Rhizobium etli asparaginase II: an alternative for acute lymphoblastic leukemia (ALL) treatment

A Structural In Silico Analysis of the Immunogenicity of L-Asparaginase from Penicillium cerradense

L-asparaginase is an essential drug used to treat acute lymphoid leukemia (ALL), a cancer of high prevalence in children. Several adverse reactions associated with L-asparaginase have been observed, mainly caused by immunogenicity and allergenicity. Some strategies have been adopted, such as searching for new microorganisms that produce the enzyme and applying protein engineering. Therefore, this work aimed to elucidate the molecular structure and predict the immunogenic profile of L-asparaginase from Penicillium cerradense, recently revealed as a new fungus of the genus Penicillium and producer of the enzyme, as a motivation to search for alternatives to bacterial L-asparaginase. In the evolutionary relationship, L-asparaginase from P. cerradense closely matches Aspergillus species. Using in silico tools, we characterized the enzyme as a protein fragment of 378 amino acids (39 kDa), including a signal peptide containing 17 amino acids, and the isoelectric point at 5.13. The oligomeric state was predicted to be a homotetramer. Also, this L-asparaginase presented a similar immunogenicity response (T- and B-cell epitopes) compared to Escherichia coli and Dickeya chrysanthemi enzymes. These results suggest a potentially useful L-asparaginase, with insights that can drive strategies to improve enzyme production.

Molecular Analysis of L-Asparaginases for Clarification of the Mechanism of Action and Optimization of Pharmacological Functions

L-asparaginases (EC 3.5.1.1) are a family of enzymes that catalyze the hydrolysis of L-asparagine to L-aspartic acid and ammonia. These proteins with different biochemical, physicochemical and pharmacological properties are found in many organisms, including bacteria, fungi, algae, plants and mammals. To date, asparaginases from E. coli and Dickeya dadantii (formerly known as Erwinia chrysanthemi) are widely used in hematology for the treatment of lymphoblastic leukemias. However, their medical use is limited by side effects associated with the ability of these enzymes to hydrolyze L-glutamine, as well as the development of immune reactions. To solve these issues, gene-editing methods to introduce amino-acid substitutions of the enzyme are implemented. In this review, we focused on molecular analysis of the mechanism of enzyme action and to optimize the antitumor activity.

Encapsulation of Asparaginase as a Promising Strategy to Improve In Vivo Drug Performance

Asparaginase (ASNase) is a widely applied chemotherapeutic drug that is used to treat Acute Lymphoblastic Leukemia (ALL); however, immune responses and silent inactivation of the drug often limit its bioavailability. Many strategies have been proposed to overcome these drawbacks, including the development of improved formulations (biobetters), but only two of them are currently on the market. Nano- and micro-encapsulation are some of the most promising and novel approaches to enhance in vivo performance of ASNase, preventing the direct contact of the enzyme with the environment, protecting it from protease degradation, increasing the enzymes catalytic half-life, and in some cases, reducing immunogenicity. This review summarizes the strategies, particularly for ASNase nano- and micro-encapsulation, and their main findings, constraints, and current gaps in the state-of-the-art knowledge. The pros and cons of the use of different nanocarriers are discussed with the idea to ultimately provide safer and more effective treatments for patients with ALL.

Crystal structures of the elusive Rhizobium etli L-asparaginase reveal a peculiar active site

Rhizobium etli, a nitrogen-fixing bacterial symbiont of legume plants, encodes an essential L-asparaginase (ReAV) with no sequence homology to known enzymes with this activity. High-resolution crystal structures of ReAV show indeed a structurally distinct, dimeric enzyme, with some resemblance to glutaminases and β-lactamases. However, ReAV has no glutaminase or lactamase activity, and at pH 9 its allosteric asparaginase activity is relatively high, with Km for L-Asn at 4.2 mM and kcat of 438 s-1. The active site of ReAV, deduced from structural comparisons and confirmed by mutagenesis experiments, contains a highly specific Zn2+ binding site without a catalytic role. The extensive active site includes residues with unusual chemical properties. There are two Ser-Lys tandems, all connected through a network of H-bonds to the Zn center, and three tightly bound water molecules near Ser48, which clearly indicate the catalytic nucleophile.

Structural and biophysical aspects of l-asparaginases: a growing family with amazing diversity

l-Asparaginases have remained an intriguing research topic since their discovery ∼120 years ago, especially after their introduction in the 1960s as very efficient antileukemic drugs. In addition to bacterial asparaginases, which are still used to treat childhood leukemia, enzymes of plant and mammalian origin are now also known. They have all been structurally characterized by crystallography, in some cases at outstanding resolution. The structural data have also shed light on the mechanistic details of these deceptively simple enzymes. Yet, despite all this progress, no better therapeutic agents have been found to beat bacterial asparaginases. However, a new option might arise with the discovery of yet another type of asparaginase, those from symbiotic nitrogen-fixing Rhizobia, and with progress in the protein engineering of enzymes with desired properties. This review surveys the field of structural biology of l-asparaginases, focusing on the mechanistic aspects of the well established types and speculating about the potential of the new members of this amazingly diversified family.

Asparaginase-Phage P22 Nanoreactors: Toward a Biobetter Development for Acute Lymphoblastic Leukemia Treatment

Asparaginase (ASNase) is a biopharmaceutical for Acute Lymphoblastic Leukemia (ALL) treatment. However, it shows undesirable side effects such as short lifetimes, susceptibility to proteases, and immunogenicity. Here, ASNase encapsidation was genetically directed in bacteriophage P22-based virus-like particles (VLPs) (ASNase-P22 nanoreactors) as a strategy to overcome these challenges. ASNase-P22 was composed of 58.4 ± 7.9% of coat protein and 41.6 ± 8.1% of tetrameric ASNase. Km and Kcat values of ASNase-P22 were 15- and 2-fold higher than those obtained for the free enzyme, respectively. Resulting Kcat/Km value was 2.19 × 10⁵ M⁻¹ s⁻¹. ASNase-P22 showed an aggregation of 60% of the volume sample when incubated at 37 °C for 12 days. In comparison, commercial asparaginase was completely aggregated under the same conditions. ASNase-P22 was stable for up to 24 h at 37 °C, independent of the presence of human blood serum (HBS) or whether ASNase-P22 nanoreactors were uncoated or PEGylated. Finally, we found that ASNase-P22 caused cytotoxicity in the leukemic cell line MOLT-4 in a concentration dependent manner. To our knowledge, this is the first work where ASNase is encapsulated inside of VLPs, as a promising alternative to fight ALL.

Identification of L-asparaginases from Streptomyces strains with competitive activity and immunogenic profiles: a bioinformatic approach

The enzyme L-asparaginase from Escherichia coli is a therapeutic enzyme that has been a cornerstone in the clinical treatment of acute lymphoblastic leukemia for the last decades. However, treatment effectiveness is limited by the highly immunogenic nature of the protein and its cross-reactivity towards L-glutamine. In this work, a bioinformatic approach was used to identify, select and computationally characterize L-asparaginases from Streptomyces through sequence-based screening analyses, immunoinformatics, homology modeling, and molecular docking studies. Based on its predicted low immunogenicity and excellent enzymatic activity, we selected a previously uncharacterized L-asparaginase from Streptomyces scabrisporus. Furthermore, two putative asparaginase binding sites were identified and a 3D model is proposed. These promising features allow us to propose L-asparaginase from S. scabrisporus as an alternative for the treatment of acute lymphocytic leukemia.

Structure and function insights garnered from in silico modeling of the thrombospondin type-1 domain-containing 7A antigen

The thrombospondin type-1 domain containing 7A (THSD7A) protein is known to be one of the antigens responsible for the autoimmune disorder idiopathic membranous nephropathy. The structure of this antigen is currently unsolved experimentally. Here we present a homology model of the extracellular portion of the THSD7A antigen. The structure was evaluated for folding patterns, epitope site prediction, and function was predicted. Results show that this protein contains 21 extracellular domains and with the exception of the first two domains, has a regular repeating pattern of TSP-1-like followed by F-spondin-like domains. Our results indicate the presence of a novel Trp-ladder sequence of WxxxxW in the TSP-1-like domains. Of the 21 domains, 18 were shown to have epitope binding sites as predicted by epitopia. Several of the F-spondin-like domains have insertions in the canonical TSP fold, most notably the coiled coil region in domain 4, which may be utilized in protein-protein binding interactions, suggesting that this protein functions as a heparan sulfate binding site.

Genetic and metabolic engineering approaches for the production and delivery of L-asparaginases: An overview

L-asparaginase is one of the protein drugs for countering leukemia and lymphoma. A major challenge in the therapeutic potential of the enzyme is its immunogenicity, low-plasma half-life and glutaminase activity that are found to be the reasons for toxicities attributed to asparaginase therapy. For addressing these challenges, several research and developmental activities are going on throughout the world for an effective drug delivery for treatment of cancer. Hence there is an urgent need for the development of asparaginase with improved properties for efficient drug delivery. The strategies selected should be economically viable to ensure the availability of the drug at low cost. The current review addresses various strategies adopted for the production of asparaginase from different sources, approaches for increasing the therapeutic efficiency of the protein and new drug delivery systems for L-asparaginase.