Targeted protein degradation: from small molecules to complex organelles-a Keystone Symposia report

Targeted protein degradation is critical for proper cellular function and development. Protein degradation pathways, such as the ubiquitin proteasomes system, autophagy, and endosome-lysosome pathway, must be tightly regulated to ensure proper elimination of misfolded and aggregated proteins and regulate changing protein levels during cellular differentiation, while ensuring that normal proteins remain unscathed. Protein degradation pathways have also garnered interest as a means to selectively eliminate target proteins that may be difficult to inhibit via other mechanisms. On June 7 and 8, 2021, several experts in protein degradation pathways met virtually for the Keystone eSymposium "Targeting protein degradation: from small molecules to complex organelles." The event brought together researchers working in different protein degradation pathways in an effort to begin to develop a holistic, integrated vision of protein degradation that incorporates all the major pathways to understand how changes in them can lead to disease pathology and, alternatively, how they can be leveraged for novel therapeutics.

Adaptor linked K63 di-ubiquitin activates Nedd4/Rsp5 E3 ligase

Nedd4/Rsp5 family E3 ligases mediate numerous cellular processes, many of which require the E3 ligase to interact with PY motif containing adaptor proteins. Several arrestin-related trafficking adaptors (ARTs) of Rsp5 were self-ubiquitinated for activation, but the regulation mechanism remains elusive. Remarkably, we demonstrate that Art1, Art4, and Art5 undergo K63-linked di-ubiquitination by Rsp5. This modification enhances the plasma membrane recruitment of Rsp5 by Art1 or Art5 upon substrate induction, required for cargo protein ubiquitination. In agreement with these observations, we find that di-ubiquitin strengthens the interaction between the pombe orthologs of Rsp5 and Art1, Pub1, and Any1. Furthermore, we discover that the homologous to E6AP C-terminus (HECT) domain exosite protects the K63-linked di-ubiquitin on the adaptors from cleavage by the deubiquitination enzyme Ubp2. Together, our study uncovers a novel ubiquitination modification implemented by Rsp5 adaptor proteins, underscoring the regulatory mechanism of how adaptor proteins control the recruitment, and activity of Rsp5 for the turnover of membrane proteins.

Golgi membrane protein Erd1 Is essential for recycling a subset of Golgi glycosyltransferases

Protein glycosylation in the Golgi is a sequential process that requires proper distribution of transmembrane glycosyltransferase enzymes in the appropriate Golgi compartments. Some of the cytosolic machinery required for the steady-state localization of some Golgi enzymes are known but existing models do not explain how many of these enzymes are localized. Here, we uncover the role of an integral membrane protein in yeast, Erd1, as a key facilitator of Golgi glycosyltransferase recycling by directly interacting with both the Golgi enzymes and the cytosolic receptor, Vps74. Loss of Erd1 function results in mislocalization of Golgi enzymes to the vacuole/lysosome. We present evidence that Erd1 forms an integral part of the recycling machinery and ensures productive recycling of several early Golgi enzymes. Our work provides new insights on how the localization of Golgi glycosyltransferases is spatially and temporally regulated, and is finely tuned to the cues of Golgi maturation.

Calcineurin-dependent regulation of endocytosis by a plasma membrane ubiquitin ligase adaptor, Rcr1

Rsp5, the Nedd4 family member in yeast, is an E3 ubiquitin ligase involved in numerous cellular processes, many of which require Rsp5 to interact with PY-motif containing adaptor proteins. Here, we show that two paralogous transmembrane Rsp5 adaptors, Rcr1 and Rcr2, are sorted to distinct cellular locations: Rcr1 is a plasma membrane (PM) protein, whereas Rcr2 is sorted to the vacuole. Rcr2 is delivered to the vacuole using ubiquitin as a sorting signal. Rcr1 is delivered to the PM by the exomer complex using a newly uncovered PM sorting motif. Further, we show that Rcr1, but not Rcr2, is up-regulated via the calcineurin/Crz1 signaling pathway. Upon exogenous calcium treatment, Rcr1 ubiquitinates and down-regulates the chitin synthase Chs3. We propose that the PM-anchored Rsp5/Rcr1 ubiquitin ligase-adaptor complex can provide an acute response to degrade unwanted proteins under stress conditions, thereby maintaining cell integrity.

Membrane Protein Quality Control Mechanisms in the Endo-Lysosome System

Protein quality control (PQC) machineries play a critical role in selective identification and removal of mistargeted, misfolded, and aberrant proteins. This task is extremely complicated due to the enormous diversity of the proteome. It also requires nuanced and careful differentiation between 'normal' and 'folding intermediates' from 'abnormal' and 'misfolded' protein states. Multiple genetic and proteomic approaches have started to delineate the molecular underpinnings of how these machineries recognize their target and how their activity is regulated. In this review, we summarize our understanding of the various E3 ubiquitin ligases and associated machinery that mediate PQC in the endo-lysosome system in yeast and humans, how they are regulated, and mechanisms of target selection, with the intent of guiding future research in this area.

A multicentre observational study on the epidemiology, risk factors, management and outcomes of mucormycosis in India

OBJECTIVES

To describe the epidemiology, management and outcome of individuals with mucormycosis; and to evaluate the risk factors associated with mortality.

METHODS

We conducted a prospective observational study involving consecutive individuals with proven mucormycosis across 12 centres from India. The demographic profile, microbiology, predisposing factors, management and 90-day mortality were recorded; risk factors for mortality were analysed.

RESULTS

We included 465 patients. Rhino-orbital mucormycosis was the most common (315/465, 67.7%) presentation followed by pulmonary (62/465, 13.3%), cutaneous (49/465, 10.5%), and others. The predisposing factors included diabetes mellitus (342/465, 73.5%), malignancy (42/465, 9.0%), transplant (36/465, 7.7%), and others. Rhizopus species (231/290, 79.7%) were the most common followed by Apophysomyces variabilis (23/290, 7.9%), and several rare Mucorales. Surgical treatment was performed in 62.2% (289/465) of the participants. Amphotericin B was the primary therapy in 81.9% (381/465), and posaconazole was used as combination therapy in 53 (11.4%) individuals. Antifungal therapy was inappropriate in 7.6% (30/394) of the individuals. The 90-day mortality rate was 52% (242/465). On multivariate analysis, disseminated and rhino-orbital (with cerebral extension) mucormycosis, shorter duration of symptoms, shorter duration of antifungal therapy, and treatment with amphotericin B deoxycholate (versus liposomal) were independent risk factors of mortality. A combined medical and surgical management was associated with a better survival.

CONCLUSIONS

Diabetes mellitus was the dominant predisposing factor in all forms of mucormycosis. Combined surgical and medical management was associated with better outcomes. Several gaps surfaced in the management of mucormycosis. The rarer Mucorales identified in the study warrant further evaluation.

Methods for studying the regulation of membrane traffic by ubiquitin and the ESCRT pathway

Covalent modification of proteins with ubiquitin dynamically regulates their function and fate. The ubiquitination of most plasma membrane proteins initiates endocytosis and ESCRT-mediated sorting to the lysosomal lumen for degradation. Powerful genetic approaches in the budding yeast Saccharomyces cerevisiae have been particularly instrumental in the discovery and elucidation of these molecular mechanisms, which are conserved in all eukaryotes. Here we provide two detailed protocols and tools for studying ubiquitination-dependent membrane trafficking mechanisms in yeast. The first utilizes fusions between a protein of interest and an auxotrophic marker to screen for mutants that affect ubiquitin-mediated endocytosis. The second method artificially ubiquitinates a protein of interest, allowing downstream trafficking steps to be studied independently from the regulatory signals that initiate endocytosis.

Rsp5 Ubiquitin ligase-mediated quality control system clears membrane proteins mistargeted to the vacuole membrane

Sardana et al. show that protein quality control systems on multiple endocytic organelles cooperate to prevent aberrant protein accumulation and maintain proteostasis. By mistargeting PM proteins de novo to the yeast vacuolar membrane, they uncover a “fail-safe” mechanism that ensures degradation of diverse endocytic cargos.

Maintenance of organelle identity is profoundly dependent on the coordination between correct targeting of proteins and removal of mistargeted and damaged proteins. This task is mediated by organelle-specific protein quality control (QC) systems. In yeast, the endocytosis and QC of most plasma membrane (PM) proteins requires the Rsp5 ubiquitin ligase and ART adaptor network. We show that intracellular adaptors of Rsp5, Ear1, and Ssh4 mediate recognition and vacuolar degradation of PM proteins that escape or bypass PM QC systems. This second tier of surveillance helps to maintain cell integrity upon heat stress and protects from proteotoxicity. To understand the mechanism of the recognition of aberrant PM cargos by Ssh4–Rsp5, we mistarget multiple PM proteins de novo to the vacuolar membrane. We found that Ssh4–Rsp5 can target and ubiquitinate multiple lysines within a restricted distance from the membrane, providing a fail-safe mechanism for a diverse cargo repertoire. The mistargeting or misfolding of PM proteins likely exposes these lysines or shifts them into the “ubiquitination zone” accessible to the Ssh4–Rsp5 complex.

Actinobacillus ureae: an unusual cause of tree-in-bud pattern in a case of pneumonia on lung computed tomographic scan-first clinical case report and review of the literature from India

A 62-year-old man with asthma sought care for intermittent fever, cough with expectoration, breathlessness and orthopnoea with grunting. Computed tomography revealed clusters of centrilobular nodules on both sides with a tree-in-bud appearance and mild diffuse bronchial wall thickening. Sputum sample grew pure colonies of Actinobacillus ureae which was confirmed by MALDI-TOF and 16SrRNA gene sequencing. A. ureae may be an additional bacteriologic causative agent of the tree-in-bud pattern on computed tomographic scan.

Escherichia vulneris: an unusual cause of complicated diarrhoea and sepsis in an infant. A case report and review of literature

Escherichia vulneris is an opportunistic human pathogen. It has been primarily reported in adult patients and invasive infections have been observed in immune-suppressed individuals. This is the first report of E. vulneris causing complicated diarrhoea and sepsis in an infant.

Two month old sick infant, born full-term, was admitted to the paediatrics department with loose motions and refusal to feed for four days. E. vulneris was isolated from blood in pure culture. The isolate was characterized for diarrhoeal virulence markers: heat labile and heat stable toxins (LT, ST) and hemolysin (hlyA) by PCR. The presence of LT enterotoxin and hemolysin provides strong evidence of the diarrhoeagenic potential of E. vulneris, further leading to the invasive infection triggering sepsis.

As E. vulneris can lead to serious complications, an attempt should be made in clinical laboratories to identify and further characterize this new Escherichia species.

Linezolid-resistant mucoid Staphylococcus haemolyticus from a tertiary-care centre in Delhi

We report an unusual morphological mucoid variant of Staphylococcus haemolyticus associated with linezolid resistance from a patient with sepsis. Linezolid resistance and mucoid character together made this pathogen difficult to treat. To our knowledge this is the first such report.

The rRNA methyltransferase Bud23 shows functional interaction with components of the SSU processome and RNase MRP

Bud23 is responsible for the conserved methylation of G1575 of 18S rRNA, in the P-site of the small subunit of the ribosome. bud23Δ mutants have severely reduced small subunit levels and show a general failure in cleavage at site A2 during rRNA processing. Site A2 is the primary cleavage site for separating the precursors of 18S and 25S rRNAs. Here, we have taken a genetic approach to identify the functional environment of BUD23. We found mutations in UTP2 and UTP14, encoding components of the SSU processome, as spontaneous suppressors of a bud23Δ mutant. The suppressors improved growth and subunit balance and restored cleavage at site A2. In a directed screen of 50 ribosomal trans-acting factors, we identified strong positive and negative genetic interactions with components of the SSU processome and strong negative interactions with components of RNase MRP. RNase MRP is responsible for cleavage at site A3 in pre-rRNA, an alternative cleavage site for separating the precursor rRNAs. The strong negative genetic interaction between RNase MRP mutants and bud23Δ is likely due to the combined defects in cleavage at A2 and A3. Our results suggest that Bud23 plays a role at the time of A2 cleavage, earlier than previously thought. The genetic interaction with the SSU processome suggests that Bud23 could be involved in triggering disassembly of the SSU processome, or of particular subcomplexes of the processome.

Las1 interacts with Grc3 polynucleotide kinase and is required for ribosome synthesis in Saccharomyces cerevisiae

Ribosome biogenesis is a multi-step process that couples cell growth with cell proliferation. Although several large-scale analysis of pre-ribosomal particles have identified numerous trans-acting factors involved in this process, many proteins involved in pre-rRNA processing and ribosomal subunit maturation have yet to be identified. Las1 was originally identified in Saccharomyces cerevisiae as a protein involved in cell morphogenesis. We previously demonstrated that the human homolog, Las1L, is required for efficient ITS2 rRNA processing and synthesis of the 60S ribosomal subunit. Here, we report that the functions of Las1 in ribosome biogenesis are also conserved in S. cerevisiae. Depletion of Las1 led to the accumulation of both the 27S and 7S rRNA intermediates and impaired the synthesis of the 60S subunit. We show that Las1 co-precipitates mainly with the 27S rRNA and associates with an Nsa1 and Rix1-containing pre-60S particle. We further identify Grc3 as a major Las1-interacting protein. We demonstrate that the kinase activity of Grc3 is required for efficient pre-rRNA processing and that depletion of Grc3 leads to rRNA processing defects similar to the ones observed in Las1-depleted cells. We propose that Las1 and Grc3 function together in a conserved mechanism to modulate rRNA processing and eukaryotic ribosome biogenesis.

The methyltransferase adaptor protein Trm112 is involved in biogenesis of both ribosomal subunits

We previously identified Bud23 as the methyltransferase that methylates G1575 of rRNA in the P-site of the small (40S) ribosomal subunit. In this paper, we show that Bud23 requires the methyltransferase adaptor protein Trm112 for stability in vivo. Deletion of Trm112 results in a bud23Δ-like mutant phenotype. Thus Trm112 is required for efficient small-subunit biogenesis. Genetic analysis suggests the slow growth of a trm112Δ mutant is due primarily to the loss of Bud23. Surprisingly, suppression of the bud23Δ-dependent 40S defect revealed a large (60S) biogenesis defect in a trm112Δ mutant. Using sucrose gradient sedimentation analysis and coimmunoprecipitation, we show that Trm112 is also involved in 60S subunit biogenesis. The 60S defect may be dependent on Nop2 and Rcm1, two additional Trm112 interactors that we identify. Our work extends the known range of Trm112 function from modification of tRNAs and translation factors to both ribosomal subunits, showing that its effects span all aspects of the translation machinery. Although Trm112 is required for Bud23 stability, our results suggest that Trm112 is not maintained in a stable complex with Bud23. We suggest that Trm112 stabilizes its free methyltransferase partners not engaged with substrate and/or helps to deliver its methyltransferase partners to their substrates.

5' and 3' end modifications of spliceosomal RNAs in Plasmodium falciparum

5' caps provide recognition sequences for the nuclear import of snRNAs. The 5' and 3' ends of snRNAs were studied in Plasmodium falciparum with a modified adapter ligation method, which showed that 5' ends of U1, U2, U4, U5 and U6 snRNAs are capped. In P. falciparum, the 3' ends of U1, U2, U4 and U5 snRNAs have free hydroxyl groups whereas U6 snRNA has a blocked 3' end. An immunoprecipitation assay for trimethyl guanosine caps shows that the cap structures of parasite U1-U5 snRNAs are hypermethylated while U6 snRNA may be gamma-mono-methylated. Bioinformatics analysis of proteins involved in hypermethylation and trafficking of snRNAs indicates that the methyltransferase TGS1 is present in the P. falciparum genome. PfTGS1 is larger than its orthologs and may have transmembrane domains in the C-terminus. Surprisingly, the snRNA trafficking protein Snurportin is absent from the P. falciparum genome suggesting that reminiscent of yeast, parasite snRNAs may be retained in the nucleus.

Catheter ablation of left free wall accessory pathway in a patient with inferior vena cava interruption

Access to the right side of the heart for diagnostic and interventional procedures is usually obtained via the femoral vein and inferior vena cava. Anatomic variations or obstruction of the inferior vena cava can make this access difficult. In such cases, alternative routes to the right side of the heart such as the azygos vein and the superior vena cava can be used.

Inheritance and expression of the cry1Ab gene in Bt ( Bacillus thuringiensis) transgenic rice

The inheritance and expression patterns of the cry1Ab gene were studied in the progenies derived from different Bt ( Bacillus thuringiensis) transgenic japonica rice lines under field conditions. Both Mendelian and distorted segregation ratios were observed in some selfed and crossed F(2) populations. Crosses between japonica intra-subspecies had no significant effect on the segregation ratios of the cry1Ab gene, but crossing between japonica and indicainter-subspecies led to distorted segregation of the cry1Ab gene in the F(2)population. Field-release experiments indicated that the cry1Ab gene was stably transmitted in an intact manner via successive sexual generations, and the concentration of the Cry1Ab protein was kept quantitatively stable up to the R(6)generation. The cry1Ab gene, driven by the maize ubiquitinpromoter, displayed certain kinds of spatial and temporal expression patterns under field conditions. The content of the Cry1Ab protein varied in different tissues of the main stems, the primary tillers and the secondary tillers. Higher levels of the Cry1Ab protein were found in the stems, leaves and leaf sheaths than in the roots, while the lowest level was detected in grains at the maturation stage. The content of the Cry1Ab protein in the leaves peaked at the booting stage and was lowest at the heading stage. Furthermore, the Cry1Ab content of cry1Ab expression in different tissues of transgenic rice varied individually with temperature.

Sorting of glycoprotein B from human cytomegalovirus to protein storage vesicles in seeds of transgenic tobacco

As part of ongoing studies into the use of plant expression systems for making human therapeutic proteins, we have successfully expressed the major glycoprotein, gB, of human cytomegalovirus (HCMV) in transgenic tobacco plants. Viral glycoprotein was detectable in the protein extracts of mature tobacco seeds using neutralizing and non-neutralizing monoclonal antibodies specific for gB. Although several mammalian proteins have been expressed in tobacco, localization of these proteins in transgenic tobacco tissue has not been extensively examined. The objective of this study was to identify the site(s) of recombinant gB deposition in mature tobacco seeds. Using immunogold labelling and electron microscopy, we found specific labelling for gB in the endosperm of transgenic seeds, with gB localized almost exclusively in protein storage vesicles (PSV). This occurred in seeds that were freshly harvested and in seeds that had been stored for several months. These data indicate that gB behaves like a plant storage protein when expressed in tobacco seeds, and provide further support for the suitability of plants for producing recombinant proteins of potential clinical relevance.

Development of biopharmaceuticals in plant expression systems: cloning, expression and immunological reactivity of human cytomegalovirus glycoprotein B (UL55) in seeds of transgenic tobacco

Plant seeds offer unique opportunities for the production and delivery of oral subunit vaccines. We have used the immunodominant glycoprotein B complex of human cytomegalovirus (HCMV), introduced into tobacco plants, as a model system for studying the merit of this promising approach. Given the advantages of expressing proteins in seeds, a novel expression vector was developed incorporating regulatory sequences of glutelin, the major rice seed storage protein, to direct synthesis of recombinant glycoprotein B. Analysis of genomic DNA of 28 selected tobacco transformants by PCR amplification showed that 71% harboured the gB cDNA, a finding further documented by Southern blotting. Specific immunoassays of protein extracts from seeds of positive plants showed that all were producing antigenic glycoprotein B at levels ranging from 70-146 ng/mg extracted protein. In addition, similarity with native glycoprotein B produced in HCMV-infected cells was also demonstrated by inhibition of immunofluorescence on HCMV-infected human fibroblasts. These data are the first to report the expression of an immunodominant antigen of HCMV in plant tissues, indicating the fidelity with which this very large heterologous viral glycoprotein can be synthesized in this model system.

Agrobacterium-transformed rice plants expressing synthetic cryIA(b) and cryIA(c) genes are highly toxic to striped stem borer and yellow stem borer

Over 2,600 transgenic rice plants in nine strains were regenerated from >500 independently selected hygromycin-resistant calli after Agrobacterium-mediated transformation. The plants were transformed with fully modified (plant codon optimized) versions of two synthetic cryIA(b) and cryIA(c) coding sequences from Bacillus thuringiensis as well as the hph and gus genes, coding for hygromycin phosphotransferase and beta-glucuronidase, respectively. These sequences were placed under control of the maize ubiquitin promoter, the CaMV35S promoter, and the Brassica Bp10 gene promoter to achieve high and tissue-specific expression of the lepidopteran-specific delta-endotoxins. The integration, expression, and inheritance of these genes were demonstrated in R0 and R1 generations by Southern, Northern, and Western analyses and by other techniques. Accumulation of high levels (up to 3% of soluble proteins) of CryIA(b) and CryIA(c) proteins was detected in R0 plants. Bioassays with R1 transgenic plants indicated that the transgenic plants were highly toxic to two major rice insect pests, striped stem borer (Chilo suppressalis) and yellow stem borer (Scirpophaga incertulas), with mortalities of 97-100% within 5 days after infestation, thus offering a potential for effective insect resistance in transgenic rice plants.

Construction and rapid testing of synthetic and modified toxin gene sequences CryIA (b&c) by expression in maize endosperm culture

The synthesis of two modified genes, Cry IA(b) and CryIA(c), each consisting of 1845 bp, is described in detail. The genes were synthesized using an improved PCR procedure based on recursive principles. The synthetic CryIA(c) gene was put under the control of a maize ubiquitin promoter. This construct was tested in a maize endosperm-derived suspension culture system. The use of maize endosperm culture as a quick and efficient system to test the activity of synthetic genes is described.

Correlation between the size of the intergenic regulatory region, the status of cytosine methylation of rRNA genes and nucleolar expression in wheat

A large number of wheat rRNA genes are methylated at all the CCGG sites that are present in the intergenic regions. A smaller number of rRNA genes are not methylated at one or more CCGG sites. A subset of genes was found unmethylated at a specific CCGG site just downstream of the array of 135 bp A repeats in the intergenic region. In all the genotypes studied, the rDNA loci with larger intergenic regions between their genes also possess a greater number of rRNA genes that are unmethylated at one or more CCGG sites in the intergenic regions than do the loci with shorter intergenic regions. In four genotypes (for which data were available), rDNA loci with longer intergenic regions had larger secondary constrictions on metaphase chromosomes, a measure of relative locus activity, than the loci with shorter intergenic regions. The results have been integrated into a model for the control of rDNA expression based on correlations between cytosine methylation patterns and the number of upstream 135 bp repeats in intergenic regions. According to this model the 135 bp repeats play a part in the control of gene activity by binding a protein(s) that is in limiting supply, thereby predisposing the neighbouring gene to become active preferentially.

Nutritional management of osteoporosis. To slow the advancement of osteoporosis, nurses must encourage their clients to increase their intake of calcium. For geriatric nurses, this may be a challenge

In conclusion, no current effective therapy is available for the restoration of bone mass once osteoporosis has developed. Primary prevention is the best way to fight this problem. However, goals for the management of osteoporosis are (1) to maintain skeletal mass and integrity, (2) to slow bone resorption, and (3) to treat the symptomatic problem and its sequelae. Having a well-balanced diet containing adequate amounts of calcium, use of calcium supplements when necessary, reducing risk factors in life-style, and use of estrogen are therapeutic measures to reduce bone loss. Clients are also encouraged to exercise by walking or swimming and remain as active as possible. It is important to avoid strain on the spine, as occurs in lifting or bending, to prevent compression fractures on the vertebrae. For treating the symptoms of osteoporosis and its sequelae, it is necessary to relieve pain (by the use of analgesics), provide comfortable light mechanical support for the spine, if needed, arrange assistance in activities of daily living, coordinate a rehabilitation program, and provide emotional support and reassurance to the patient and family. This may be an area largely neglected in practice. Gerontologic nurses may be the first to take the time to thoroughly discuss osteoporosis with their elderly clients and help them to develop a comprehensive program. If through their efforts some falls and fractures can be prevented, this is nursing at its best.

A Brassica napus gene family which shows sequence similarity to ascorbate oxidase is expressed in developing pollen. Molecular characterization and analysis of promoter activity in transgenic tobacco plants

The genomic clone named Bp10 contains a member of a small pollen-specific gene family of B. napus. The expression of the Bp10 gene family is maximal in early binucleate microspores and declines considerably in mature trinucleate pollen. Homologues of the Bp10 genes are expressed in the pollen of other plant species. The pollen-specific expression of the gene contained in the genomic clone was confirmed in tobacco plants transformed with a chimeric Bp10 promoter/GUS construct. A promoter fragment of 396 bp is sufficient to direct a strong and correct spatial and temporal expression in transgenic plants. The Bp10 gene family codes for proteins of 62 kDa showing approximately 30% sequence identify to cucumber and pumpkin ascorbate oxidases (AAOs). However, the AAO active centres are not conserved in the Bp10 products, suggesting an evolutionary relationship but a different enzymatic activity for these proteins. Expression of a recombinant Bp10 protein in E. coli inhibits bacterial growth on minimal medium, suggesting the production of an enzymatically active polypeptide in bacteria. No AAO activity could be correlated with the expression of the recombinant protein. Moreover, substances affecting AAO activity do not appear to influence the inhibitory activity of the protein produced in bacteria. However, as indicated by the rescue of bacterial growth in the presence of sodium bicarbonate or gaseous CO2, the Bp10 protein activity could be modulated by CO2 levels.