The role of CRE1 in nucleosome positioning within the cbh1 promoter and coding regions of Trichoderma reesei

Nucleosome positioning within the promoter and coding regions of the cellobiohydrolase-encoding cbh1 gene of Trichoderma reesei was investigated. T. reesei is a filamentous fungus that is able to degrade dead plant biomass by secreting enzymes such as cellulases, a feature which is exploited in industrial applications. In the presence of different carbon sources, regulation of one of these cellulase-encoding genes, cbh1, is mediated by various transcription factors including CRE1. Deletion or mutation of cre1 caused an increase in cbh1 transcript levels under repressing conditions. CRE1 was shown to bind to several consensus recognition sequences in the cbh1 promoter region in vitro. Under repressing conditions (glucose), the cbh1 promoter and coding regions are occupied by several positioned nucleosomes. Transcription of cbh1 in the presence of the inducer sophorose resulted in a loss of nucleosomes from the coding region and in the re-positioning of the promoter nucleosomes which prevents CRE1 from binding to its recognition sites within the promoter region. Strains expressing a non-functional CRE1 (in strains with mutated CRE1 or cre1-deletion) exhibited a loss of positioned nucleosomes within the cbh1 coding region under repressing conditions only. This indicates that CRE1 is important for correct nucleosome positioning within the cbh1 coding region under repressing conditions.

Yeast identification: reassessment of assimilation tests as sole universal identifiers

AIMS

To assess whether assimilation tests in isolation remain a valid method of identification of yeasts, when applied to a wide range of environmental and spoilage isolates.

METHODS AND RESULTS

Seventy-one yeast strains were isolated from a soft drinks factory. These were identified using assimilation tests and by D1/D2 rDNA sequencing. When compared to sequencing, assimilation test identifications (MicroLog™) were 18·3% correct, a further 14·1% correct within the genus and 67·6% were incorrectly identified. The majority of the latter could be attributed to the rise in newly reported yeast species.

CONCLUSIONS

Assimilation tests alone are unreliable as a universal means of yeast identification, because of numerous new species, variability of strains and increasing coincidence of assimilation profiles. Assimilation tests still have a useful role in the identification of common species, such as the majority of clinical isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

It is probable, based on these results, that many yeast identifications reported in older literature are incorrect. This emphasizes the crucial need for accurate identification in present and future publications.

Methanogenesis from ethanol by defined mixed continuous cultures

Methanogenesis from ethanol by defined mixed continuous cultures was studied. Under sulfate-free conditions, a Desulfovibrio strain was used as the ethanol-degrading species producing acetic acid and hydrogen. In a two-membered mutualistic coculture, the hydrogen was converted to methane by a Methanobacterium sp. and pH was maintained at neutrality by the addition of alkali. Introduction of a third species, the acetate-utilizing Methanosarcina mazei, obviated the need for external pH control. Methanogenesis by the co-and triculture was studied at various dilution rates in the steady state. The mutualistic coculture performed like a composite single species, as predicted from the theory of mutualistic interactions. Coupling between the mutualistic coculture and the acetate-utilizing methanogen was less tight. Increasing the dilution rate destabilized the triculture; at low dilution rates, instability was soon recovered, but at higher dilution rates imbalance between the rates of production and removal of acetic acid led to a drop in pH. Flocs formed in the triculture. An annulus of the Methanobacterium sp. and Desulfovibrio sp. was retained around the Methanosarcina sp. by strands of material probably derived from the Methanosarcina sp.

Detection and quantitation of methanogens by enzyme-linked immunosorbent assay

Antisera to two methanogenic bacteria, Methanosarcina barkeri and a Methanobacterium sp., were raised in rabbits and used to develop an enzyme-linked immunosorbent assay (ELISA) method. ELISA was shown to be a sensitive technique, detecting as little as 4 ng of methanogen protein. The specificities of the antisera toward other methanogens were evaluated, and it was found that the antisera recognized species of the same genus as the immunizing species, but gave very little cross-reaction with methanogens of different genera. ELISA was used to estimate the growth of methanogens in pure culture. In natural environments and in anaerobic digesters methanogens exist as part of a mixed bacterial community, so the possibility of using ELISA to quantitate methanogens in mixed cultures was examined. The two antisera gave very little reaction in ELISA when non-methanogenic bacteria were used as antigens and ELISA was used to quantitate methanogens in an acetate enrichment culture. I conclude that the ELISA is a useful method for quantitating methanogens in defined mixed cultures, but has limited applicability to more complex systems.

Uncoupling of Methanogenesis from Growth of Methanosarcina barkeri by Phosphate Limitation

Production of methane by Methanosarcina barkeri from H(2)-CO(2) was studied in fed-batch culture under phosphate-limiting conditions. A transition in the kinetics of methanogenesis from an exponentially increasing rate to a constant rate was due to depletion of phosphate from the medium. The period of exponentially increasing rate of methanogenesis was extended by increasing the initial concentration of phosphate in the medium. Addition of phosphate during the constant period changed the kinetics to an exponentially increasing rate of methanogenesis, indicating the reversibility of phosphate depletion. The relation between methanogenesis and growth of M. barkeri was investigated by measuring the incorporation of phosphorus, supplied as KH(2)PO(4), in the medium. At a low (1 muM) initial concentration of phosphate in the medium and during the constant period of methanogenesis, there was no net cell growth. At a higher (10 muM) initial concentration of phosphate, cell growth proceeded linearly with time after phosphate had been removed from the medium by uptake into cells.

SOD1-targeted gene disruption in the ericoid mycorrhizal fungus Oidiodendron maius reduces conidiation and the capacity for mycorrhization

The genome sequences of mycorrhizal fungi will provide new opportunities for studying the biology and the evolution underlying this symbiotic lifestyle. The generation of null mutants at the wild-type loci is one of the best methods for gene-function assignment in the post-genomic era. To our knowledge, the generation of superoxide dismutase 1 (SOD1)-null mutants in the ericoid mycorrhizal fungus Oidiodendron maius is the first example of a gene-targeted disruption via homologous recombination in a mycorrhizal fungus. The disruption of OmSOD1 by Agrobacterium-mediated transformation resulted in the presence of oxidative stress markers, even in the absence of external superimposed stresses, and an increased sensitivity to reactive oxygen species (ROS)-generating substances, especially to menadione. A reduction in conidiation and in the percentage of mycorrhization of Vaccinium myrtillus roots was also observed. The latter findings establish the pivotal role of SOD1 as an important factor in the relationship between O. maius and its symbiotic partner. The lack of this ROS-scavenger may cause an imbalance in the redox homeostasis during host colonization and an alteration in the delicate dialogue between the fungus and its host plant.

Modulation of chaperone gene expression in mutagenized Saccharomyces cerevisiae strains developed for recombinant human albumin production results in increased production of multiple heterologous proteins

The yeast Saccharomyces cerevisiae has been successfully established as a commercially viable system for the production of recombinant proteins. Manipulation of chaperone gene expression has been utilized extensively to increase recombinant protein production from S. cerevisiae, focusing predominantly on the products of the protein disulfide isomerase gene PDI1 and the hsp70 gene KAR2. Here we show that the expression of the genes SIL1, LHS1, JEM1, and SCJ1, all of which are involved in regulating the ATPase cycle of Kar2p, is increased in a proprietary yeast strain, developed by several rounds of random mutagenesis and screening for increased production of recombinant human albumin (rHA). To establish whether this expression contributes to the enhanced-production phenotype, these genes were overexpressed both individually and in combination. The resultant strains showed significantly increased shake-flask production levels of rHA, granulocyte-macrophage colony-stimulating factor, and recombinant human transferrin.

Spore germination in Mortierella alpina is associated with a transient depletion of arachidonic acid and induction of fatty acid desaturase gene expression

Mortierella alpina is an oleaginous filamentous fungus whose vegetative mycelium is known to accumulate triglyceride oil containing large amounts of arachidonic acid (ARA 20:4, n - 6). We report that the spores of Mortierella alpina also contain a large proportion of ARA, comprising 50% of total fatty acid. Fatty acid desaturase genes were not expressed in dormant spores but were induced during germination, following a significant drop in the level of ARA (down from 50% of total fatty acid to 12%) prior to germ-tube emergence. We propose that ARA serves as a reserve supply of carbon and energy that is utilised during the early stages of spore germination in Mortierella alpina.

UPR-independent dithiothreitol stress-induced genes in Aspergillus niger

A subtraction library was prepared from cultures of Aspergillus niger that had or had not been exposed to dithiothreitol (DTT), in order to identify genes involved in the unfolded protein response (UPR) or in the response to reductive stress. A large fraction of the clones in the library (40%) encoded two putative methyltransferases (MTs) whose function has yet to be determined. Other stress-responsive genes included a homologue of the Mn2+-containing superoxide dismutase gene (sodB) and a number of genes predicted to code for products that function in protein turnover and in intra- and extracellular transport of molecules. Transcriptional microarray analysis was carried out with a group of 15 genes, comprising 11 from the cDNA library, two genes linked to the putative MT genes but not represented in the library, and two UPR control genes (bipA and pdiA). Eleven of the 15 genes were inducible with DTT. This was either reflected by the presence of transcripts in cells subjected to DTT stress compared to absence under control conditions, or by an induction ratio of between 1.4 and 8.0 in cases where transcripts were already detectable under control conditions. The MT genes were among the four most highly induced. None of the genes, apart from bipA and pdiA, showed significant induction in response to other stresses that are known to induce the UPR in fungi. We conclude that DTT alone does not provide for specific induction of UPR genes and that other stress conditions must also be examined.

A preliminary analysis of the process of protein secretion and the diversity of putative secreted hydrolases encoded inAspergillus fumigatus: insights from the genome

The genome sequence of Aspergillus fumigatus has enabled the annotation of genes likely to encode secreted enzymes that may be important in underpinning the natural lifestyle of the fungus and its pathogenicity. We summarize the data from the genome sequence relevant to both the process of protein secretion and the predicted hydrolase enzymes secreted by A. fumigatus.

Chloroquine causes lysosomal dysfunction in neural retina and RPE: implications for retinopathy

Chronic use of chloroquine has been shown to induce numerous pathophysiological defects in the retina. This drug has the ability to alter pH of intracellular compartments and lysosomal function of the retinal pigment epithelium (RPE) and retinal neurons may constitute the basis of chloroquine retinopathy. The aim of the current study was to investigate pathogenic alterations in retinal cells continuously exposed to chloroquine using appropriate in vivo and in vitro models. Male hooded Lister rats were implanted with osmotic mini pumps which released chloroquine continuously over a period of seven days. The eyes were processed for electron microscopy and ultrastructural abnormalities determined in the neural retina and quantified using stereology in the retinal pigment epithelium (RPE). RPE were also exposed to chloroquine in vitro and lysosomal pH changes were investigated using a pH sensitive probe. Degradative capacity was also analysed using FITC labeled rod outer segments (ROS). Chloroquine-treated animals displayed several ultrastructural abnormalities including numerous membranous cytoplasmic bodies (MCBs) in retinal neurons. Cone photoreceptors displayed numerous MCBs although rods did not. The RPE of the treated groups all showed significantly higher numbers of lysosomal associated organelles (LAO) than the control group (p < 0.001). The in vitro experiments demonstrated chloroquine-mediated rises in lysosomal pH and an increase in lysosome/phagosome accumulation of ROS in the chloroquine treated group (p < 0.01). The current study demonstrates that chloroquine disrupts lysosomal function in retinal neurons and RPE. The evidence presented provides a clear pathogenic basis for the functional defects experienced by patients with chloroquine retinopathy.

Prevention of retinal capillary basement membrane thickening in diabetic dogs by a non-steroidal anti-inflammatory drug

AIMS/HYPOTHESIS

To investigate the effect of treatment with the non-steroidal anti-inflammatory drug Sulindac on the early vascular pathology of diabetic retinopathy in the dog, and it's effect on recognised biochemical indices of hyperglycaemia-related pathophysiology.

METHODS

Experimental diabetes (streptozotocin/alloxan) was induced in 22 male beagle dogs and 12 of the animals were assigned at random to receive oral Sulindac (10 mg/kg daily). Age- and sex-matched control animals were maintained as non-diabetic controls. After 4 years, several morphological parameters were quantified in the retinal microvasculature of each animal group using an established stereological method. Also, the following diabetes-associated biochemical parameters were analysed: accumulation of advanced glycation end products (AGEs), red blood cell polyol levels and antioxidant status.

RESULTS

Diabetes increased red blood cell sorbitol levels when compared to non-diabetic controls (p< or =0.05), however, there was no difference in sorbitol levels between the untreated and the treated diabetic animals. No significant differences were found in red blood cell myoinositol levels between the three groups of animals. Pentosidine and other AGEs were increased two- to three-fold in the diabetic animals (p< or =0.001) although treatment with Sulindac did not affect their accumulation in diabetic skin collagen or alter diabetes-induced rises in plasma malondialdehyde. Retinal capillary basement membrane volume was significantly increased in the untreated diabetic dogs compared to non-diabetic controls or Sulindac-treated diabetic animals (p< or =0.0001).

CONCLUSION/INTERPRETATION

This study has confirmed the beneficial effect of a non-steroidal anti-inflammatory drug on the early vascular pathology of diabetic retinopathy. However the treatment benefit was not dependent on inhibition of polyol pathway activity, advanced glycation, or oxidative stress.

In vitro stability and immunoreactivity of the native and recombinant plant food 2S albumins Ber e 1 and SFA-8

BACKGROUND

The ability of an intact protein to reach the circulatory system may be a prerequisite to allergenicity and many allergens, particularly those from plant foods, have been found to be consistently more resistant to digestion by pepsin than other proteins.

OBJECTIVE

This study assessed the pepsinolytic stability of native 2S albumins from Brazil nut and sunflower seed and their recombinant versions produced in Pichia pastoris. The physicochemical stability of native and recombinant Brazil nut 2S albumins and recombinant sunflower seed 2S albumin was also assessed. The immunoreactivity of native Brazil nut 2S albumin and recombinant 2S albumins was compared using serum from patients allergic to Brazil nuts and animals immunized with native 2S albumins.

METHODS

Digestibility was measured in simulated gastric fluid followed by SDS-PAGE. Circular dichroism spectra were used to analyse unfolding, as proteins were denatured by temperature, pH and guanidinium chloride. Immunoreactivity was assessed by immunoblot, RAST and ELISA.

RESULTS

Brazil nut 2S albumin was significantly more resistant to proteolytic digestion than other Brazil nut proteins. It was also resistant to thermally and chemically induced denaturation. Equally high resistance to proteolytic digestion was observed with sunflower seed 2S albumin. The recombinant albumins mirrored their native counterparts in stability and immunoreactivity.

CONCLUSION

The important food allergen Brazil nut 2S albumin is as stable to digestion as is sunflower seed 2S albumin, whose allergenicity has yet to be determined. The 2S albumins and their recombinant counterparts could not be easily denatured by physicochemical treatments. The results suggest that 2S albumin is the only Brazil nut protein to reach the gut immune system intact. The production of properly folded recombinant proteins will facilitate mechanistic studies as well as diagnostic testing and antigen-based therapies.

Comparison of modular and non-modular xylanases as carrier proteins for the efficient secretion of heterologous proteins from Penicillium funiculosum

Genes encoding three enzymes with xylanase activity from the filamentous fungus Penicillium funiculosum are described. Two of the encoded xylanases are predicted to be modular in structure with catalytic and substrate-binding domains separated by a serine and threonine-rich linker region; the other had none of these properties and was non-modular. In order to develop P. funiculosum as a host for the secreted production of heterologous proteins, each of the xylanases was assessed for use as a carrier protein in a fusion strategy. We show that one of the modular xylanases (encoded by xynA) was an effective carrier protein but the other (encoded by xynB) and the non-modular xylanase (encoded by xynC) were not effective as secretion carriers. We show that the beta-glucuronidase (GUS) protein from Escherichia coli is secreted by P. funiculosum when expressed as an XYNA fusion but that the secreted GUS protein, cleaved in vivo from XYNA, is glycosylated and enzymatically inactive.

Isolation and characterisation of a calnexin homologue, clxA, from Aspergillus niger

We describe the isolation of a gene (clxA) encoding calnexin from laboratory and industrial strains of Aspergillus niger. Calnexin is a chaperone, which specifically recognises monoglucosylated glycoproteins in the endoplasmic reticulum, and is thus an essential component of the process that assesses the folded state of nascent secreted glycoproteins. Manipulation of chaperones has previously been adopted in attempts to overcome some of the problems associated with the secretion of heterologous proteins from filamentous fungi. The A. niger clxA gene encodes a 562-residue protein with strong homology to the calnexin of Schizosaccharomyces pombe. The clxAgene product complements a S. pombe cnx1 mutant. Motifs associated with genes controlled via the Unfolded Protein Response (UPR) were identified by sequence homology in the promoter of clxA. Steady-state levels of clxA mRNA were elevated in a strain expressing bovine prochymosin fused to the catalytic domain of glucoamylase. The ORF is punctuated by four introns, and contains two sets of four repeated peptide motifs that are characteristic of the calnexin family, together with a putative membrane-spanning domain. Deletion studies indicate that clxA is not an essential gene in A. niger.

Use of a histone H4 promoter to drive the expression of homologous and heterologous proteins by Penicillium funiculosum

Two genes encoding histone H4 (H4.1 and H4.2) from Penicillium funiculosum have been cloned and characterised. Structurally, the histone H4.1 gene is divergently linked to the histone H3 gene and the two genes are separated by approximately 800 bp. The transcription of the histone H4.1 and H4.2 genes in P. funiculosum appears to be distinctively regulated. Histone H4.1 mRNA showed a high steady-state level during the early stages of batch culture that decreased as growth reached the stationary phase. In contrast, the expression of the histone H4.2 gene was lower than that of H4.1 throughout batch growth and increased gradually with time. In order to expand the industrial application of P. funiculosum as a host for the production of heterologous proteins, the promoter of the histone H4.1 gene was successfully used to drive the expression of an intracellular bacterial enzyme, beta-glucuronidase, and a secreted homologous enzyme, xylanase C. The constitutive secretion of xylanase C was achieved in the absence of other xylanases by batch fermentation in the presence of glucose.

Stability of recombinant 2 S albumin allergens in vitro

Two well known 2 S albumins, Ber e 1 from brazil nut and sunflower 2 S albumin 8 (SFA-8), have been expressed in a eukaryotic system and purified. Analysis of recombinant versions of Ber e 1 and SFA-8 revealed them to be significantly more resistant to digestion by pepsin than BSA, and to be stable for up to 30 min in simulated gastric fluid. Unfolding monitored by CD indicated that both proteins were also very resistant to denaturation induced by heat and low pH. These results suggest that, although the ability of 2 S albumins to reach the circulatory system may be a prerequisite for the allergenicity of this group of proteins, stability is just one of a number of characteristics that provoke a selective immune response.

Nerve pathology in the type 1 diabetic dog: effects of treatment with sulindac

The purpose of this study was to define pathological abnormalities in the peripheral nerve of a large animal model of long-duration type 1 diabetes and also to determine the effects of treatment with sulindac. Detailed morphometric studies were performed to define nerve fiber and endoneurial capillary pathology in 6 control dogs, 6 type 1 diabetic dogs treated with insulin, and 6 type 1 diabetic dogs treated with insulin and sulindac for 4 years. Myelinated fiber and regenerative cluster density showed a non-significant trend toward a reduction in diabetic compared to control animals, which was prevented by treatment with sulindac. Unmyelinated fiber density did not differ among groups. However, diabetic animals showed a non-significant trend toward an increase in axon diameter (p < 0.07), with a shift of the size frequency distribution towards larger axons, which was not prevented by treatment with sulindac. Endoneurial capillary density and luminal area showed a non-significant trend toward an increase in diabetic animals, which was prevented with sulindac treatment. Endoneurial capillary basement membrane area was significantly increased (p < 0.05) in diabetic animals, but was not prevented with sulindac treatment. We conclude that the type 1 diabetic dog demonstrates minor structural abnormalities in the nerve fibers and endoneurial capillaries of the sciatic nerve, and treatment with sulindac ameliorates some but not all of these abnormalities.

Ocular surface reconstruction in LOGIC syndrome by amniotic membrane transplantation

PURPOSE

To determine whether preserved amniotic membrane can be used to reconstruct the ocular surface after excision of the invading granulation material typical of LOGIC syndrome (laryngeal and ocular granulation tissue in children from the Indian subcontinent).

METHODS

Granulation tissue was dissected and excised from both eyes of a 10-year-old boy with LOGIC syndrome. This procedure was followed by coverage of the corneal, scleral, and subtarsal regions of each eye with amniotic membrane, which had been stored for 6 months at -70 degrees C.

RESULTS

Initial 2.5-month follow up demonstrated complete disappearance of granulation tissue. The fornices were patent, there was no recurrence of symblepharon, ocular inflammation was suppressed, and the patient reported markedly increased comfort. Both eyelids remained ptotic because of levator muscle atrophy secondary to many years of inability to open either eye. No residual scarring or evidence of granulation tissue was observed in that period. The 10-month follow up demonstrated limited recurrence, particularly where there was an intraoperative break in the amniotic membrane.

CONCLUSIONS

After 24 operations to treat the ocular complications induced by LOGIC syndrome, amniotic membrane transplantation was the first effective treatment. In the early follow up period (2-3 months), there was complete cessation of the proliferation of granulation tissue and reepithelialization of the corneal surface. Longer follow up (10 months) demonstrated limited recurrence, which will require retreatment.

A defined level of protein disulfide isomerase expression is required for optimal secretion of thaumatin by Aspegillus awamori

Thaumatin, a 22-kDa protein containing eight disulfide bonds, is secreted by the filamentous fungus Aspergillus awamori at levels which are dependent upon the extent of overexpression of protein disulfide isomerase (PDIA). Additional copies of the PDIA-encoding gene pdiA were introduced into a strain of A. awamori that expresses a cassette encoding thaumatin. Transformants with different levels of pdiA mRNA and measured PDIA levels were chosen for examination of the impact that PDIA levels had on thaumatin secretion. The secretion of two native proteins, alpha-amylase and acid phosphatase, was also examined in relation to varying levels of PDIA. Over a range of PDIA levels of 1-8, relative to the native level in strains with just one copy of the pdiA gene, the fraction of alpha-amylase and acid phosphatase in the total secreted protein was unaffected. In contrast, a peak level of thaumatin, about 5-fold higher than in the strain with one copy of pdiA, was found in strains with a relative PDIA level of between two and four. Improved thaumatin production was confirmed in 5-1 fermenters using a strain of A. awamori with six pdiA gene copies, containing 3.2-fold higher levels of PDIA than wild-type strains.

Residual visual functions of guide dog owners in the UK

Numbers of guide dog owners (GDOs) in the United Kingdom reached 4700 by the end of 1998. Despite this growing trend, little is known about the nature of their visual loss. This paper reports the results of a national three-centre investigation into the residual visual functions and ophthalmic conditions of guide dog owners. Random samples of GDOs (Scotland n = 82, England n = 77, and Northern Ireland n = 87) underwent a detailed visual analysis and interview. GDOs had an overall median age of 53 years. Nationally, they make up just 2.4% of the registered blind population. All GDOs were found to have profound loss of visual acuity, contrast sensitivity or visual fields, but only 43% were totally blind. GDOs in Scotland retained higher levels of residual visual function than those in the other two regions. The main causes of visual loss were congenital and early onset degenerative eye disease (retinitis pigmentosa 18%, optic atrophy 10%). Results taken in conjunction with epidemiological registration trends suggest that the past growth in numbers of GDOs is unlikely to be sustainable. Implications for mobility service providers are discussed. It is suggested that increased optometric input and a multidisciplinary approach could assist present and potential guide dog owners.

Protein-glutaminase from Chryseobacterium proteolyticum, an enzyme that deamidates glutaminyl residues in proteins. Purification, characterization and gene cloning

A novel protein-deamidating enzyme was purified to homogeneity from Chryseobacterium proteolyticum and the gene encoding it was cloned. The enzyme is a monomer with a pI of 10.0, a measured M(r) of approximately 20,000 and a calculated M(r) of 19,860. Extensive comparison with Streptoverticillium transglutaminase showed that the protein-deamidating enzyme lacked transglutaminase activity in terms of hydroxamate-formation between benzyloxycarbonyl-Gln-Gly and hydroxylamine, or monodansylcadaverine incorporation into casein. The enzyme deamidated the two glutaminyl residues in the oxidized insulin A chain and deamidated both casein and the oxidized insulin B chain with higher catalytic efficiencies (k(cat)/K(m)) than with short peptides. The enzyme was active against several proteins, including insoluble wheat gluten, but did not deamidate asparaginyl residues in peptides, free glutamine or other amides. The enzyme was therefore named protein-glutaminase (EC 3.5.1). The gene encoding the protein was cloned and, when expressed in Escherichia coli, the protein product had protein-glutaminase activity and cross-reacted with antiserum raised against the purified enzyme. The protein-glutaminase was shown to be expressed as a prepro-protein with a putative signal peptide of 21 amino acids and a pro-sequence of 114 amino acids. The amino-acid sequence had no obvious homology to any published sequence and is therefore a novel protein-glutaminase.

A modular esterase from Penicillium funiculosum which releases ferulic acid from plant cell walls and binds crystalline cellulose contains a carbohydrate binding module

An esterase was isolated from cultures of the filamentous fungus Penicillium funiculosum grown on sugar beet pulp as the sole carbon source. The enzyme (ferulic acid esterase B, FAEB) was shown to be a cinnamoyl esterase (CE), efficiently releasing hydroxycinnamic acids from synthetic ester substrates and plant cell walls, and bound strongly to microcrystalline cellulose. A gene fragment was obtained by PCR using partial amino-acid sequences obtained from the pure enzyme and used to a probe a P. funiculosum genomic DNA library. A clone containing a 1120-bp ORF, faeB, was obtained which encoded a putative 353-residue preprotein including an 18-residue signal peptide, which when expressed in Eschericia coli produced CE activity. Northern analysis showed that transcription of faeB was tightly regulated, being stimulated by growth of the fungus on sugar beet pulp but inhibited by free glucose. The faeB promoter sequence contains putative motifs for binding an activator protein, XLNR, and a carbon catabolite repressor protein, CREA. FAEB was comprised of two distinct domains separated by a 20 residue Thr/Ser/Pro linker region. The N-terminal domain comprised 276 amino acids, contained a G-X-S-X-G motif typical of serine esterases, and was shown to be a member of a family comprising serine esterases, including microbial acetyl xylan esterases, poly (3-hydroxyalkanoate) depolymerases and CEs, and proteins of unknown function from Mycobacterium spp. and plants. The C-terminal domain comprised 39 amino acids and closely resembled the family 1 cellulose binding carbohydrate-binding modules (CBM) of fungal glycosyl hydrolases. This is the first report of a fungal CE with a CBM.

Isolation and use of a homologous histone H4 promoter and a ribosomal DNA region in a transformation vector for the oil-producing fungus Mortierella alpina

Mortierella alpina was transformed successfully to hygromycin B resistance by using a homologous histone H4 promoter to drive gene expression and a homologous ribosomal DNA region to promote chromosomal integration. This is the first description of transformation in this commercially important oleaginous organism. Two pairs of histone H3 and H4 genes were isolated from this fungus. Each pair consisted of one histone H3 gene and one histone H4 gene, transcribed divergently from an intergenic promoter region. The pairs of encoded histone H3 or H4 proteins were identical in amino acid sequence. At the DNA level, each histone H3 or H4 open reading frame showed 97 to 99% identity to its counterpart but the noncoding regions had little sequence identity. Unlike the histone genes from other filamentous fungi, all four M. alpina genes lacked introns. During normal vegetative growth, transcripts from the two histone H4 genes were produced at approximately the same level, indicating that either histone H4 promoter could be used in transformation vectors. The generation of stable, hygromycin B-resistant transformants required the incorporation of a homologous ribosomal DNA region into the transformation vector to promote chromosomal integration.

Filamentous fungi as microbial cell factories for food use

The knowledge base that will underpin the more efficient use of filamentous fungi as cell factories in food has increased during the past year in the areas of gene regulation, protein secretion, safety and synthesis of ingredients such as long-chain polyunsaturated fatty acids.

A glucoamylase::GFP gene fusion to study protein secretion by individual hyphae of Aspergillus niger

Although Aspergillus niger is used as a host for heterologous protein production, yields are generally lower than those obtained for homologous proteins. Mechanisms of protein secretion and the secretory pathway in filamentous fungi are poorly characterised, although there is evidence to suggest that secretion occurs by a mechanism similar to that in other eukaryotes, but with proteins destined for secretion being directed to the hyphal tip. We report on a method using a glucoamylase: GFP gene fusion which allows us for the first time to monitor, in vivo, protein secretion in A. niger at the single hyphal level. A synthetic green fluorescent protein (sGFP(S65T)) was fused to truncated A. niger glucoamylase (GLA:499). Southern blot analysis of transformants confirmed that the gene fusion had successfully integrated into the A. niger genome. Confocal and fluorescence microscopy revealed that the GLA::GFP fusion protein is fluorescent in A. niger and appears to be directed to the hyphal tip. In young mycelia, hyphal cell wall fluorescence is apparent and immunogold labelling of GFP confirmed that GFP was partially localised within the hyphal cell wall. Using Western blotting, extracellular GLA::GFP was detected only in culture filtrates of young mycelia grown in a soya milk medium. The actin inhibitor latrunculin B was used to disrupt the secretion process, and its effects on the distribution of GLA::GFP were monitored.

Advanced glycation end products induce blood-retinal barrier dysfunction in normoglycemic rats

Advanced glycation end products (AGEs) have been implicated in the progressive vascular dysfunction which occurs during diabetic retinopathy. In the current study we have examined the role of these adducts in blood-retinal barrier (BRB) breakdown and investigated expression of the vasopermeabilizing agent vascular endothelial growth factor (VEGF) in the retina. When normoglycemic rats were injected with AGE-modified albumin daily for up to 10 days there was widespread leakage of FITC-dextran and serum albumin from the retinal vasculature when compared to control animals treated with nonmodified albumin. Ultrastructural examination of the vasculature revealed areas of attenuation of the retinal vascular endothelium and increased vesicular organelles only in the AGE-exposed rats. Quantitative RT-PCR and in situ hybridization demonstrated a significant increase in retinal VEGF mRNA expression (P < 0.05). These results suggest that AGEs can initiate BRB dysfunction in nondiabetic rats and a concomitant increase in retinal VEGF expression. These findings may have implications for the role of AGEs in the pathogenesis of diabetic retinopathy.

Amyloid fibril formation and seeding by wild-type human lysozyme and its disease-related mutational variants

Wild-type human lysozyme and its two stable amyloidogenic variants have been found to form partially folded states at low pH. These states are characterized by extensive disruption of tertiary interactions and partial loss of secondary structure. Incubation of the proteins at pH 2.0 and 37 degrees C (Ile56Thr and Asp67His variants) or 57 degrees C (wild-type) results in the formation of large numbers of fibrils over several days of incubation. Smaller numbers of fibrils could be observed under other conditions, including neutral pH. These fibrils were analyzed by electron microscopy, Congo red birefringence, thioflavine-T binding, and X-ray fiber diffraction, which unequivocally show their amyloid character. These data demonstrate that amyloidogenicity is an intrinsic property of human lysozyme and does not require the presence of specific mutations in its primary structure. The amyloid fibril formation is greatly facilitated, however, by the introduction of "seeds" of preformed fibrils to the solutions of the variant proteins, suggesting that seeding effects could be important in the development of systemic amyloidosis. Fibril formation by wild-type human lysozyme is greatly accelerated by fibrils of the variant proteins and vice versa, showing that seeding is not specific to a given protein. The fact that wild-type lysozyme has not been found in ex vivo deposits from patients suffering from this disease is likely to be related to the much lower population of incompletely folded states for the wild-type protein compared to its amyloidogenic variants under physiological conditions. These results support the concept that the ability to form amyloid is a generic property of proteins, but one that is mitigated against in a normally functioning organism.

Measurement of cellular repair activities for oxidative DNA damage

Two related assays capable of determining cell extract repair activities for different oxidative lesions in DNA are described. Both assays measure the incorporation of radiolabeled nucleotides during repair of an oxidatively damaged template in a cell-free system. The assays differ in the type of oxidative damage present in the DNA. In one, singlet oxygen is used to generate predominantly 8-oxo-2'-deoxyguanosine lesions. In the other, hydroxyl radicals are used to generate a broad spectrum of damage including oxidized bases and strand breaks. Assay conditions were adjusted to ensure that radiolabel incorporation was directly proportional to cell extract repair activity. These assays represent sensitive tools for investigating the regulation of repair systems for oxidative DNA damage.

Prevention of yeast spoilage in feed and food by the yeast mycocin HMK

The yeast Williopsis mrakii produces a mycocin or yeast killer toxin designated HMK; this toxin exhibits high thermal stability, high pH stability, and a broad spectrum of activity against other yeasts. We describe construction of a synthetic gene for mycocin HMK and heterologous expression of this toxin in Aspergillus niger. Mycocin HMK was fused to a glucoamylase protein carrier, which resulted in secretion of biologically active mycocin into the culture media. A partial purification protocol was developed, and a comparison with native W. mrakii mycocin showed that the heterologously expressed mycocin had similar physiological properties and an almost identical spectrum of biological activity against a number of yeasts isolated from silage and yoghurt. Two food and feed production systems prone to yeast spoilage were used as models to assess the ability of mycocin HMK to act as a biocontrol agent. The onset of aerobic spoilage in mature maize silage was delayed by application of A. niger mycocin HMK on opening because the toxin inhibited growth of the indigenous spoilage yeasts. This helped maintain both higher lactic acid levels and a lower pH. In yoghurt spiked with dairy spoilage yeasts, A. niger mycocin HMK was active at all of the storage temperatures tested at which yeast growth occurred, and there was no resurgence of resistant yeasts. The higher the yeast growth rate, the more effective the killing action of the mycocin. Thus, mycocin HMK has potential applications in controlling both silage spoilage and yoghurt spoilage caused by yeasts.

Molecular basis of glucoamylase overproduction by a mutagenised industrial strain of Aspergillus niger

We have compared a mutagenized strain of Aspergillus niger (S1), used industrially for glucoamylase production, and a related low glucoamylase-producing strain (S2) with a laboratory strain of A. niger (AB4.1). Our aim was to assess the properties of S1 in relation to the laboratory strain and to account at the molecular level for the basis of its glucoamylase overproduction. Both S1 and S2 have similar multiple copies of the glucoamylase-encoding gene (glaA) but only S1 has enhanced glaA transcript and glucoamylase levels compared to AB4.1 that has a single copy of the glaA gene. Glucoamylase production by S1 and AB4.1 was repressed by xylose and induced by starch but, in S2, remained unaffected by carbon source. S1 also secreted elevated levels of alpha-amylase relative to both S2 and AB4.1 but the production of alpha-glucosidase was low in all three strains. The gene encoding aspergillopepsin (pepA), an abundant secreted aspartyl protease, was present as a single copy in all strains but no aspergillopepsin could be detected by Western blotting in either S1 or S2 culture supernatants. We conclude that A. niger strain improvement by mutagenesis and screening for glucoamylase overproduction has led to glaA gene multiplication and an expression defect in the pepA gene.

Characterization of a foldase, protein disulfide isomerase A, in the protein secretory pathway of Aspergillus niger

Protein disulfide isomerase (PDI) is important in assisting the folding and maturation of secretory proteins in eukaryotes. A gene, pdiA, encoding PDIA was previously isolated from Aspergillus niger, and we report its functional characterization here. Functional analysis of PDIA showed that it catalyzes the refolding of denatured and reduced RNase A. pdiA also complemented PDI function in a Saccharomyces cerevisiae Deltapdi1 mutant in a yeast-based killer toxin assay. Levels of pdiA mRNA and PDIA protein were raised by the accumulation of unfolded proteins in the endoplasmic reticulum. This response of pdiA mRNA levels was slower and lower in magnitude than that of A. niger bipA, suggesting that the induction of pdiA is not part of the primary stress response. An increased level of pdiA transcripts was also observed in two A. niger strains overproducing a heterologous protein, hen egg white lysozyme (HEWL). Although overexpression of PDI has been successful in increasing yields of some heterologous proteins in S. cerevisiae, overexpression of PDIA did not increase secreted yields of HEWL in A. niger, suggesting that PDIA itself is not limiting for secretion of this protein. Downregulation of pdiA by antisense mRNA reduced the levels of microsomal PDIA activity by up to 50%, lowered the level of PDIA as judged by Western blots, and lowered the secreted levels of glucoamylase by 60 to 70%.

Comet assay of UV-induced DNA damage in retinal pigment epithelial cells

PURPOSE

The molecular mechanisms mediating photic injury to the retinal pigment epithelial (RPE) cell are not clearly understood. This study examined qualitative and quantitative aspects of DNA damage caused by broadband UVA and UVB radiation in RPE cells.

METHODS

Cultured bovine RPE cells were exposed to doses of between 0 and 0.9 J/cm2 UVA or 0 and 0.09 J/cm2 UVB, as either a suspension or as an attached monolayer. The damage to DNA resulting in single-strand breaks was assessed by means of the comet assay in which the damaged DNA migrates out of the nucleus forming a tail, and this was quantified using image analysis. Two measurements were taken: the mean percentage of tail DNA, which reflects the overall level of DNA damage in the group of cells, and the Olive tail moment, which represents the extent of migration and thus the pattern of DNA damage in individual cells. Cells were processed by the comet assay immediately after UV exposure in acute experiments. To study the occurrence of DNA repair, RPE cells were first exposed to UVB and then incubated at 37 degrees C for either 1 or 24 hours before processing for the comet assay.

RESULTS

UVA- and UVB-exposed cells showed a mean percentage of tail DNA that was significantly greater than in unexposed cells. Olive tail moment was higher in cells exposed to larger doses of UVB. This parameter also showed a bimodal distribution when assessed 24 hours after exposure to UVB indicating the presence of two distinct subpopulations of cells with small and large tail moments. Cells with very large tail moments were not seen with doses below 0.045 J/cm2.

CONCLUSIONS

Relatively low doses of UVA and UVB induce the formation of DNA strand breaks in cultured RPE. The tail moment profiles for cells incubated for 24 hours after UVB irradiation are consistent with the occurrence of DNA repair in most cells exposed to low doses and apoptosis in a subpopulation of the cells exposed to high doses.

Corneal guttata: a comparative clinical and specular micrographic study

BACKGROUND

The relationship between corneal guttata and Fuchs' endothelial dystrophy is unclear, with the result that the clinical differentiation of the two conditions is often made on the basis of the presence or absence of symptoms.

METHODS

In this study the authors compare the clinical and specular micrographic findings, as recorded from 20 patients noted to have biomicroscopic clinical findings consistent with corneal guttata or early Fuchs' endothelial dystrophy.

RESULTS

Results confirm the increased prevalence of corneal findings in elderly women. The topographical distribution of guttata, across the posterior corneal surface, as observed clinically was confirmed specular micrographically (rS = 0.55, p = 0.01). Increased numbers of guttata correlated with a statistically significant reduction in the endothelial cell counts recorded from the midperipheral cornea (rS = 0.49, p = 0.02). The relationship between the presence of guttata and a reduction in cellular hexagonality or an increase in polymegethism failed to reach a statistically significant level. Pigment deposits adherent to the posterior endothelial surface were also noted in all but one of the eyes examined.

CONCLUSIONS

The authors advocate the use of a grading scale, developed from specular micrographs taken during the course of the study, to assist in the clinical classification of corneal guttata and pre-clinical Fuchs' dystrophy. The authors also recommend specular microscopy as a tool capable of differentiating corneal guttata from pigment deposits in even the most severely affected cases.

Two fatty acid delta9-desaturase genes, ole1 and ole2, from Mortierella alpina complement the yeast ole1 mutation

Genes encoding two distinct fatty acid delta9-desaturases were isolated from strains of the oleaginous fungus Mortierella alpina. Two genomic sequences, delta9-1 and delta9-2, each containing a single intron, were cloned from strain CBS 528.72 while one cDNA clone, LM9, was isolated from strain CBS 210.32. The delta9-1 gene encoded a protein of 445 aa which shared 99% identity with the LM9 gene product. These proteins also showed 40-60% identity to the delta9-desaturases (Ole1p) of other fungi and contained the three conserved histidine boxes, C-terminal cytochrome b5 fusion and transmembrane domains characteristic of endoplasmic reticulum membrane-bound delta9-desaturases. LM9 and delta9-1 are therefore considered to represent the same gene (ole1). The ole1 gene was transcriptionally active in all M. alpina strains tested and its function was confirmed by complementation of the Saccharomyces cerevisiae ole1 mutation. Fatty acid analysis of yeast transformants expressing the CBS 210.32 ole1 gene showed an elevated level of oleic acid (18:1) compared to palmitoleic acid (16:1), the major fatty acid component of wild-type S. cerevisiae. This indicated that the M. alpina delta9-desaturase had a substrate preference for stearic acid (18:0) rather than palmitic acid (16:0). Genomic clone delta9-2 (ole2) also encoded a protein of 445 aa which had 86% identity to the delta9-1 and LM9 proteins and whose ORF also complemented the yeast ole1 mutation. The transcript from this gene could only be detected in one of the six M. alpina strains tested, suggesting that its expression may be strain-specific or induced under certain physiological conditions.

Effect of pH on hen egg white lysozyme production and evolution of a recombinant strain of Aspergillus niger

An Aspergillus niger strain (B1) transformed to produce mature hen egg white lysozyme (HEWL) from a glucoamylase fusion protein under control of the A. niger glucoamylase promoter was grown in glucose-limited chemostat culture at a dilution rate of 0.07 h-1 at various pH values. Maximum HEWL production (9.3 mg g-1; specific production rate = 0.65 mg g-1 per h) was obtained at pH 4.5. However, in chemostat culture, HEWL production was not stable at any pH tested. After 240 h in steady state, specific production decreased to only 0.03 +/- 0.01 and 0.24 +/- 0.02 mg g-1 per h at pH 6.5 and 4.5, respectively. Some isolates removed from the chemostat cultures had lost copies of the HEWL gene and when grown in shake flask cultures all of the isolates produced less HEWL than the parental strain. Morphological mutants with similar phenotypes were isolated at all pHs, but their rate of increase in the population was pH dependent, with cultures at low pH (< 4.5) being more morphologically stable than cultures at high (> 4.5) pH. The selective advantage of these mutants was also generally dependent on pH. Both yellow pigment producing mutants and brown sporulation mutants had higher selective advantages over the parental strain at high than at low pH, regardless of the pH at which they were isolated. However, the selective advantage of densely sporulating mutants was independent of pH.

Expression of the VEGF gene family during retinal vaso-obliteration and hypoxia

Vascular insufficiency and retinal ischaemia precede many proliferative retinopathies and stimulate secretion of vasoactive growth factors. Vascular endothelial growth factor (VEGF) plays a major role and we therefore investigated the other members of the VEGF family: Placental growth factor (PlGF), VEGF-B, -C, and -D, and platelet derived growth factors (PDGF) A and B. Neonatal mice were exposed to hyperoxia for 5 days and then returned to room air (resulting in acute retinal ischaemia). RT-PCR demonstrated that all the members of the VEGF family are expressed in the retina and in situ hybridization (ISH) located their mRNAs primarily in ganglion cells. Similarly to VEGF itself, VEGF-C, PDGF-A, and PDGF-B were upregulated during retinal ischaemia (P < 0.05). Only PlGF gene expression increased during hyperoxia (P < 0.01). The expression pattern of these growth factors suggests a role in the normal retina and during vaso-obliterative and ischaemic phases.

Expression, purification, and characterization of the recombinant calcium-binding equine lysozyme secreted by the filamentous fungus Aspergillus niger: comparisons with the production of hen and human lysozymes

Equine lysozyme (EqL) has been expressed from a synthetic gene and secreted from a heterologous host, the filamentous fungus Aspergillus niger. By including 100 mM Ca2+ in the growth medium, secreted yields of more than 50 mg/liter could be achieved using polyvinylpyrrolidone (PVP) complete medium. In a soya medium yields of up to 150 mg/liter were achieved. The production of recombinant human lysozyme (HuL) from A. niger with yields of over 40 mg/liter was also achieved using PVP medium. Addition of Ca2+ to the growth medium reduced the yield of both HuL and hen egg white lysozyme (HEWL). Sequence differences between the three lysozymes, EqL, HuL, and HEWL, resulted in different susceptibilities to cleavage by A. niger proteases. An improved procedure for the purification of EqL and HuL from A. niger allowed separation of the proteins from pigments produced by the fungus. Detailed spectroscopic analysis, including 2D 1H NMR, for recombinant EqL and recombinant HuL confirm that both proteins possess their native structure and are purified to homogeneity.

Plasma levels of endothelin-1 in diabetic retinopathy in pregnancy

PURPOSE

Raised circulating levels of the potent vasoconstrictor endothelin-1 (ET-1) have been demonstrated in diabetes and pregnancy-induced hypertension. Pregnant women with diabetic retinopathy are known to be at a higher risk of developing pregnancy-induced hypertension than those without retinopathy. To examine the association between ET-1, pregnancy, diabetes and diabetic retinopathy, circulating ET-1 levels were measured in each trimester in a cohort of women with and without diabetes during pregnancy.

METHODS

A cohort of women with diabetes (n = 13) and normal controls (n = 8) were followed throughout pregnancy. Detailed clinical and fundoscopic examinations were carried out according to ETDRS protocols. Plasma ET-1 levels were measured in each trimester using a sensitive radioimmunoassay. Those with diabetes were further divided into those with retinopathy (n = 7) and those without (n = 6).

RESULTS

Plasma levels of ET-1 increased progressively during normal pregnancy and peaked in the third trimester. Women with diabetes had significantly higher levels of plasma ET-1 (14.0 vs 4.6 pg/ml in the first trimester, 14.0 vs 4.8 pg/ml in the second trimester and 15.8 vs 7.2 pg/ml in the third trimester) compared with those without diabetes. These were no significant differences in plasma ET-1 levels between women with diabetes who had pre-existing diabetic retinopathy and those without.

CONCLUSION

This study has shown that ET-1 levels rise during normal pregnancy, and are higher in women with diabetes, which may reflect pre-existing endothelial damage. Although no association could be demonstrated between diabetic retinopathy and serum ET-1 levels, this may reflect the small sample size in this study.

Ophthalmic and visual profile of guide dog owners in Scotland

BACKGROUND/AIMS

Out of an estimated 90,000 visually impaired people in Scotland, 509 make use of a guide dog. Initial research in Northern Ireland suggests that the ophthalmic profile of guide dog owners (GDOs) is highly specific. The aim of this study was to compare the ophthalmic and visual characteristics of Scottish GDOs with other groups of visually impaired people.

METHODS

A random sample of GDOs from central and northern Scotland (n = 82) underwent a detailed assessment of residual vision (distance and near acuity, visual fields, contrast, and glare sensitivity). Comparative data were obtained from two populations of visually impaired non-GDOs-one group attending hospital ophthalmic and low vision clinics (n = 50) the other social services rehabilitation clients (n = 35). All participants completed a questionnaire to elicit ophthalmic history, age, and registration details.

RESULTS

GDOs were found to be significantly younger and more profoundly visually impaired than non-GDOs. The main causes of visual impairment were retinitis pigmentosa (23%), optic atrophy (15%), and retinopathy of prematurity (7%). Ninety nine per cent of GDOs were registered blind and had been visually impaired for an average of 39 years. Only 31% were totally blind.

CONCLUSION

GDOs represent a unique minority of the visually impaired population. Epidemiological registration trends would suggest that the numbers of young profoundly visually impaired people are unlikely to increase relative to their elderly counterparts. This has implications on the future demand for guide dog ownership.

Oxidative insult specifically decreases levels of a mitochondrial transcript

The effects of oxidative insult, applied with hydrogen peroxide, on gene transcript levels in a human lymphocyte cell line (Molt-17) were investigated using mRNA differential display. Several cDNA fragments corresponding to putatively up- or down-regulated transcripts were isolated. One of these was found to hybridize to two discrete transcripts on Northern blots of Molt-17 cell RNA. The more abundant transcript, that has previously been demonstrated to correspond to the mRNA for mitochondrial ATPase subunits 8 and 6, was unaffected by the hydrogen peroxide treatment. In contrast, levels of the rarer, larger transcript were consistently reduced in a rapid, sustained, and dose-dependent manner following hydrogen peroxide treatment. Prior supplementation of the cells with beta carotene provided some protection against the reduction in levels of this transcript following hydrogen peroxide treatment. In contrast, vitamins C and E had no effect at the concentrations tested. We have now cloned the cDNA corresponding to this stress-responsive transcript and demonstrated that it is an incompletely processed product of the mitochondrial genome encompassing ATPase subunits 8 and 6 plus the adjacent gene for cytochrome c oxidase subunit 3. This decrease in one specific mitochondrial transcript may represent a novel mechanism for differential expression of mitochondrially-encoded genes.

Homologs of aflatoxin biosynthesis genes and sequence of aflR in Aspergillus oryzae and Aspergillus sojae

The presence, but not expression, of homologs of three structural genes and a regulatory gene necessary for aflatoxin biosynthesis in Aspergillus parasiticus and A. flavus was shown for A. oryzae and A. sojae. Homologs of the regulatory gene aflR were cloned and sequenced from A. oryzae and A. sojae.

Isolation and characterisation of the acetyl-CoA carboxylase gene from Aspergillus nidulans

The putative gene encoding acetyl-CoA carboxylase, accA, has been isolated from Aspergillus nidulans. This single-copy gene has an open reading frame (ORF) of 6864 bp and contains two small introns near the 5'-end. A short ORF upstream of the ATG start codon has been identified in this gene by RT-PCR. Based on sequence homology to acetyl-CoA carboxylases from other organisms, putative biotin-, ATP-, HCO3-- and acetyl-CoA- binding sites have been assigned. Northern data and ACC enzyme-activity measurements from A. nidulans suggested that expression of accA was higher in media containing nitrate than ammonia as a sole nitrogen source. Deletion of accA in A. nidulans was unsuccessful. The failure of A. nidulans to grow in the presence of the ACC-specific inhibitor, soraphen A, supplemented with C16-18 fatty acids suggested that ACC is an essential enzyme.

Advanced glycation end products in vitreous: Structural and functional implications for diabetic vitreopathy

PURPOSE

Advanced glycation end products (AGEs) form irreversible cross-links with many macromolecules and have been shown to accumulate in tissues at an accelerated rate in diabetes. In the present study, AGE formation in vitreous was examined in patients of various ages and in patients with diabetes. Ex vivo investigations were performed on bovine vitreous incubated in glucose to determine AGE formation and cross-linking of vitreous collagen.

METHODS

By means of an AGE-specific enzyme-linked immunosorbent assay (ELISA), AGE formation was investigated in vitreous samples obtained after pars plana vitrectomy in patients with and without diabetes. In addition, vitreous AGEs were investigated in bovine vitreous collagen after incubation in high glucose, high glucose with aminoguanidine, or normal saline for as long as 8 weeks. AGEs and AGE cross-linking was subsequently determined by quantitative and qualitative assays.

RESULTS

There was a significant correlation between AGEs and increasing age in patients without diabetes (r = 0.74). Furthermore, a comparison between age-matched diabetic and nondiabetic vitreous showed a significantly higher level of AGEs in the patients with diabetes (P < 0.005). Collagen purified from bovine vitreous incubated in 0.5 M glucose showed an increase in AGE formation when observed in dot blot analysis, immunogold labeling, and AGE ELISA. Furthermore, there was increased cross-linking of collagen in the glucose-incubated vitreous, when observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and protein separation. This cross-linking was effectively inhibited by coincubation with 10 mM aminoguanidine.

CONCLUSIONS

This study suggests that AGEs may form in vitreous with increasing age. This process seems to be accelerated in the presence of diabetes and as a consequence of exposure to high glucose. Advanced glycation and AGE cross-linking of the vitreous collagen network may help to explain the vitreous abnormalities characteristic of diabetes.

Determinants of the fidelity of processing glucoamylase-lysozyme fusions by Aspergillus niger

Fusion proteins are used to enhance the yields of heterologous proteins secreted from filamentous fungi. In Aspergillus niger, the target protein is normally fused downstream of the carrier protein glucoamylase with a Lys-Arg KEX2-like cleavage site at the junction. This is cleaved in vivo to release mature protein but the processing is not always accurate. We have used N-terminal mutant lysozymes to vary the sequence immediately downstream of the KEX site, and also varied the amino acid sequence upstream of the KEX processing site, to study the fidelity of processing. The sequences both upstream and downstream of the KEX2 site affected the fidelity of cleavage. With some constructs, a range of processing sites were apparent and the relative proportions were time dependent in batch cultures of A. niger. Aberrant processing was related to the secondary-structure preferences of the amino acids in and around the KEX site. Downstream of the processing site, the fidelity of processing decreased in proportion to the tendency for helix formation.