Information accumulated over the past decades on the physiological functions and metabolic pathways of biosynthesis and degradation of D-amino acids has led to a renewed interest in their study. These isomers are known to form both in nature and during the chemical synthesis of L-amino acids for feeding and pharmacological purposes, as well as in the industrial processing of some raw materials. This article discusses the positive and negative effects of D-amino acids on the human body, animals and the environment. In addition, the scientific data concerning the mechanisms of cytotoxic action of D-amino acids and their industrial and biomedical potential are summarized. ARTICLE HISTORY

Site-directed mutagenesis of Rhodospirillum rubrum L-asparaginase (RrA) was performed in order to identify sites of the protein molecule important for its therapeutic and physico-chemical properties. Ten multipoint mutant genes were obtained, and five recombinant RrA variants were expressed in E. coli BL21(DE3) cells and isolated as functionally active highly purified proteins. Protein purification was performed using Q-Sepharose and DEAE-Toyopearl chromatography. Overall yield of the active enzymes was 70-80 %, their specific activity at pH 7.4 and 37 °C varied of 140-210 U/mg. L-Glutaminase activity did not exceed 0.01 % of L-asparaginase activity. All RrA mutants showed maximum enzyme activity at pH 9.3-9.5 and 53-58 °C. Km and Vmax values for L-asparagine were evaluated for all mutants. Mutations G86P, D88H, M90K (RrAH), G121L, D123A (RrАI) caused the loss of enzyme activity and confirmed the importance of these sites in the implementation of catalytic functions. Removal of four residues from C-terminal area of the enzyme (RrAK) resulted in the enzyme instability. Mutations D60K, F61L(RrАD), and R118H, G120R(RrАJ) led to the improvement of kinetic parameters and enzyme stabilization. Substitutions E149R, V150P (RrАB) improved antineoplastic and cytotoxic activity of the RrA. A64V, E67K substitutions, especially in combination with E149R, V150P (RrАE), considerably destabilized recombinant enzyme.

Rhodospirillum rubrum L‐asparaginase mutant E149R, V150P, F151T (RrA) down‐regulates telomerase activity due to its ability to inhibit the expression of telomerase catalytic subunit hTERT. The aim of this study was to define the effect of short‐term and long‐term RrA exposure on proliferation of cancer Jurkat cell line and normal human CD4+ T lymphocytes. RrA could inhibit telomerase activity in dose‐ and time‐dependent manner in both Jurkat and normal CD4+ T cells. Continuous RrA exposure of these cells resulted in shortening of telomeres followed by cell cycle inhibition, replicative senescence, and development of apoptosis. Complete death of Jurkat cells was observed at the day 25 of RrA exposure while normal CD4+ T cells died at the day 50 due to the initial longer length of telomeres. Removal of RrA from senescent cells led to a reactivation of hTERT expression, restoration telomerase activity, re‐elongation of telomeres after 48 h of cultivation, and survival of cells. These findings demonstrate that proliferation of cancer and normal telomerase‐positive cells can be limited by continuous telomerase inhibition with RrA. Longer telomeres of normal CD4+ T lymphocytes make such cells more sustainable to RrA exposure that could give them an advantage during anti‐telomerase therapy. These results should facilitate further investigations of RrA as a potent anti‐telomerase therapeutic protein.

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The recombinant producer strain expressing Rhodospirillum rubrum L asparaginase (RrA) has been obtained and a purification procedure of RrA has been developed. The purified enzyme, RrA, has the following biochemical and catalytic characteristics: K m for L Asn of 0.22 mM, pH optimum at 9.2; temper ature optimum at 54°C, pI = 5.1. RrA exhibited a significant cytotoxic effect towards the following cell lines: K562 (IC 50 = 1.80 U/mL), DU145 (IC 50 = 9.19 U/mL), and MDA MB 231 (IC 50 = 34.62 U/mL). Com parative analysis employing E. coli L asparaginase II type (EcA) and Erwinia carotovora L asparaginase (EwA) has shown that the enzyme cytotoxicity towards these cell lines decreased in the following order: EcA > RrA > EwA. Daily administration of RrA (4000 U/kg) to L5178y bearing mice for 10 days (total dose of 40000 U/kg) showed T/C = 172. Data obtained suggest that RrA may be referred to intracellular L aspar aginases with low L glutaminase activity and marked antiproliferative effect.

BackgroundE.coli type II L-asparaginase is widely used for treatment of acute lymphoblastic leukemia. However, serious side effects such as allergic or hypersensitivity reactions are common for L-asparaginase treatment. Methods for minimizing immune response on L-asparaginase treatment in human include bioengeneering of less immunogenic version of the enzyme or utilizing the homologous enzymes of different origin. To rationalize these approaches we compared immunogenicity of L-asparaginases from five bacterial organisms and performed sequence-structure analysis of the presumable epitope regions.MethodsIgG and IgM immune response in C57B16 mice after immunization with Wollinella succinogenes type II (WsA), Yersinia pseudotuberculosis type II (YpA), Erwinia carotovora type II (EwA), and Rhodospirillum rubrum type I (RrA) and Escherichia coli type II (EcA) L-asparaginases was evaluated using standard ELISA method. The comparative bioinformatics analysis of structure and sequence of the bacterial L-asparaginases presumable epitope regions was performed.ResultsWe showed different immunogenic properties of five studied L-asparaginases and confirmed the possibility of replacement of EcA with L-asparaginase from different origin as a second-line treatment. Studied L-asparaginases might be placed in the following order based on the immunogenicity level: YpA > RrA, WsA ≥ EwA > EcA. Most significant cross-immunogenicity was shown between EcA and YpA. We propose that a long N-terminus of YpA enzyme enriched with charged aminoacids and tryptophan could be a reason of higher immunogenicity of YpA in comparison with other considered enzymes. Although the recognized structural and sequence differences in putative epitope regions among five considered L-asparaginases does not fully explain experimental observation of the immunogenicity of the enzymes, the performed analysis set the foundation for further research in this direction.ConclusionsThe performed studies showed different immunogenic properties of L-asparaginases and confirmed the possibility of replacement of EcA with L-asparaginase from different origin. The preferable enzymes for the second line treatment are WsA, RrA, or EwA.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-016-2125-4) contains supplementary material, which is available to authorized users.