Properties, structure, and applications of microbial sterol esterases

Seasonal Dynamics of Culturable Yeasts in Ornithogenically Influenced Soils in a Temperate Forest and Evaluation of Extracellular Enzyme Secretion in Tausonia pullulans at Different Temperatures

The culturable yeast communities in temperate forest soils under the ornithogenic influence were studied in a seasonal dynamic. To investigate the intense ornithogenic influence, conventional and "live" feeders were used, which were attached to trees in the forest and constantly replenished throughout the year. It was found that the yeast abundance in the soil under strong ornithogenic influence reached the highest values in winter compared to the other seasons and amounted to 4.8 lg (cfu/g). This was almost an order of magnitude higher than the minimum value of yeast abundance in ornithogenic soils determined for summer. A total of 44 yeast species, 21 ascomycetes and 23 basidiomycetes, were detected in ornithogenic soil samples during the year. These included soil-related species (Barnettozyma californica, Cyberlindnera misumaiensis, Cutaneotrichosporon moniliiforme, Goffeauzyma gastrica, Holtermanniella festucosa, Leucosporidium creatinivorum, L. yakuticum, Naganishia adeliensis, N. albidosimilis, N. globosa, Tausonia pullulans, and Vanrija albida), eurybionts (yeast-like fungus Aureobasidium pullulans, Debaryomyces hansenii, and Rhodotorula mucilaginosa), inhabitants of plant substrates and litter (Cystofilobasidium capitatum, Cys. infirmominiatum, Cys. macerans, Filobasidium magnum, Hanseniaspora uvarum, Metschnikowia pulcherrima, and Rh. babjevae) as well as a group of pathogenic and opportunistic yeast species (Arxiozyma bovina, Candida albicans, C. parapsilosis, C. tropicalis, Clavispora lusitaniae, and Nakaseomyces glabratus). Under an ornithogenic influence, the diversity of soil yeasts was higher compared to the control, confirming the uneven distribution of yeasts in temperate forest soils and their dependence on natural hosts and vectors. Interestingly, the absolute dominant species in ornithogenic soils in winter (when the topsoil temperature was below zero) was the basidiomycetous psychrotolerant yeast T. pullulans. It is regularly observed in various soils in different geographical regions. Screening of the hydrolytic activity of 50 strains of this species at different temperatures (2, 4, 10, 15 and 20 °C) showed that the activity of esterases, lipases and proteases was significantly higher at the cultivation temperature. Ornithogenic soils could be a source for the relatively easy isolation of a large number of strains of the psychrotolerant yeast T. pullulans to test, study and optimize their potential for the production of cold-adapted enzymes for industry.

Bioactive Steroids Bearing Oxirane Ring

This review explores the biological activity and structural diversity of steroids and related isoprenoid lipids, with a particular focus on compounds containing an oxirane ring. These natural compounds are derived from fungi, fungal endophytes, as well as extracts of plants, algae, and marine invertebrates. To evaluate their biological activity, an extensive examination of refereed literature sources was conducted, including in vivo and in vitro studies and the utilization of the QSAR method. Notable properties observed among these compounds include strong anti-inflammatory, antineoplastic, antiproliferative, anti-hypercholesterolemic, antiparkinsonian, diuretic, anti-eczematic, anti-psoriatic, and various other activities. Throughout this review, 3D graphs illustrating the activity of individual steroids are presented, accompanied by images of selected terrestrial or marine organisms. Furthermore, this review provides explanations for specific types of biological activity associated with these compounds. The data presented in this review are of scientific interest to the academic community and carry practical implications in the fields of pharmacology and medicine. By analyzing the biological activity and structural diversity of steroids and related isoprenoid lipids, this review offers valuable insights that contribute to both theoretical understanding and applied research. This review draws upon data from various authors to compile information on the biological activity of natural steroids containing an oxirane ring.

Investigation of amino acids related to Staphylococcus saprophyticus AG1 EstAG1 carboxylesterase catalytic function revealed a new family of bacterial lipolytic enzymes

Most of the lipolytic enzymes (carboxylesterases, EC 3.1.1.1 and triacylglycerol acylhydrolases, EC 3.1.1.3) originate from bacteria and form a large group of functionally important enzymes that are also well known for their use in multiple biotechnology sectors. Rapid and increasing amount of bacterial lipolytic enzymes being discovered and characterized led to a necessity to classify them. More than twenty years ago bacterial lipolytic enzymes were originally classified into eight families and six true lipase sub-families based on the differences in their amino acid sequences and biochemical properties. Later, this classification was comprehensively updated to 19 families with eight subfamilies, and more recently, employing deeper comparative analysis methods, classification expanded to 35 families and 11 subfamilies. Bacterial lipolytic enzymes that cannot be classified into currently existing families are still being discovered. This work provides site-directed mutagenesis and differential scanning fluorimetry based investigation of catalytic function-related amino acids of previously discovered and characterized EstAG1 carboxylesterase from Staphylococcus saprophyticus AG1. Experimental results obtained in this work revealed that EstAG1 carboxylesterase can be placed into a new family of bacterial lipolytic enzymes.

Disruption of SMC-related genes promotes recombinant cholesterol esterase production in Burkholderia stabilis

Burkholderia stabilis strain FERMP-21014 secretes cholesterol esterase (BsChe), which is used in clinical settings to determine serum cholesterol levels. Previously, we constructed an expression plasmid with an endogenous constitutive promoter to enable the production of recombinant BsChe. In this study, we obtained one mutant strain with 13.1-fold higher BsChe activity than the wild type, using N-methyl-N'-nitro-N-nitrosoguanidine as a mutagen. DNA-sequencing analysis revealed that the strain had lost chromosome 3 (∆Chr3), suggesting that the genes hindering BsChe production may be encoded on Chr3. We also identified common mutations in the functionally unknown BSFP_068720/30 genes in the top 10 active strains generated during transposon mutagenesis. As BSFP_068720/30/40 comprised an operon on Chr3, we created the BSFP_068720/30/40 disruption mutant and confirmed that each disruption mutant containing the expression plasmid exhibited ~ 16.1-fold higher BsChe activity than the wild type. Quantitative PCR showed that each disruption mutant and ΔChr3 had a ~ 9.4-fold higher plasmid copy number than the wild type. Structural prediction models indicate that BSFP_068730/40 is structurally homologous to the structural maintenance of chromosomes (SMC) protein MukBE, which is responsible for chromosome segregation during cell division. Conversely, BSFP_068720/30/40 disruption did not lead to a Chr3 drop-out. These results imply that BSFP_068720/30/40 is not a SMC protein but is involved in destabilizing foreign plasmids to prevent the influx of genetic information from the environment. In conclusion, the disruption of BSFP_068720/30/40 improved plasmid stability and copy number, resulting in exceptionally high BsChe production. KEY POINTS: • Disruption of BSFP_068720/30/40 enabled mass production of Burkholderia Che/Lip. • BSFP_068730/40 is an SMC protein homolog not involved in chromosome retention. • BSFP_068720/30/40 is likely responsible for the exclusion of exogenous plasmids.

Bioconversion of Phytosterols to 9-Hydroxy-3-Oxo-4,17-Pregadiene-20-Carboxylic Acid Methyl Ester by Enoyl-CoA Deficiency and Modifying Multiple Genes in Mycolicibacterium neoaurum

C22 steroids are valuable precursors for steroid drug synthesis, but the development of C22 steroids remains unsatisfactory. This study presented a strategy for the one-step bioconversion of phytosterols to a C22 steroid drug precursor, 9-hydroxy-3-oxo-4,17-pregadiene-20-carboxylic acid methyl ester (9-OH-PDCE), by 3-ketosteroid-Δ 1 -dehydrogenase and enoyl-CoA hydratase deficiency with overexpression of 17β-hydroxysteroid dehydrogenase acyl-CoA dehydrogenase in Mycolicibacterium .

Ancestral sequence reconstruction as a tool to study the evolution of wood decaying fungi

The study of evolution is limited by the techniques available to do so. Aside from the use of the fossil record, molecular phylogenetics can provide a detailed characterization of evolutionary histories using genes, genomes and proteins. However, these tools provide scarce biochemical information of the organisms and systems of interest and are therefore very limited when they come to explain protein evolution. In the past decade, this limitation has been overcome by the development of ancestral sequence reconstruction (ASR) methods. ASR allows the subsequent resurrection in the laboratory of inferred proteins from now extinct organisms, becoming an outstanding tool to study enzyme evolution. Here we review the recent advances in ASR methods and their application to study fungal evolution, with special focus on wood-decay fungi as essential organisms in the global carbon cycling.

Divergent substrate specificities and regioselectivities of three lipase isoforms from Cordyceps militaris: Combinatorial advantages for entomopathogenicity and prospects as biocatalysts

Cordyceps militaris, an entomopathogenic Cordyceps mushroom, is a crucial ethnopharmacological agricultural product with applications in traditional oriental remedies in East Asia. Since lipases are reported to serve as key enzymatic equipment for entomopathogenic fungi during the host infection, the presence of various lipases with different biochemical features in C. militaris was elucidated. Three lipases from C. militaris (CML) of 60-70 kDa were isolated according to protein hydrophobicity; isoform relationships were identified by peptide mapping using liquid chromatography-electrospray ionization-tandem mass spectrometry. The CML isoforms exhibited distinct substrate specificities, which were related to the hydrophobicity of each isoform. Furthermore, the integral stereoselectivity of each lipase towards trioleoylglycerol diverged into two classes (sn-1,3 and sn-2 regioselectivity) that are rare in canonical fungal lipases. Overall, our results demonstrate that C. militaris secretes lipase isoforms with cocktail-like enzyme functions that may contribute to the entomopathogenic life cycle of C. militaris. Each CML isoform has distinct advantages for biocatalyst applications in the food and oleochemical industries.

Probing the interaction of superparamagnetic iron oxide nanoparticles with lipase and their interacting consequences at the molecular level

Background

Although superparamagnetic iron oxide nanoparticles (SPIONs) are used as carriers for candida rugosa lipase (CRL) in biomedical fields, their interactions and the influences on CRL are still unknown. Consequently, SPIONs were synthesized, characterized, and incubated with CRL to explore their molecular interactions and interacting consequences in this study.

Methods

The toxic effects of SPIONs on CRL and their molecular interactions were explored through transmission electron microscope, isothermal titration calorimetry, zeta potential measurements, multi-spectroscopic techniques, and biological enzyme activity tests.

Results

Results revealed the adsorption of SPIONs to CRL and the reduction of CRL aggregation. The unfolding and loosening of CRL structure as well as the change of secondary structure with the decrease of α-helix were found under SPIONs exposure. Moreover, higher SPIONs concentrations contributed to larger conformational changes and less aggregation of CRL. Meanwhile, it showed that hydrophobic forces were the dominant driving forces in the binding process, with the participation of electrostatic forces. CRL binds to SPIONs with the stoichiometry of 20.7 and the binding constant of 9.9 × 106 M−1. No obvious changes were found in CRL activity due to no interference to Ser-209, Glu-341, and His-449 residues.

Conclusion

This study examined the biological compatibility of SPIONs at the molecular level and provided important information about the structure and function of CRL upon binding to SPIONs. Our work might contribute to comprehend the molecular toxicity of SPIONs and the risks of engineered nanoparticles to human health.

Versatile Lipases from the Candida rugosa-like Family: A Mechanistic Insight Using Computational Approaches

Lipases are enzymes able to catalyze the hydrolysis or synthesis of triglycerides, depending on the reaction conditions, whereas sterol esterases show the same ability on sterol esters. Structurally, both kinds of enzymes display an α/β-hydrolase fold, with a substrate-binding pocket formed by a hydrophobic cavity covered by a mobile lid. However, it has been reported that some lipases from the Candida rugosa-like family display wide substrate specificity on both triglycerides and sterol esters. Among them, enzymes with different biotechnological applications, such as the lipase isoenzymes produced by C. rugosa and the sterol esterase from Ophiostoma piceae, have been exhaustively characterized and their crystal structures are available. Differences in substrate affinity among these proteins have been attributed to changes in their hydrophobicity. In this work, we analyzed the full catalytic mechanisms of these proteins using molecular dynamics tools, gaining insight into their mechanistic properties. In addition, we developed an in silico protocol to predict the substrate specificity using C. rugosa and O. piceae lipases as model enzymes and triglycerides and cholesterol esters with different fatty acid chain lengths as model substrates. The protocol was validated by comparing the in silico results with those described in the literature. These results would be useful to perform virtual screening of substrates for enzymes of the C. rugosa-like family with unknown catalytic properties.

Bacterial triacylglycerol lipase is a potential cholesterol esterase: Identification of a key determinant for sterol-binding specificity

Cholesterol esterase (Che) from Burkholderia stabilis (BsChe) is a homolog of well-characterized and industrially relevant bacterial triacylglycerol lipases (Lips). BsChe is a rare bacterial Lip enzyme that exhibits practical Che activity and is currently used in clinical applications to determine total serum cholesterol levels. To investigate the sterol specificity of BsChe, we determined the X-ray structure of BsChe. We discovered a local structural change in the active-site cleft, which might be related to substrate binding and product release. We also performed molecular docking studies by using the X-ray models of BsChe and cholesterol linoleate (CLL), the most favorable substrate for BsChe. The results showed that the sterol moieties of reasonable CLL docking poses localized to a specific active-site cleft surface formed by Leu266 and Ile287, which are unconserved among Burkholderia Lip homologs. Site-directed mutagenesis identified these residues as essential for the Che activity of BsChe, and Leu or Ile substitution conferred marked Che activity to Burkholderia Lips. In particular, Burkholderia cepacia and Burkholderia ubonensis Lips with the V266L/L287I double mutation exhibited ~50-fold and 500-fold higher Che activities than those of the wild-type enzymes, respectively. These results provide new insights into the substrate-binding mechanisms and selectivities of bacterial Lips.

Biochemical Characterization of a Lipolytic Enzyme From Aspergillus oryzae That Hydrolyzes Triacylglycerol and Sterol Esters

A novel lipolytic enzyme-encoding gene, lipO745, from Aspergillus oryzae RIB40 was cloned and expressed in Pichia pastoris. Purified recombinant LipO745 (rLipO745) had a molecular mass of approximately 60 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. rLipO745 exhibited maximum activity at 40 °C and pH 7.0 and was stable at temperatures ≤ 40 °C. The substrate specificity of purified rLipO745 was analyzed using α-naphthyl esters as artificial substrates and various triacylglycerol and sterol esters as natural substrates. From among a panel of α-naphthyl esters (C2-C16), α-naphthyl butyrate (C4), with an activity of 269 ± 3.3 units/mg protein, was the optimal substrate for hydrolysis by the purified recombinant protein. The K_m and k_cat values of rLiO745 for the C4 substrate were 0.073 ± 0.0012 mM and 608 ± 108 s^-1, respectively. The purified recombinant enzyme had considerable hydrolytic activity toward tributyrin, tripalmitin, and triolein, indicating lipase activity, and toward cholesteryl acetate, butyrate, palmitate, and oleate, indicating sterol esterase activity. Transesterification activities between tributyrin and cholesterol or between tributyrin and campesterol were also determined.

Production of recombinant extracellular cholesterol esterase using consistently active promoters in Burkholderia stabilis

Burkholderia stabilis FERMP-21014 produces highly active cholesterol esterase in the presence of fatty acids. To develop an overexpression system for cholesterol esterase production, we carried out RNA sequencing analyses to screen strongly active promoters in FERMP-21014. Based on gene expression consistency analysis, we selected nine genes that were consistently expressed at high levels, following which we constructed expression vectors using their promoter sequences and achieved overproduction of extracellular cholesterol esterase under fatty acid-free conditions. Of the tested promoters, the promoter of BSFP_0720, which encodes the alkyl hydroperoxide reductase subunit AhpC, resulted in the highest cholesterol esterase activity (24.3 U mL−1). This activity level was 243-fold higher than that of the wild-type strain under fatty acid-free conditions. We confirmed that cholesterol esterase was secreted without excessive accumulation within the cells. The gene expression consistency analysis will be useful to screen promoters applicable to the overexpression of other industrially important enzymes.

Improvement of the Activity of a Fungal Versatile-Lipase Toward Triglycerides: An in silico Mechanistic Description

Some enzymes that belong to the Candida rugosa-like lipase family (abH03. 01) combine the activities of lipases and sterol esterases. Thus, they can act on water-insoluble carboxylic esters releasing long-chain fatty acids but also on sterol esters, although with different activity and affinity. The differences in the catalytic properties among the proteins of this family are explained by small changes in the hydrophobicity of some regions. One of such versatile enzymes is the sterol esterase/lipase from Ophiostoma piceae (OPE) that acts very efficiently on the two types of substrates. Structurally, OPE is characterized by the presence of a lid formed by a α-helix and two 3₁₀-helices rich in hydrophobic amino acids. In this study, the ope gene was modified by directed mutagenesis in order to change specific amino acids in the lid region to modify its structure with the aim of increasing its hydrophobicity. Several recombinant forms of OPE were heterologously produced in Pichia pastoris. In silico molecular dynamics simulations have been used to decipher the mechanistic principles behind the improvements in substrate catalysis. The analyses suggested that the enhanced activity toward hydrophobic substrates such as triglycerides could be due to a better stabilization of the substrate in the lid region as a result of an increased hydrophobicity and an improved topology. These results indicate that in silico simulations can be useful for the optimization of the activity of lipases from the C. rugose-like family for different biotechnological applications.

Atypical organic-solvent tolerant bacterial hormone sensitive lipase-like homologue EstAG1 from Staphylococcus saprophyticus AG1: Synthesis and characterization

Biocatalysts exerting activity against ester bonds have a broad range of applications in modern biotechnology. Some of the most industrially relevant enzymes of this type are lipolytic and their market is predicted to uphold leadership up till 2024. In this study, a novel bacterial hormone-sensitive lipase-like (bHSL) family homologue, designated EstAG1, was discovered by mining gDNA of bacteria isolated from fat contaminated soil in Lithuania. Putative lipolytic enzyme was cloned, overexpressed in E. coli, purified and characterized determining its biochemical properties. While the true physiological role of the discovered leaderless, ~36 kDa enzyme is unknown, metal-activated EstAG1 possessed optima at 45-47.5 °C, pH 7.5-8, with a generally intermediate activity profile between esterases and lipases. Furthermore, EstAG1 was hyperactivated by ethanol, dioxane and DMSO, implicating that it could be industrially applicable enzyme for the synthesis of valuable products such as biodiesel, flavor esters, etc. Sequence analysis and structure modeling revealed that the highest sequence homology of EstAG1 with the closest structurally and functionally described protein makes up only 26%. It was also revealed that EstAG1 has some differences in the bHSL family-characteristic conserved sequence motives. Therefore, EstAG1 presents interest both in terms of biotechnological applications and basic research.

Identification of lipolytic enzymes isolated from bacteria indigenous to Eucalyptus wood species for application in the pulping industry

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Phenol red screening plates is the best method for detecting lipolytic activity.

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Substrate specificity is affected by temperature and pH.

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Essential to test substrates at various pH and temperature to determine optima.

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Lipolytic enzymes indigenous to Eucalyptus sp. can assist in pitch control.

This study highlights the importance of determining substrate specificity at variable experimental conditions. Lipases and esterases were isolated from microorganisms cultivated from Eucalyptus wood species and then concentrated (cellulases removed) and characterized. Phenol red agar plates supplemented with 1% olive oil or tributyrin was ascertained to be the most favourable method of screening for lipolytic activity. Lipolytic activity of the various enzymes were highest at 45–61 U/ml at the optimum temperature and pH of between at 30–35 °C and pH 4–5, respectively. Change in pH influenced the substrate specificity of the enzymes tested. The majority of enzymes tested displayed a propensity for longer aliphatic acyl chains such as dodecanoate (C₁₂), myristate (C₁₄), palmitate (C₁₆) and stearate (C₁₈) indicating that they could be characterised as potential lipases. Prospective esterases were also detected with specificity towards acetate (C₂), butyrate (C₄) and valerate (C₅). Enzymes maintained up to 95% activity at the optimal pH and temperature for 2–3 h. It is essential to test substrates at various pH and temperature when determining optimum activity of lipolytic enzymes, a method rarely employed. The stability of the enzymes at acidic pH and moderate temperatures makes them excellent candidates for application in the treatment of pitch during acid bi-sulphite pulping, which would greatly benefit the pulp and paper industry.

Complete Genome Sequence of Burkholderia stabilis FERMP-21014

Cholesterol esterase (EC 3.1.1.13) was identified in a bacterium, Burkholderia stabilis strain FERMP-21014. Here, we report the complete genome sequence of B. stabilis FERMP-21014, which has been used in the commercial production of cholesterol esterase. The genome sequence information may be useful for improving production levels of cholesterol esterase.

Structure of deformed wing virus, a major honey bee pathogen

The worldwide population of western honey bees (Apis mellifera) is under pressure from habitat loss, environmental stress, and pathogens, particularly viruses that cause lethal epidemics. Deformed wing virus (DWV) from the family Iflaviridae, together with its vector, the mite Varroa destructor, is likely the major threat to the world's honey bees. However, lack of knowledge of the atomic structures of iflaviruses has hindered the development of effective treatments against them. Here, we present the virion structures of DWV determined to a resolution of 3.1 Å using cryo-electron microscopy and 3.8 Å by X-ray crystallography. The C-terminal extension of capsid protein VP3 folds into a globular protruding (P) domain, exposed on the virion surface. The P domain contains an Asp-His-Ser catalytic triad that is, together with five residues that are spatially close, conserved among iflaviruses. These residues may participate in receptor binding or provide the protease, lipase, or esterase activity required for entry of the virus into a host cell. Furthermore, nucleotides of the DWV RNA genome interact with VP3 subunits. The capsid protein residues involved in the RNA binding are conserved among honey bee iflaviruses, suggesting a putative role of the genome in stabilizing the virion or facilitating capsid assembly. Identifying the RNA-binding and putative catalytic sites within the DWV virion structure enables future analyses of how DWV and other iflaviruses infect insect cells and also opens up possibilities for the development of antiviral treatments.

Evolutionary history of versatile-lipases from Agaricales through reconstruction of ancestral structures

BACKGROUND

Fungal "Versatile carboxylic ester hydrolases" are enzymes with great biotechnological interest. Here we carried out a bioinformatic screening to find these proteins in genomes from Agaricales, by means of searching for conserved motifs, sequence and phylogenetic analysis, and three-dimensional modeling. Moreover, we reconstructed the molecular evolution of these enzymes along the time by inferring and analyzing the sequence of ancestral intermediate forms.

RESULTS

The properties of the ancestral candidates are discussed on the basis of their three-dimensional structural models, the hydrophobicity of the lid, and the substrate binding intramolecular tunnel, revealing all of them featured properties of these enzymes. The evolutionary history of the putative lipases revealed an increase on the length and hydrophobicity of the lid region, as well as in the size of the substrate binding pocket, during evolution time. These facts suggest the enzymes' specialization towards certain substrates and their subsequent loss of promiscuity.

CONCLUSIONS

These results bring to light the presence of different pools of lipases in fungi with different habitats and life styles. Despite the consistency of the data gathered from reconstruction of ancestral sequences, the heterologous expression of some of these candidates would be essential to corroborate enzymes' activities.

Virion Structure of Iflavirus Slow Bee Paralysis Virus at 2.6-Angstrom Resolution

The western honeybee (Apis mellifera) is the most important commercial insect pollinator. However, bees are under pressure from habitat loss, environmental stress, and pathogens, including viruses that can cause lethal epidemics. Slow bee paralysis virus (SBPV) belongs to the Iflaviridae family of nonenveloped single-stranded RNA viruses. Here we present the structure of the SBPV virion determined from two crystal forms to resolutions of 3.4 Å and 2.6 Å. The overall structure of the virion resembles that of picornaviruses, with the three major capsid proteins VP1 to 3 organized into a pseudo-T3 icosahedral capsid. However, the SBPV capsid protein VP3 contains a C-terminal globular domain that has not been observed in other viruses from the order Picornavirales. The protruding (P) domains form “crowns” on the virion surface around each 5-fold axis in one of the crystal forms. However, the P domains are shifted 36 Å toward the 3-fold axis in the other crystal form. Furthermore, the P domain contains the Ser-His-Asp triad within a surface patch of eight conserved residues that constitutes a putative catalytic or receptor-binding site. The movements of the domain might be required for efficient substrate cleavage or receptor binding during virus cell entry. In addition, capsid protein VP2 contains an RGD sequence that is exposed on the virion surface, indicating that integrins might be cellular receptors of SBPV.

IMPORTANCE Pollination by honeybees is needed to sustain agricultural productivity as well as the biodiversity of wild flora. However, honeybee populations in Europe and North America have been declining since the 1950s. Honeybee viruses from the Iflaviridae family are among the major causes of honeybee colony mortality. We determined the virion structure of an Iflavirus, slow bee paralysis virus (SBPV). SBPV exhibits unique structural features not observed in other picorna-like viruses. The SBPV capsid protein VP3 has a large C-terminal domain, five of which form highly prominent protruding “crowns” on the virion surface. However, the domains can change their positions depending on the conditions of the environment. The domain includes a putative catalytic or receptor binding site that might be important for SBPV cell entry.