RESUMO
EF-hand is a common motif in Ca2+-binding proteins, some of which present a conformational change upon Ca2+-binding, a relevant property for signal transduction. In the present work, we investigated the behavior of Calbindin D9k, a modulator protein with a high affinity for Ca2+ but structurally insensitive to its presence. Its non-canoncal N-terminal EF-hand was replaced by chimeric motifs, containing increasing structural elements from the sensor troponin C SCIII motif. We demonstrated that the loop and helix II were the necessary elements for a conformational change promoted by calcium in chimeric Calbindin D9k. Fusion of the isolated chimeric motifs to an activity reporter gene showed the loop as the minimal element to promote a conformational change. The discrepancy between these results is discussed in the light of inter-motif interactions and helix I participation in modulating the Ca2+ affinity and restricting motif conformation.
Assuntos
Cálcio/metabolismo , Proteína G de Ligação ao Cálcio S100/metabolismo , Sequência de Aminoácidos , Dicroísmo Circular , Motivos EF Hand , Modelos Moleculares , Ligação Proteica , Conformação Proteica , Proteína G de Ligação ao Cálcio S100/químicaRESUMO
The Cyt and Cry toxins are different pore-forming proteins produced by Bacillus thuringiensis bacteria, and used in insect-pests control. Cry-toxins have a complex mechanism involving interaction with several proteins in the insect gut such as aminopeptidase N (APN), alkaline phosphatase (ALP) and cadherin (CAD). It was shown that the loop regions of domain II of Cry toxins participate in receptor binding. Cyt-toxins are dipteran specific and interact with membrane lipids. We show that Cry1Ab domain II loop3 is involved in binding to APN, ALP and CAD receptors since point mutation Cry1Ab-G439D affected binding to these proteins. We hypothesized that construction of Cyt1A-hybrid proteins providing a binding site that recognizes gut proteins in lepidopteran larvae could result in improved Cyt1Aa toxin toward lepidopteran larvae. We constructed hybrid Cyt1Aa-loop3 proteins with increased binding interaction to Manduca sexta receptors and increased toxicity against two Lepidopteran pests, M. sexta and Plutella xylostella. The hybrid Cyt1Aa-loop3 proteins were severely affected in mosquitocidal activity and showed partial hemolytic activity but retained their capacity to synergize Cry11Aa toxicity against mosquitos. Our data show that insect specificity of Cyt1Aa toxin can be modified by introduction of loop regions from another non-related toxin with different insect specificity.
Assuntos
Aedes/efeitos dos fármacos , Bacillus thuringiensis/metabolismo , Proteínas de Bactérias/genética , Endotoxinas/genética , Proteínas Hemolisinas/genética , Proteínas de Insetos/metabolismo , Inseticidas , Mariposas/metabolismo , Animais , Bacillus thuringiensis/genética , Toxinas de Bacillus thuringiensis , Proteínas de Bactérias/isolamento & purificação , Proteínas de Bactérias/toxicidade , Bioensaio/métodos , Endotoxinas/isolamento & purificação , Endotoxinas/toxicidade , Proteínas Hemolisinas/isolamento & purificação , Proteínas Hemolisinas/toxicidade , Proteínas de Insetos/isolamento & purificação , Larva/efeitos dos fármacos , Mutagênese Sítio-Dirigida , Ligação Proteica/genética , Proteínas Recombinantes/genética , Proteínas Recombinantes/isolamento & purificação , Proteínas Recombinantes/toxicidade , Especificidade por Substrato/genética , Testes de Toxicidade/métodosRESUMO
Recombinant protein expression is one of the key issues in protein engineering and biotechnology. Among the different models for assessing protein production and structure-function studies, green fluorescent protein (GFP) is one of the preferred models because of its importance as a reporter in cellular and molecular studies. In this research we analyze the effect of codon deletions near the amino terminus of different GFP proteins on fluorescence. Our study includes Gly4 deletions in the enhanced GFP (EGFP), the red-shifted GFP and the red-shifted EGFP. The Gly4 deletion mutants and their corresponding wild-type counterparts were transcribed under the control of the T7 or Trc promoters and their expression patterns were analyzed. Different fluorescent outcomes were observed depending on the type of fluorescent gene versions. In silico analysis of the RNA secondary structures near the ribosome binding site revealed a direct relationship between their minimum free energy and GFP production. Integrative analysis of these results, including SDS-PAGE analysis, led us to conclude that the fluorescence improvement of cells expressing different versions of GFPs with Gly4 deleted is due to an enhancement of the accessibility of the ribosome binding site by reducing the stability of the RNA secondary structures at their mRNA leader regions.
Assuntos
Códon , Expressão Gênica , Proteínas de Fluorescência Verde/biossíntese , Proteínas de Fluorescência Verde/genética , Deleção de Sequência , Biologia Computacional , Fluorometria , Conformação de Ácido Nucleico , RNA Mensageiro/química , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Proteínas Recombinantes/biossíntese , Proteínas Recombinantes/genética , Ribossomos/metabolismoRESUMO
The T-protein is a single-polypeptide bi-functional enzyme composed of a chorismate mutase domain fused to a prephenate dehydrogenase domain (TyrA). We replaced the chorismate mutase domain with canonical or pseudo-Ca(2+)-binding motifs (EF-hand). Canonical-EF-hand-motifs differentiate from pseudo-EF-hand-motifs by experimenting a Ca(2+)-dependent conformational change. The Ca(2+)-free EF-hand-TyrA fusion-proteins showed TyrA activity at the T-protein level. Canonical-EF-hand-TyrA fusions showed a Ca(2+)-dependent loss of TyrA activity, but a pseudo-EF-hand-TyrA fusion showed high TyrA activity level in excess-Ca(2+) conditions. Because TyrA activity exhibits robust changes in response to Ca(2+)-dependent-EF-hand conformational alterations, TyrA could be a good Ca(2+)-reporter enzyme. A chimeric canonical/pseudo-EF-hand strategy is proposed to confer pseudo-EF-hand motifs with a Ca(2+)-dependent conformational change.
Assuntos
Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Complexos Multienzimáticos/química , Complexos Multienzimáticos/metabolismo , Motivos de Aminoácidos , Sequência de Aminoácidos , Substituição de Aminoácidos , Proteínas de Bactérias/genética , Cálcio/metabolismo , Sequência Conservada , Escherichia coli/genética , Escherichia coli/metabolismo , Dados de Sequência Molecular , Complexos Multienzimáticos/genética , Prefenato Desidrogenase/química , Prefenato Desidrogenase/genética , Prefenato Desidrogenase/metabolismo , Conformação Proteica , Estrutura Terciária de Proteína , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismoRESUMO
T-protein is composed of chorismate mutase (AroQ(T)) fused to the N-terminus of prephenate dehydrogenase (TyrA). Here, we report the replacement of AroQ(T) with the ß1-domain of protein G (Gß1). The TyrA domain shows a strong dehydrogenase activity within the context of this fusion, and our data indicate that Gß1-TyrA folds into a dimeric conformation. Amino acid substitutions in the Gß1 domain of Gß1-TyrA identified residues involved in stabilizing the TyrA dimeric conformation. Gß1 substitutions in the N-terminal ß-hairpin eliminated Gß1-TyrA expression, whereas Gß1-TyrA tolerated Gß1 substitutions in the C-terminal ß-hairpin and in the α-helix. All of the characterized variants folded into a dimeric conformation. The importance of the ß2-strand in forming a Gß1 homo-dimerization interface explains the relevance of the first-ß-hairpin in stabilizing the dimeric TyrA protein.
Assuntos
Proteínas de Bactérias/química , Corismato Mutase/química , Proteínas de Escherichia coli/química , Complexos Multienzimáticos/química , Prefenato Desidrogenase/química , Sequência de Aminoácidos , Substituição de Aminoácidos , Proteínas de Bactérias/genética , Corismato Mutase/genética , Dimerização , Proteínas de Escherichia coli/genética , Modelos Moleculares , Dados de Sequência Molecular , Complexos Multienzimáticos/genética , Prefenato Desidrogenase/genética , Dobramento de Proteína , Estrutura Terciária de Proteína , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genética , Homologia de Sequência de AminoácidosRESUMO
L-phenylalanine (L-Phe) is an aromatic amino acid with diverse commercial applications. Technologies for industrial microbial synthesis of L-Phe using glucose as a starting raw material currently achieve a relatively low conversion yield (Y(Phe/Glc)). The purpose of this work was to study the effect of PTS (phosphotransferase transport system) inactivation and overexpression of different versions of feedback inhibition resistant chorismate mutase-prephenate dehydratase (CM-PDT) on the yield (Y(Phe/Glc)) and productivity of L-Phe synthesized from glucose. The E. coli JM101 strain and its mutant derivative PB12 (PTS(-)Glc(+) phenotype) were used as hosts. PB12 has an inactive PTS, but is capable of transporting and phosphorylating glucose by using an alternative system constituted by galactose permease (GalP) and glucokinase activities (Glk). JM101 and PB12 were transformed with three plasmids, harboring genes that encode for a feedback inhibition resistant DAHP synthase (aroG(fbr)), transketolase (tktA) and either a truncated CM-PDT (pheA(fbr)) or its derived evolved genes (pheA(ev1) or pheA(ev2)). Resting-cells experiments with these engineered strains showed that JM101 and PB12 strains expressing either pheA(ev1) or pheA(ev2) genes produced l-Phe from glucose with Y(Phe/Glc) of 0.21 and 0.33 g/g, corresponding to 38 and 60% of the maximum theoretical yield (0.55 g/g), respectively. In addition, in both engineered strains the reached q(Phe) high levels of 40 mg/g-dcw.h. The metabolic engineering strategy followed in this work, including a strain with an inactive PTS, resulted in a positive impact over the Y(Phe/Glc), enhancing it nearly 57% compared with its PTS(+) counterpart. This is the first report wherein PTS inactivation was a successful strategy to improve the Y(Phe/Glc).