Inactivation of pig heart alanine aminotransferase by beta-chloroalanine

An Alanine Aminotransferase Is Required for Biofilm-Specific Resistance of Aspergillus fumigatus to Echinocandin Treatment

Alanine metabolism has been suggested as an adaptation strategy to oxygen limitation in organisms ranging from plants to mammals. Within the pulmonary infection microenvironment, Aspergillus fumigatus forms biofilms with steep oxygen gradients defined by regions of oxygen limitation. An alanine aminotransferase, AlaA, was observed to function in alanine catabolism and is required for several aspects of A. fumigatus biofilm physiology. Loss of alaA, or its catalytic activity, results in decreased adherence of biofilms through a defect in the maturation of the extracellular matrix polysaccharide galactosaminogalactan (GAG). Additionally, exposure of cell wall polysaccharides is also impacted by loss of alaA, and loss of AlaA catalytic activity confers increased biofilm susceptibility to echinocandin treatment, which is correlated with enhanced fungicidal activity. The increase in echinocandin susceptibility is specific to biofilms, and chemical inhibition of alaA by the alanine aminotransferase inhibitor β-chloro-l-alanine is sufficient to sensitize A. fumigatus biofilms to echinocandin treatment. Finally, loss of alaA increases susceptibility of A. fumigatus to in vivo echinocandin treatment in a murine model of invasive pulmonary aspergillosis. Our results provide insight into the interplay of metabolism, biofilm formation, and antifungal drug resistance in A. fumigatus and describe a mechanism of increasing susceptibility of A. fumigatus biofilms to the echinocandin class of antifungal drugs. IMPORTANCE Aspergillus fumigatus is a ubiquitous filamentous fungus that causes an array of diseases depending on the immune status of an individual, collectively termed aspergillosis. Antifungal therapy for invasive pulmonary aspergillosis (IPA) or chronic pulmonary aspergillosis (CPA) is limited and too often ineffective. This is in part due to A. fumigatus biofilm formation within the infection environment and the resulting emergent properties, particularly increased antifungal resistance. Thus, insights into biofilm formation and mechanisms driving increased antifungal drug resistance are critical for improving existing therapeutic strategies and development of novel antifungals. In this work, we describe an unexpected observation where alanine metabolism, via the alanine aminotransferase AlaA, is required for several aspects of A. fumigatus biofilm physiology, including resistance of A. fumigatus biofilms to the echinocandin class of antifungal drugs. Importantly, we observed that chemical inhibition of alanine aminotransferases is sufficient to increase echinocandin susceptibility and that loss of alaA increases susceptibility to echinocandin treatment in a murine model of IPA. AlaA is the first gene discovered in A. fumigatus that confers resistance to an antifungal drug specifically in a biofilm context.

Exposure to L-cycloserine incurs survival costs and behavioral alterations in Aedes aegypti females

Background

It was previously demonstrated that alanine aminotransferase (ALAT, EC 2.6.1.2) participates in maintaining the alanine-proline cycle between flight muscles and fat body during Aedes aegypti flight. ALAT is also actively involved in the metabolism of ammonia in A. aegypti. Here, we investigated the survival and behavioral costs of ALAT inhibition in A. aegypti females to better understand the role of ALAT in blood-fed mosquitoes.

Methods

We analyzed how A. aegypti female mosquitoes respond to blood meals supplemented with 0, 2.5, 5 and 10 mM L-cycloserine, a well-known inhibitor of ALAT in animals. Mosquitoes were also exposed to blood meals supplemented with L-cycloserine and different concentrations of glucose (0, 10 and 100 mM). Additionally, the effects of ALAT inhibitor and glucose in mosquitoes starved for 24 or 48 h were investigated. Survival and behavioral phenotypes were analyzed during a time course (1, 2, 4, 6, 12, 24, 48 and 72 h after feeding).

Results

L-cycloserine at 10 mM resulted in high mortality relative to control, with an acute effect during the first 6 h after treatment. A significant decrease in the number of active mosquitoes coinciding with an increase in futile wing fanning during the first 24 h was observed at all inhibitor concentrations. A high occurrence of knockdown phenotype was also recorded at this time for both 5 and 10 mM L-cycloserine. The supplementation of glucose in the blood meal amplified the effects of the ALAT inhibitor. In particular, we observed a higher mortality rate concomitant with an increase in the knockdown phenotype. Starvation prior to blood feeding also increased the effects of L-cycloserine with a rapid increase in mortality.

Conclusions

Our results provide evidence that exposure of high doses of L-cycloserine during A. aegypti blood feeding affects mosquito survival and motor activity, suggesting an interference with carbohydrate and ammonia metabolism in a time-dependent manner.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-3305-7-373) contains supplementary material, which is available to authorized users.

Inhibition of alanine aminotransferase in silico and in vivo promotes mitochondrial metabolism to impair malignant growth

Cancer cells commonly exhibit increased nonoxidative d-glucose metabolism whereas induction of mitochondrial metabolism may impair malignant growth. We have first used an in silico method called elementary mode analysis to identify inhibition of ALAT (l-alanine aminotransferase) as a putative target to promote mitochondrial metabolism. We then experimentally show that two competitive inhibitors of ALAT, l-cycloserine and β-chloro-l-alanine, inhibit l-alanine production and impair d-glucose uptake of LLC1 Lewis lung carcinoma cells. The latter inhibition is linked to an initial energy deficit, as quantified by decreased ATP content, which is then followed by an activation of AMP-activated protein kinase and subsequently increased respiration rates and mitochondrial production of reactive oxygen species, culminating in ATP replenishment in ALAT-inhibited LLC1 cells. Moreover, we observe altered phosphorylation of p38 MAPK (mitogen-activated protein kinase 14), ERK (extracellular signal-regulated kinase 1/2), and Rb1 (retinoblastoma 1) proteins, as well as decreased expression of Cdc25a (cell decision cycle 25 homolog A) and Cdk4 (cyclin-dependent kinase 4). Importantly, these sequelae of ALAT inhibition culminate in similarly reduced anchorage-dependent and anchorage-independent growth rates of LLC1 cells, together suggesting that inhibition of ALAT efficiently impairs cancer growth by counteracting the Warburg effect due to compensatory activation of mitochondrial metabolism.

Mechanisms of cysteine S-conjugate beta-lyases

Mercapturic acids are conjugates of S-(N-acetyl)-L-cysteine formed during the detoxification of xenobiotics and during the metabolism of such endogenous agents as estrogens and leukotrienes. Many mercaturates are formed from the corresponding glutathione S-conjugates. This chapter focuses on (a) the discovery of the cysteine S-conjugate beta-lyases; (b) the involvement of pyridoxal-5-phosphate; (c) the influence of the electron-withdrawing properties of the group attached to the sulfur atom; and (d) the potential of cysteine S-conjugates as pro-drugs.

Chemistry of the inactivation of cytosolic aspartate aminotransferase by serine O-sulfate

The reaction of serine O-sulfate with cytosolic aspartate aminotransferase [John, R.A., & Fasella, P. (1969) Biochemistry 8, 4477] has been reinvestigated. As in the corresponding reaction with beta-chloroalanine [Morino, Y., Osman, A.M., & Okamoto, M. (1974) J. Biol. Chem. 249, 6684], the enzyme is inactivated over a 10-min period, and the absorption maximum at pH 5.4 shifts from 430 to 336 nm. Upon prolonged standing the peak shifts again over a period of 20 h to 455 nm, a behavior entirely similar to that reported by Morino et al. for beta-chloroalanine in the presence of 3 M formate. When the pH of either the 10-min product (1a) or the 20-h product (1b) is raised to 11 or above, a yellow, diffusible compound (2) is released from the protein. This compound as well as its dephosphorylation and reduction products has been isolated and studied by NMR spectroscopy. Compound 2 is identical with a compound formed from serine sulfate and glutamate decarboxylase by a similar reaction sequence [Likos, J.J., Ueno, H., Feldhaus, R.W., & Metzler, D.E. (1982) Biochemistry (preceding paper in this issue)] and is the product of an aldol condensation of pyruvate with pyridoxal phosphate. When the 20-h product 1b is reduced with sodium borohydride and then heated in a boiling water bath, a material identical with the reduction product of 2 is released. We propose that the 20-h product 1b consists of 2 bound to the enzyme. Pathways for the formation of the various compounds are proposed. These findings require a reevaluation of the mechanisms of action of many enzyme-activated inhibitors of pyridoxal phosphate dependent enzymes.

Pyridoxal 5'-phosphate binding site of pig heart alanine aminotransferase

After borohydride reduction, carboxymethylation, and tryptic digestion of the holoenzyme of pig heart alanine aminotransferase, a single icosapeptide containing the N6-(phosphopyridoxyl)lysine residue was isolated by a combination of gel filtration and ion-exchange chromatogrpahy. Its primary structure was determined as Gln-Glu-Leu-Ala-Ser-Phe-His-Ser-Val-Ser-Lsy(Pxy)-Gly-Phe-Met-Gly-Glu-Cys-Gly-Phe-Arg.