Purification and properties of acetate kinase from Acholeplasma laidlawii

Elevated acetate kinase (ackA) gene expression, activity, and biofilm formation observed in methicillin-resistant strains of Staphylococcus aureus (MRSA)

BACKGROUND

Staphylococcus aureus spreads its infections through biofilms. This usually happens in the stationary phase of S. aureus growth where it utilizes accumulated acetate as a carbon source via the phosphotrans-acetylase-acetate kinase (Pta-Ack) pathway. In which acetate kinase (ackA) catalyzes the substrate-level phosphorylation, a vital secondary energy-yielding pathway that promotes biofilms formation aids bacterium survival in hostile environments. In this study, we describe the cloning, sequencing, and expression of S. aureus ackA gene. The expression analysis of ackA gene in methicillin-resistant strains of S. aureus (MRSA) correlates with ackA activity and biofilm units. The uniqueness of ackA was analyzed by using in silico methods.

RESULTS

Elevated ackA gene expression was observed in MRSA strains, which correlates with increased ackA activity and biofilm units, explaining ackA role in MRSA growth and pathogenicity. The pure recombinant acetate kinase showed a molecular weight of 44 kDa, with enzyme activity of 3.35 ± 0.05 μM/ml/min. The presence of ACKA-1, ACKA-2 sites, one ATP, and five serine/threonine-protein kinase sites in the ackA gene (KC954623.1) indicated that acetyl phosphate production is strongly controlled. The comparative structural analysis of S. aureus ackA with ackA structures of Mycobacterium avium (3P4I) and Salmonella typhimurium (3SLC) exhibited variations as indicated by the RMSD values 1.877 Å and 2.141 Å respectively, explaining why ackA functions are differently placed in bacteria, concurring its involvement in S. aureus pathogenesis.

CONCLUSIONS

Overall findings of this study highlight the correlation of ackA expression profoundly increases survival capacity through biofilm formation, which is a pathogenic factor in MRSA and plays a pivotal role in infection spreading.

Acetate as a potential feedstock for the production of value-added chemicals: Metabolism and applications

Acetate is regarded as a promising carbon feedstock in biological production owing to its possible derivation from C₁ gases such as CO, CO₂ and methane. To best use of acetate, comprehensive understanding of acetate metabolisms from genes and enzymes to pathways and regulations is needed. This review aims to provide an overview on the potential of acetate as carbon feedstock for industrial biotechnology. Biochemical, microbial and biotechnological aspects of acetate metabolism are described. Especially, the current state-of-the art in the production of value-added chemicals from acetate is summarized. Challenges and future perspectives are also provided.

Complete Genome Sequence of Mycoplasma arginini Strain HAZ 145_1 from Bovine Mastitic Milk in Japan

Mycoplasma arginini is a species sometimes isolated from bovine specimens, mastitic milk, etc. Its pathogenicity against cows, however, is unspecific, unlike other bovine mycoplasmas. Its whole-genome sequence is needed to comprehend its real image. We present here the 678,592-bp complete genome sequence of M. arginini strain HAZ 145_1.

Complete Genome Sequence of Mycoplasma canadense Strain HAZ 360_1 from Bovine Mastitic Milk in Japan

Bovine mycoplasmal mastitis is spreading quickly among cows. Mycoplasma canadense, a causal species of bovine mastitis, reduces milk quality and quantity via the infiltration of numerous inflammatory cells. Presented here is the complete 693,241-bp genome sequence of M. canadense strain HAZ 360_1, which was isolated in Japan.

Acetate kinase isozymes confer robustness in acetate metabolism

Acetate kinase (ACK) (EC no: 2.7.2.1) interconverts acetyl-phosphate and acetate to either catabolize or synthesize acetyl-CoA dependent on the metabolic requirement. Among all ACK entries available in UniProt, we found that around 45% are multiple ACKs in some organisms including more than 300 species but surprisingly, little work has been done to clarify whether this has any significance. In an attempt to gain further insight we have studied the two ACKs (AckA1, AckA2) encoded by two neighboring genes conserved in Lactococcus lactis (L. lactis) by analyzing protein sequences, characterizing transcription structure, determining enzyme characteristics and effect on growth physiology. The results show that the two ACKs are most likely individually transcribed. AckA1 has a much higher turnover number and AckA2 has a much higher affinity for acetate in vitro. Consistently, growth experiments of mutant strains reveal that AckA1 has a higher capacity for acetate production which allows faster growth in an environment with high acetate concentration. Meanwhile, AckA2 is important for fast acetate-dependent growth at low concentration of acetate. The results demonstrate that the two ACKs have complementary physiological roles in L. lactis to maintain a robust acetate metabolism for fast growth at different extracellular acetate concentrations. The existence of ACK isozymes may reflect a common evolutionary strategy in bacteria in an environment with varying concentrations of acetate.

Suspected utility of enzymes with multiple activities in the small genome Mycoplasma species: the replacement of the missing "household" nucleoside diphosphate kinase gene and activity by glycolytic kinases

The small genome Mollicutes whose DNAs are completely sequenced (Mycoplasma genitalium, Mycoplasma pneumoniae, Mycoplasma pulmonis, and Ureaplasma urealyticum [parvum]) lack a gene (ndk) for the presumably essential nucleoside diphosphate kinase (NDPK). We hypothesized that other activities might replace NDPK activity. We found in M. genitalium G37(T), Mycoplasma pneumoniae FH(T), Mycoplasma fermentans PG18(T), and Mycoplasma capricolum subsp. capricolum Kid(T) that their 6-phosphofructokinases (6-PFKs), phosphoglycerate kinases (PGKs), pyruvate kinases (PKs), and acetate kinases (AKs), besides reactant ADP/ATP, could use other ribo- and deoxyribo-purine and pyrimidine NDPs and NTPs. These activities could compensate for the absence of an orthologous ndk gene in the Mycoplasmataceae. They suggest a metabolically varied and consequential role for unrelated and perhaps unsuspected "replacement" or compensatory enzymes that may confound metabolic prediction. We partially purified and biochemically characterized the PKs, 6-PFKs, PGKs, and AKs from M. capricolum subsp. capricolum Kid(T) and M. fermentans PG18(T).

Cloning, expression, and characterization of acetate kinase from Lactobacillus sanfranciscensis

In the metabolism of Lactobacillus sanfranciscensis, the acetate kinase (AK) is a key enzyme and responsible for dephosphorylation of acetyl phosphate with the concomitant production of acetate and ATP. The L. sanfranciscensis ack gene was identified by PCR methods. It encodes a 397 amino acid protein sharing 56% similarity with Bacillus subtilis AK. Whereas cotranscription of ack and pta (phosphotransacetylase) is reported in previously characterised organisms, the L. sanfranciscensis ack gene is not located in direct neighbourhood to the encoding gene. AK was heterologously expressed in E. coli and characterised by its v(max) and Km values and by the dependence of enzyme activity on temperature and pH. Based on this data the in vivo role of the enzyme is discussed.

The role of histidines in the acetate kinase from Methanosarcina thermophila

The role of histidine in the catalytic mechanism of acetate kinase from Methanosarcina thermophila was investigated by diethylpyrocarbonate inactivation and site-directed mutagenesis. Inactivation was accompanied by an increase in absorbance at 240 nm with no change in absorbance at 280 nm, and treatment of the inactivated enzyme with hydroxylamine restored 95% activity, results that indicated diethylpyrocarbonate inactivates the enzyme by the specific modification of histidine. The substrates ATP, ADP, acetate, and acetyl phosphate protected against inactivation suggesting at least one active site where histidine is modified. Correlation of residual activity with the number of histidines modified, as determined by absorbance at 240 nm, indicated that a maximum of three histidines are modified per subunit, two of which are essential for full inactivation. Comparison of the M. thermophila acetate kinase sequence with 56 putative acetate kinase sequences revealed eight highly conserved histidines, three of which (His-123, His-180, and His-208) are perfectly conserved. Diethylpyrocarbonate inactivation of the eight histidine --> alanine variants indicated that His-180 and His-123 are in the active site and that the modification of both is necessary for full inactivation. Kinetic analyses of the eight variants showed that no other histidines are important for activity. Analysis of additional His-180 variants indicated that phosphorylation of His-180 is not essential for catalysis. Possible functions of His-180 are discussed.

Purification and characterization of two extremely thermostable enzymes, phosphate acetyltransferase and acetate kinase, from the hyperthermophilic eubacterium Thermotoga maritima

Phosphate acetyltransferase (PTA) and acetate kinase (AK) of the hyperthermophilic eubacterium Thermotoga maritima have been purified 1,500- and 250-fold, respectively, to apparent homogeneity. PTA had an apparent molecular mass of 170 kDa and was composed of one subunit with a molecular mass of 34 kDa, suggesting a homotetramer (alpha4) structure. The N-terminal amino acid sequence showed significant identity to that of phosphate butyryltransferases from Clostridium acetobutylicum rather than to those of known phosphate acetyltransferases. The kinetic constants of the reversible enzyme reaction (acetyl-CoA + Pi -->/<-- acetyl phosphate + CoA) were determined at the pH optimum of pH 6.5. The apparent Km values for acetyl-CoA, Pi, acetyl phosphate, and coenzyme A (CoA) were 23, 110, 24, and 30 microM, respectively; the apparent Vmax values (at 55 degrees C) were 260 U/mg (acetyl phosphate formation) and 570 U/mg (acetyl-CoA formation). In addition to acetyl-CoA (100%), the enzyme accepted propionyl-CoA (60%) and butyryl-CoA (30%). The enzyme had a temperature optimum at 90 degrees C and was not inactivated by heat upon incubation at 80 degrees C for more than 2 h. AK had an apparent molecular mass of 90 kDa and consisted of one 44-kDa subunit, indicating a homodimer (alpha2) structure. The N-terminal amino acid sequence showed significant similarity to those of all known acetate kinases from eubacteria as well that of the archaeon Methanosarcina thermophila. The kinetic constants of the reversible enzyme reaction (acetyl phosphate + ADP -->/<-- acetate + ATP) were determined at the pH optimum of pH 7.0. The apparent Km values for acetyl phosphate, ADP, acetate, and ATP were 0.44, 3, 40, and 0.7 mM, respectively; the apparent Vmax values (at 50 degrees C) were 2,600 U/mg (acetate formation) and 1,800 U/mg (acetyl phosphate formation). AK phosphorylated propionate (54%) in addition to acetate (100%) and used GTP (100%), ITP (163%), UTP (56%), and CTP (21%) as phosphoryl donors in addition to ATP (100%). Divalent cations were required for activity, with Mn2+ and Mg2+ being most effective. The enzyme had a temperature optimum at 90 degrees C and was stabilized against heat inactivation by salts. In the presence of (NH4)2SO4 (1 M), which was most effective, the enzyme did not lose activity upon incubation at 100 degrees C for 3 h. The temperature optimum at 90 degrees C and the high thermostability of both PTA and AK are in accordance with their physiological function under hyperthermophilic conditions.

Identification of essential glutamates in the acetate kinase from Methanosarcina thermophila

Acetate kinase catalyzes the reversible phosphorylation of acetate (CH3COO- + ATP<-->CH3CO2PO3(2-) + ADP). A mechanism which involves a covalent phosphoryl-enzyme intermediate has been proposed, and chemical modification studies of the enzyme from Escherichia coli indicate an unspecified glutamate residue is phosphorylated (J. A. Todhunter and D. L. Purich, Biochem. Biophys. Res. Commun. 60:273-280, 1974). Alignment of the amino acid sequences for the acetate kinases from E. coli (Bacteria domain), Methanosarcina thermophila (Archaea domain), and four other phylogenetically divergent microbes revealed high identity which included five glutamates. These glutamates were replaced in the M. thermophila enzyme to determine if any are essential for catalysis. The histidine-tagged altered enzymes were produced in E. coli and purified to electrophoretic homogeneity by metal affinity chromatography. Replacements of E384 resulted in either undetectable or extremely low kinase activity, suggesting E384 is essential for catalysis which supports the proposed mechanism. Replacement of E385 influenced the Km values for acetate and ATP with only moderate decreases in k(cat), which suggests that this residue is involved in substrate binding but not catalysis. The unaltered acetate kinase was not inactivated by N-ethylmaleimide; however, replacement of E385 with cysteine conferred sensitivity to N-ethylmaleimide which was prevented by preincubation with acetate, acetyl phosphate, ATP, or ADP, suggesting that E385 is located near the active site. Replacement of E97 decreased the Km value for acetate but not ATP, suggesting this residue is involved in binding acetate. Replacement of either E32 or E334 had no significant effects on the kinetic constants, which indicates that neither residue is essential for catalysis or significantly influences the binding of acetate or ATP.

Acetate kinase from Clostridium acetobutylicum: a highly specific enzyme that is actively transcribed during acidogenesis and solventogenesis

Acetate kinase (ATP:phosphotransferase, EC 2.7.2.1) has been purified 294-fold from acid-producing cells of Clostridium acetobutylicum DSM 1731 to a specific activity of 1087 U mg-1 (ADP-forming direction). The dimeric enzyme consisted of subunits with a molecular mass of 43 kDa. The molecular mass of the native acetate kinase was in the range 87-94 kDa as judged by gel filtration and native gel electrophoresis. The enzyme showed high specificity for the substrates acetate and ATP, and maximal activity was obtained with Mn2+ as divalent cation. The presence of mercury compounds such as HgCl2 and p-hydroxymercuribenzoate resulted in an essential loss of activity. The apparent K(m) values of acetate, Mg-ATP, acetyl phosphate, and Mg-ADP were 73, 0.37, 0.58 and 0.71 mM. An activity-staining procedure for detection of acetate kinase in crude cell extracts after separation on native polyacrylamide gels was developed. A DNA fragment encoding 246 bp of the acetate kinase gene of C. acetobutylicum DSM 792 was cloned by a PCR-based approach. Northern blot analysis revealed transcription of the gene under acid- and solvent-producing conditions with no significant differences at the level of transcription.

Cloning, sequence analysis, and hyperexpression of the genes encoding phosphotransacetylase and acetate kinase from Methanosarcina thermophila

The genes for the acetate-activating enzymes, acetate kinase and phosphotransacetylase (ack and pta), from Methanosarcina thermophila TM-1 were cloned and sequenced. Both genes are present in only one copy per genome, with the pta gene adjacent to and upstream of the ack gene. Consensus archaeal promoter sequences are found upstream of the pta coding region. The pta and ack genes encode predicted polypeptides with molecular masses of 35,198 and 44,482 Da, respectively. A hydropathy plot of the deduced phosphotransacetylase sequence indicates that it is a hydrophobic polypeptides; however, no membrane-spanning domains are evident. Comparison of the amino acid sequences deduced from the M. thermophila and Escherichia coli ack genes indicate similar subunit molecular weights and 44% identity (60% similarity). The comparison also revealed the presence of several conserved arginine, cysteine, and glutamic acid residues. Arginine, cysteine, and glutamic acid residues have previously been implicated at or near the active site of the E. coli acetate kinase. The pta and ack genes were hyperexpressed in E. coli, and the overproduced enzymes were purified to homogeneity with specific activities higher than those of the enzymes previously purified from M. thermophila. The overproduced phosphotransacetylase and acetate kinase migrated at molecular masses of 37,000 and 42,000 Da, respectively. The activity of the acetate kinase is optimal at 65 degrees C and is protected from thermal inactivation by ATP. Diethylpyrocarbonate and phenylglyoxal inhibited acetate kinase activity in a manner consistent with the presence of histidine and arginine residues at or near the active site; however, the thiol-directed reagents 5,5'-dithiobis (2-nitrobenzoic acid) and N-ethylmaleimide were ineffective.

The enzymatic synthesis of membrane glucolipids in Acholeplasma laidlawii

In membranes of the prokaryote Acholeplasma laidlawii, the physiological regulation of the two major membrane lipids, monoglucosyldiacylglycerol (MGlcDAG) and diglucosyldiacylglycerol (DGlcDAG), is governed by factors affecting the equilibria between lamellar and non-lamellar phases of the membrane lipids. The synthesis of the glucolipids is considered to be a two-step glucosylation: (i) DAG+UDP-Glc----MGlcDAG+UDP; and (ii) MGlcDAG+UDP-Glc----DGlcDAG+UPD. This was corroborated by in vivo pulse labelling experiments showing turnover of MGlcDAG but not DGlcDAG. The enzymatic synthesis of MGlcDAG was localized to fresh or freeze-dried membranes in vitro. Synthesis of DGlcDAG was minor in such membranes but of substantial magnitude in intact cells. Synthesis of MGlcDAG was stimulated by small amounts of SDS but completely inhibited upon solubilization of the membranes by a variety of detergents. The inhibitory effect of several UDP-Glc analogs on glucolipid synthesis demonstrated the importance of UDP-Glc as the sugar donor. Synthesis of both glucolipids was lost in freeze-dried plus lipid-extracted cells but restored when lipids were transferred back to the extracted cell membrane. By selectively adding specific lipids, a strong dependence on the acceptor lipid DAG, as well as the need for general matrix lipids for enzyme activity, was established. In addition, the anionic phosphatidylglycerol (PG), but not the other phospholipids, had a strong stimulatory effect. The presence of different phosphorylating agents stimulated the synthesis of DGlcDAG and partially inhibited that of MGlcDAG. This, together with the lipid dependency, may constitute mechanisms for the regulation of the enzyme activities in vivo.

Properties of acetate kinase isozymes and a branched-chain fatty acid kinase from a spirochete

Spirochete MA-2, which is anaerobic, ferments glucose, forming acetate as a major product. The spirochete also ferments (but does not utilize as growth substrates) small amounts of l-leucine, l-isoleucine, and l-valine, forming the branched-chain fatty acids isovalerate, 2-methylbutyrate, and isobutyrate, respectively, as end products. Energy generated through the fermentation of these amino acids is utilized to prolong cell survival under conditions of growth substrate starvation. A branched-chain fatty acid kinase and two acetate kinase isozymes were resolved from spirochete MA-2 cell extracts. Kinase activity was followed by measuring the formation of acyl phosphate from fatty acid and ATP. The branched-chain fatty acid kinase was active with isobutyrate, 2-methylbutyrate, isovalerate, butyrate, valerate, or propionate as a substrate but not with acetate as a substrate. The acetate kinase isozymes were active with acetate and propionate as substrates but not with longer-chain fatty acids as substrates. The acetate kinase isozymes and the branched-chain fatty acid kinase differed in nucleoside triphosphate and cation specificities. Each acetate kinase isozyme had an apparent molecular weight of approximately 125,000, whereas the branched-chain fatty acid kinase had a molecular weight of approximately 76,000. These results show that spirochete MA-2 synthesizes a branched-chain fatty acid kinase specific for leucine, isoleucine, and valine fermentation. It is likely that a phosphate branched-chain amino acids is also synthesized by spirochete MA-2. Thus, in spirochete MA-2, physiological mechanisms have evolved which serve specifically to generate maintenance energy from branched-chain amino acids.

Acetate kinase activity in mycoplasmas

Acetate kinase activity was assayed in 13 mycoplasmas. Nine species exhibited the enzymic activity in the direction of either synthesis of acetylphosphate or adenosine triphosphate. On the other hand Mycoplasma orale, Mycoplasma arthritidis, Ureaplasma urealyticum (10 serotypes), and two strains of Anaeroplasma species exhibited only minimal levels of the enzymic activity. In these four species, the enzyme does not seem to play a key role in adenosine triphosphate formation.

Energy metabolism in Capnocytophaga ochracea

Among the microflora of the gingival sulcus are members of the genus Capnocytophaga which have been implicated as possible etiological agents of juvenile periodontitis and systemic infectious diseases. In this study, the pathway used by C. ochracea strain 25 for generating energy from glucose was investigated. When grown in a complex medium supplemented with glucose and NaHCO(3), the major end products formed were acetate (4.6 mmol), succinate (11.0 mmol), pyruvate (4.3 mmol), and oxalacetate (3.6 mmol), and the molar growth yield was 58. Addition of yeast extract to the growth medium caused (i) an increase in acetate (9.2 mmol) and succinate (14.3 mmol), (ii) a decrease in pyruvate (0 mmol) and oxalacetate (1.1 mmol), and (iii) the molar growth yield increased to 75. Glucose was transported by a phosphoenolpyruvate:phosphotransferase system and then catabolized to phosphoenolpyruvate by enzymes of the Embden-Meyerhof-Parnas pathway. No activities were detected for the key enzymes of the Warburg-Dickens, Entner-Douderoff, or hexose phosphoketolase pathways. During growth in the yeast extract-supplemented medium, approximately 37% of the phosphoenolpyruvate carbon was converted to acetate by pyruvate kinase, a pyruvate-decarboxylating enzyme activity, and acetate kinase; the remaining 63% was converted to succinate via phosphoenolpyruvate carboxykinase, malate dehydrogenase, fumarate hydratase, and fumarate reductase.

Acetate kinase in the genus Veillonella: effect of succinate, serological cross-reactivity, and separation by electrophoresis

Acetate kinases from the genus Veillonella were divided into two types: a succinate-stimulated enzyme and a succinate-independent enzyme. Three strains, V. parvula ATCC 17743 (antigenic group II), V. parvula ATCC 17744 (V), and V. parvula ATCC 10790 (VI), contained the succinate-stimulated enzyme. Among four types strains of V. alcalescens, three strains, ATCC 17747 (I), ATCC 17746 (III), and ATCC 17748 (VII), contained the succinate-independent enzyme, whereas only one strain, ATCC 17745 (IV), contained the succinate-stimulated enzyme. Small amounts of antiserum to the purified acetate kinase from V. alcalescens ATCC 17748 completely inhibited the purified and crude enzyme activity from the strain. Classification of the enzymes on the basis of stimulation by succinate was consistent with classification based on serological reactions using the antiserum as an independent parameter. The succinate-stimulated enzyme could be separated into two classes according to the degree of sensitivity to succinate: (i) enzymes from V. parvula ATCC 17744 and V. alcalescens ATCC 17745, which could be demonstrated on gel after electrophoresis by a histochemical method to be highly stimulated by the presence of succinate in the reaction mixture, and (ii) enzymes from V. parvula ATCC 10790 and V. parvula ATCC 17743, which could be easily demonstrated without succinate. Four groups of acetate kinases from the genus Veillonella were separated by gel electrophoretic mobility. The results showed that almost all enzymes from the seven type strains were heterogeneous at the molecular level.