the glu1 gene. We have shown that a beta-glucosidase aggregating factor (BGAF) is responsible for the null phenotype, and it specifically interacts with maize beta-glucosidases and forms large insoluble aggregates. To understand the mechanism of the beta-glucosidase-BGAF interaction, we constructed chimeric enzymes by domain swapping between the maize beta-glucosidase isozymes Glu1 and Gu2, to which BGAF binds, and the sorghum beta-glucosidase (dhurrinase) isozyme Dhr1, to which BGAF does not bind. The results of binding assays with 12 different chimeric enzymes showed that an N-terminal region (Glu(50)-Val(145)) and an extreme C-terminal region (Phe(466)-Ala(512)) together form the BGAF binding site on the enzyme surface. In addition, we purified BGAF, determined its N-terminal sequence, amplified the BGAF cDNA by reverse transcriptase-polymerase chain reaction, expressed it in Escherichia coli, and showed that it encodes a protein whose binding and immunological properties are identical to the native BGAF isolated from maize tissues. A data base search revealed that BGAF is a member of the jasmonite-induced protein family. Interestingly, the deduced BGAF sequence contained an octapeptide sequence (G(P/R)WGGSGG) repeated twice. Each of these repeat units is postulated to be involved in forming a site for binding to maize beta-glucosidases and thus provides a plausible explanation for the divalent function of BGAF predicted from binding assays.

Crystal structure of a monocotyledon (maize ZMGlu1) beta-glucosidase and a model of its complex with p-nitrophenyl beta-D-thioglucoside

The maize beta-glucosidase isoenzymes ZMGlu1 and ZMGlu2 hydrolyse the abundant natural substrate DIMBOAGlc (2-O-beta-D-glucopyranosyl-4-hydroxy-7-methoxy-1,4-benzoxazin-3-one), whose aglycone DIMBOA (2,4-hydroxy-7-methoxy-1,4-benzoxazin-3-one) is the major defence chemical protecting seedlings and young plant parts against herbivores and other pests. The two isoenzymes hydrolyse DIMBOAGlc with similar kinetics but differ from each other and their sorghum homologues with respect to specificity towards other substrates. To gain insights into the mechanism of substrate (i.e. aglycone) specificity between the two maize isoenzymes and their sorghum homologues, ZMGlu1 was produced in Escherichia coli, purified, crystallized and its structure solved at 2.5 Angstrom resolution by X-ray crystallography. In addition, the complex of ZMGlu1 with the non-hydrolysable inhibitor p-nitrophenyl beta-D-thioglucoside was crystallized and, based on the partial electron density, a model for the inhibitor molecule within the active site is proposed. The inhibitor is located in a slot-like active site where its aromatic aglycone is held by stacking interactions with Trp-378. Whereas some of the atoms on the non-reducing end of the glucose moiety can be modelled on the basis of the electron density, most of the inhibitor atoms are highly disordered. This is attributed to the requirement of the enzyme to accommodate two different species, namely the substrate in its ground state and in its distorted conformation, for catalysis.

The mechanism of substrate (aglycone) specificity in beta -glucosidases is revealed by crystal structures of mutant maize beta -glucosidase-DIMBOA, -DIMBOAGlc, and -dhurrin complexes

The mechanism and the site of substrate (i.e., aglycone) recognition and specificity were investigated in maize beta-glucosidase (Glu1) by x-ray crystallography by using crystals of a catalytically inactive mutant (Glu1E191D) in complex with the natural substrate 2-O-beta-d-glucopyranosyl-4-hydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOAGlc), the free aglycone DIMBOA, and competitive inhibitor para-hydroxy-S-mandelonitrile beta-glucoside (dhurrin). The structures of these complexes and of the free enzyme were solved at 2.1-, 2.1-, 2.0-, and 2.2-A resolution, respectively. The structural data from the complexes allowed us to visualize an intact substrate, free aglycone, or a competitive inhibitor in the slot-like active site of a beta-glucosidase. These data show that the aglycone moiety of the substrate is sandwiched between W378 on one side and F198, F205, and F466 on the other. Thus, specific conformations of these four hydrophobic amino acids and the shape of the aglycone-binding site they form determine aglycone recognition and substrate specificity in Glu1. In addition to these four residues, A467 interacts with the 7-methoxy group of DIMBOA. All residues but W378 are variable among beta-glucosidases that differ in substrate specificity, supporting the conclusion that these sites are the basis of aglycone recognition and binding (i.e., substrate specificity) in beta-glucosidases. The data also provide a plausible explanation for the competitive binding of dhurrin to maize beta-glucosidases with high affinity without being hydrolyzed.

The aglycone specificity-determining sites are different in 2, 4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA)-glucosidase (Maize beta -glucosidase) and dhurrinase (Sorghum beta -glucosidase)

The maize beta-glucosidase isozyme Glu1 hydrolyzes a broad spectrum of substrates in addition to its natural substrate DIMBOAGlc (2-O-beta-d-glucopyranosyl-4-hydroxy-7-methoxy-1,4-benzoxazin-3-on e), whereas the sorghum beta-glucosidase isozyme Dhr1 hydrolyzes exclusively its natural substrate dhurrin (p-hydroxy-(S)-mandelonitrile-beta-d-glucose). To study the mechanism of substrate specificity further, eight chimeric beta-glucosidases were constructed by replacing peptide sequences within the C-terminal region of Glu1 with the homologous peptide sequences of Dhr1 or vice versa, where the two enzymes differ by 4 to 22 amino acid substitutions, depending on the length of the swapped regions. Five Glu1/Dhr1 chimeras hydrolyzed substrates that are hydrolyzed by both parental enzymes, including dhurrin, which is not hydrolyzed by Glu1. In contrast, three Dhr1/Glu1 chimeras hydrolyzed only dhurrin but with lower catalytic efficiency than Dhr1. Additional domain-swapping within the C-terminal domain of Glu1 showed that replacing the peptide (466)FAGFTERY(473) of Glu1 with the homologous peptide (462)SSGYTERF(469) of Dhr1 or replacing the peptide (481)NNNCTRYMKE(490) in Glu1 with the homologous peptide (477)ENGCERTMKR(486) of Dhr1 was sufficient to confer to Glu1 the ability to hydrolyze dhurrin. Data from various reciprocal chimeras, sequence comparisons, and homology modeling suggest that the Dhr1-specific Ser-462-Ser-463 and Phe-469 play a key role in dhurrin hydrolysis. Similar data suggest that DIMBOAGlc hydrolysis determinants are not located within the extreme 47-amino acid-long C-terminal domain of Glu1.

Expression of soluble and catalytically active plant (monocot) beta-glucosidases in E. coli

Complementary DNAs encoding mature beta-glucosidase proteins Glu1 and Glu2 of maize were amplified by the polymerase chain reaction (PCR) and cloned into the expression vector pET21a. Both Glu1 and Glu2 isozymes were expressed in high yield ( approximately 3.8% of the total soluble protein and 32% of the total expressed protein) in E. coli. Recombinant enzymes were active on a variety of artificial and natural substrates at levels similar to those of their native counterparts isolated from maize seedlings. Western blot analysis confirmed that both recombinant isozymes were immunoreactive with maize anti-beta-glucosidase sera and their molecular sizes were identical to those of the native maize Glu1 and Glu2 isozymes. Zymogram assays in native gels revealed that recombinant enzymes had the same electrophoretic mobility and substrate specificity as their native counterparts.

Structure and expression of a dhurrinase (beta-glucosidase) from sorghum

Sorghum (Sorghum bicolor L. Moench) has two isozymes of the cyanogenic beta-glucosidase dhurrinase: dhurrinase-1 (Dhr1) and dhurrinase-2 (Dhr2). A nearly full-length cDNA encoding dhurrinase was isolated from 4-d-old etiolated seedlings and sequenced. The cDNA has a 1695-nucleotide-long open reading frame, which codes for a 565-amino acid-long precursor and a 514-amino acid-long mature protein, respectively. Deduced amino acid sequence of the sorghum Dhr showed 70% identity with two maize (Zea mays) beta-glucosidase isozymes. Southern-blot data suggested that beta-glucosidase is encoded by a small multigene family in sorghum. Northern-blot data indicated that the mRNA corresponding to the cloned Dhr cDNA is present at high levels in the node and upper half of the mesocotyl in etiolated seedlings but at low levels in the root-only in the zone of elongation and the tip region. Light-grown seedling parts had lower levels of Dhr mRNA than those of etiolated seedlings. Immunoblot analysis performed using maize-anti-beta-glucosidase sera detected two distinct dhurrinases (57 and 62 kD) in sorghum. The distribution of Dhr activity in different plant parts supports the mRNA and immunoreactive protein data, suggesting that the cloned cDNA corresponds to the Dhr1 (57 kD) isozyme and that the dhr1 gene shows organ-specific expression.