Expression, purification and characterization of the acyl carrier protein phosphodiesterase from Pseudomonas Aeruginosa

Identification, Evolutionary Dynamics, and Gene Expression Patterns of the ACP Gene Family in Responding to Salt Stress in Brassica Genus

Acyl carrier proteins (ACPs) have been reported to play a crucial role in responding to biotic and abiotic stresses, regulating growth and development. However, the biological function of the ACP gene family in the Brassica genus has been limited until now. In this study, we conducted a comprehensive analysis and identified a total of 120 ACP genes across six species in the Brassica genus. Among these, there were 27, 26, and 30 ACP genes in the allotetraploid B. napus, B. juncea, and B. carinata, respectively, and 14, 13, and 10 ACP genes in the diploid B. rapa, B. oleracea, and B. nigra, respectively. These ACP genes were further classified into six subclades, each containing conserved motifs and domains. Interestingly, the majority of ACP genes exhibited high conservation among the six species, suggesting that the genome evolution and polyploidization processes had relatively minor effects on the ACP gene family. The duplication modes of the six Brassica species were diverse, and the expansion of most ACPs in Brassica occurred primarily through dispersed duplication (DSD) events. Furthermore, most of the ACP genes were under purifying selection during the process of evolution. Subcellular localization experiments demonstrated that ACP genes in Brassica species are localized in chloroplasts and mitochondria. Cis-acting element analysis revealed that most of the ACP genes were associated with various abiotic stresses. Additionally, RNA-seq data revealed differential expression levels of BnaACP genes across various tissues in B. napus, with particularly high expression in seeds and buds. qRT-PCR analysis further indicated that BnaACP genes play a significant role in salt stress tolerance. These findings provide a comprehensive understanding of ACP genes in Brassica plants and will facilitate further functional analysis of these genes.

Dinoflagellate Phosphopantetheinyl Transferase (PPTase) and Thiolation Domain Interactions Characterized Using a Modified Indigoidine Synthesizing Reporter

Photosynthetic dinoflagellates synthesize many toxic but also potential therapeutic compounds therapeutics via polyketide/non-ribosomal peptide synthesis, a common means of producing natural products in bacteria and fungi. Although canonical genes are identifiable in dinoflagellate transcriptomes, the biosynthetic pathways are obfuscated by high copy numbers and fractured synteny. This study focuses on the carrier domains that scaffold natural product synthesis (thiolation domains) and the phosphopantetheinyl transferases (PPTases) that thiolate these carriers. We replaced the thiolation domain of the indigoidine producing BpsA gene from Streptomyces lavendulae with those of three multidomain dinoflagellate transcripts and coexpressed these constructs with each of three dinoflagellate PPTases looking for specific pairings that would identify distinct pathways. Surprisingly, all three PPTases were able to activate all the thiolation domains from one transcript, although with differing levels of indigoidine produced, demonstrating an unusual lack of specificity. Unfortunately, constructs with the remaining thiolation domains produced almost no indigoidine and the thiolation domain for lipid synthesis could not be expressed in E. coli. These results combined with inconsistent protein expression for different PPTase/thiolation domain pairings present technical hurdles for future work. Despite these challenges, expression of catalytically active dinoflagellate proteins in E. coli is a novel and useful tool going forward.

Characterization of Phosphopantetheinyl Hydrolase from Mycobacterium tuberculosis

Phosphopantetheinyl hydrolase, PptH (Rv2795c), is a recently discovered enzyme from Mycobacterium tuberculosis that removes 4'-phosphopantetheine (Ppt) from holo-carrier proteins (CPs) and thereby opposes the action of phosphopantetheinyl transferases (PPTases). PptH is the first structurally characterized enzyme of the phosphopantetheinyl hydrolase family. However, conditions for optimal activity of PptH have not been defined, and only one substrate has been identified. Here, we provide biochemical characterization of PptH and demonstrate that the enzyme hydrolyzes Ppt in vitro from more than one M. tuberculosis holo-CP as well as holo-CPs from other organisms. PptH provided the only detectable activity in mycobacterial lysates that dephosphopantetheinylated acyl carrier protein M (AcpM), suggesting that PptH is the main Ppt hydrolase in M. tuberculosis. We could not detect a role for PptH in coenzyme A (CoA) salvage, and PptH was not required for virulence of M. tuberculosis during infection of mice. It remains to be determined why mycobacteria conserve a broadly acting phosphohydrolase that removes the Ppt prosthetic group from essential CPs. We speculate that the enzyme is critical for aspects of the life cycle of M. tuberculosis that are not routinely modeled. IMPORTANCE Tuberculosis (TB), caused by Mycobacterium tuberculosis, was the leading cause of death from an infectious disease before COVID, yet the in vivo essentiality and function of many of the protein-encoding genes expressed by M. tuberculosis are not known. We biochemically characterize M. tuberculosis's phosphopantetheinyl hydrolase, PptH, a protein unique to mycobacteria that removes an essential posttranslational modification on proteins involved in synthesis of lipids important for the bacterium's cell wall and virulence. We demonstrate that the enzyme has broad substrate specificity, but it does not appear to have a role in coenzyme A (CoA) salvage or virulence in a mouse model of TB.

The biosynthetic pathway to tetromadurin (SF2487/A80577), a polyether tetronate antibiotic

The type I polyketide SF2487/A80577 (herein referred to as tetromadurin) is a polyether tetronate ionophore antibiotic produced by the terrestrial Gram-positive bacterium Actinomadura verrucosospora. Tetromadurin is closely related to the polyether tetronates tetronasin (M139603) and tetronomycin, all of which are characterised by containing a tetronate, cyclohexane, tetrahydropyran, and at least one tetrahydrofuran ring. We have sequenced the genome of Actinomadura verrucosospora to identify the biosynthetic gene cluster responsible for tetromadurin biosynthesis (the mad gene cluster). Based on bioinformatic analysis of the 32 genes present within the cluster a plausible biosynthetic pathway for tetromadurin biosynthesis is proposed. Functional confirmation of the mad gene cluster is obtained by performing in-frame deletions in each of the genes mad10 and mad31, which encode putative cyclase enzymes responsible for cyclohexane and tetrahydropyran formation, respectively. Furthermore, the A. verrucosospora Δmad10 mutant produces a novel tetromadurin metabolite that according to mass spectrometry analysis is analogous to the recently characterised partially cyclised tetronasin intermediate lacking its cyclohexane and tetrahydropyran rings. Our results therefore elucidate the biosynthetic machinery of tetromadurin biosynthesis and lend support for a conserved mechanism of cyclohexane and tetrahydropyran biosynthesis across polyether tetronates.

Quantifying protein-protein interactions of the acyl carrier protein with solvatochromic probes

Protein-protein interactions (PPIs) are universal to life and their study and understanding is critical to drug discovery and bioengineering efforts. Historically, X-ray crystallography, isothermal titration calorimetry and other biophysical methods have been used to study PPIs, but can be costly and are low throughput, hindering progress towards rapid evaluation of these interactions. Recent interest in targeting PPIs and in engineering biosynthetic pathways in which PPIs play a critical role has driven innovation in their evaluation but a universal screen is still needed. One of the best characterized systems relying upon PPIs is Escherichia coli type II fatty acid biosynthesis in which the central acyl carrier protein (EcACP) shuttles substrates to a series of partner enzymes. Here we present a method by which EcACP is labeled with a solvatochromic dye, 4-DMN, and then allowed to interact with its various partner enzymes. Upon interaction, there is a large increase in fluorescence intensity which is easily monitored via fluorometer or plate reader. This method is useful in the study of known PPI, hypothetical PPI and in evaluation of inhibitors of both partner enzyme active site and of the PPI itself.

Structural insights into phosphopantetheinyl hydrolase PptH from Mycobacterium tuberculosis

The amidinourea 8918 was recently reported to inhibit the type II phosphopantetheinyl transferase (PPTase) of Mycobacterium tuberculosis (Mtb), PptT, a potential drug-target that activates synthases and synthetases involved in cell wall biosynthesis and secondary metabolism. Surprisingly, high-level resistance to 8918 occurred in Mtb harboring mutations within the gene adjacent to pptT, rv2795c, highlighting the role of the encoded protein as a potentiator of the bactericidal action of the amidinourea. Those studies revealed that Rv2795c (PptH) is a phosphopantetheinyl (PpT) hydrolase, possessing activity antagonistic with respect to PptT. We have solved the crystal structure of Mtb's phosphopantetheinyl hydrolase, making it the first phosphopantetheinyl (carrier protein) hydrolase structurally characterized. The 2.5 Å structure revealed the hydrolases' four-layer (α/β/β/α) sandwich fold featuring a Mn-Fe binuclear center within the active site. A structural similarity search confirmed that PptH most closely resembles previously characterized metallophosphoesterases (MPEs), particularly within the vicinity of the active site, suggesting that it may utilize a similar catalytic mechanism. In addition, analysis of the structure has allowed for the rationalization of the previously reported PptH mutations associated with 8918-resistance. Notably, differences in the sequences and predicted structural characteristics of the PpT hydrolases PptH of Mtb and E. coli's acyl carrier protein hydrolase (AcpH) indicate that the two enzymes evolved convergently and therefore are representative of two distinct PpT hydrolase families.

Opposing reactions in coenzyme A metabolism sensitize Mycobacterium tuberculosis to enzyme inhibition

Mycobacterium tuberculosis (Mtb) is the leading infectious cause of death in humans. Synthesis of lipids critical for Mtb's cell wall and virulence depends on phosphopantetheinyl transferase (PptT), an enzyme that transfers 4'-phosphopantetheine (Ppt) from coenzyme A (CoA) to diverse acyl carrier proteins. We identified a compound that kills Mtb by binding and partially inhibiting PptT. Killing of Mtb by the compound is potentiated by another enzyme encoded in the same operon, Ppt hydrolase (PptH), that undoes the PptT reaction. Thus, loss-of-function mutants of PptH displayed antimicrobial resistance. Our PptT-inhibitor cocrystal structure may aid further development of antimycobacterial agents against this long-sought target. The opposing reactions of PptT and PptH uncover a regulatory pathway in CoA physiology.

Only Acyl Carrier Protein 1 (AcpP1) Functions in Pseudomonas aeruginosa Fatty Acid Synthesis

The genome of Pseudomonas aeruginosa contains three open reading frames, PA2966, PA1869, and PA3334, which encode putative acyl carrier proteins, AcpP1, AcpP2, and AcpP3, respectively. In this study, we found that, although these apo-ACPs were successfully phosphopantetheinylated by P. aeruginosa phosphopantetheinyl transferase (PcpS) and all holo-forms of these proteins could be acylated by Vibrio harveyi acyl-ACP synthetase (AasS), only AcpP1 could be used as a substrate for the synthesis of fatty acids, catalyzed by P. aeruginosa cell free extracts in vitro, and only acpP1 gene could restore growth in the Escherichia coliacpP mutant strain CY1877. And P. aeruginosaacpP1 could not be deleted, while disruption of acpP2 or acpP3 in the P. aeruginosa genome allowed mutant strains to grow as well as the wild type strain. These findings confirmed that only P. aeruginosa AcpP1 functions in fatty acid biosynthesis, and that acpP2 and acpP3 do not play roles in the fatty acid synthetic pathway. Moreover, disruption of acpP2 and acpP3 did not affect the ability of P. aeruginosa to produce N-acylhomoserine lactones (AHL), but replacement of P. aeruginosaacpP1 with E. coliacpP caused P. aeruginosa to reduce the production of AHL molecules, which indicated that neither P. aeruginosa AcpP2 nor AcpP3 can act as a substrate for synthesis of AHL molecules in vivo. Furthermore, replacement of acpP1 with E. coliacpP reduced the ability of P. aeruginosa to produce some exo-products and abolished swarming motility in P. aeruginosa.

Acyl hydrolases from trans-AT polyketide synthases target acetyl units on acyl carrier proteins

Acyl hydrolase (AH) domains are a common feature of trans-AT PKSs. They have been hypothesised to perform a proofreading function by removing acyl chains from stalled sites. This study determines the substrate tolerance of the AH PedC for a range of acyl-ACPs. Clear preference towards short, linear acyl-ACPs is shown, with acetyl-ACP the best substrate. These results imply a more targeted housekeeping role for PedC: namely the removal of unwanted acetyl groups from ACP domains caused by erroneous transfer of acetyl-CoA, or possibly by decarboxylation of malonyl-ACP.

Using modern tools to probe the structure-function relationship of fatty acid synthases

Fatty acid biosynthesis is essential to life and represents one of the most conserved pathways in nature, preserving the same handful of chemical reactions across all species. Recent interest in the molecular details of the de novo fatty acid synthase (FAS) has been heightened by demand for renewable fuels and the emergence of multidrug-resistant bacterial strains. Central to FAS is the acyl carrier protein (ACP), a protein chaperone that shuttles the growing acyl chain between catalytic enzymes within the FAS. Human efforts to alter fatty acid biosynthesis for oil production, chemical feedstock, or antimicrobial purposes has been met with limited success, due in part to a lack of detailed molecular information behind the ACP-partner protein interactions inherent to the pathway. This review will focus on recently developed tools for the modification of ACP and analysis of protein-protein interactions, such as mechanism-based crosslinking, and the studies exploiting them. Discussion specific to each enzymatic domain will focus first on mechanism and known inhibitors, followed by available structures and known interactions with ACP. Although significant unknowns remain, new understandings of the intricacies of FAS point to future advances in manipulating this complex molecular factory.

Fatty acid biosynthesis revisited: structure elucidation and metabolic engineering

Fatty acids are primary metabolites synthesized by complex, elegant, and essential biosynthetic machinery. Fatty acid synthases resemble an iterative assembly line, with an acyl carrier protein conveying the growing fatty acid to necessary enzymatic domains for modification. Each catalytic domain is a unique enzyme spanning a wide range of folds and structures. Although they harbor the same enzymatic activities, two different types of fatty acid synthase architectures are observed in nature. During recent years, strained petroleum supplies have driven interest in engineering organisms to either produce more fatty acids or specific high value products. Such efforts require a fundamental understanding of the enzymatic activities and regulation of fatty acid synthases. Despite more than one hundred years of research, we continue to learn new lessons about fatty acid synthases' many intricate structural and regulatory elements. In this review, we summarize each enzymatic domain and discuss efforts to engineer fatty acid synthases, providing some clues to important challenges and opportunities in the field.

Chemoenzymatic exchange of phosphopantetheine on protein and peptide

Evaluation of new acyl carrier protein hydrolase (AcpH, EC 3.1.4.14) homologs from proteobacteria and cyanobacteria reveals significant variation in substrate selectivity and kinetic parameters for phosphopantetheine hydrolysis from carrier proteins. Evaluation with carrier proteins from both primary and secondary metabolic pathways reveals an overall preference for acyl carrier protein (ACP) substrates from type II fatty acid synthases, as well as variable activity for polyketide synthase ACPs and peptidyl carrier proteins (PCP) from non-ribosomal peptide synthases. We also demonstrate the kinetic parameters of these homologs for AcpP and the 11-mer peptide substrate YbbR. These findings enable the fully reversible labeling of all three classes of natural product synthase carrier proteins as well as full and minimal fusion protein constructs.

Resin supported acyl carrier protein labeling strategies

The post-translational modifying enzymes phophopantetheinyl transferase and acyl carrier protein hydrolase have shown utility in the functional modification of acyl carrier proteins. Here we develop these tools as immobilized biocatalysts on agarose supports. New utility is imparted through these methods, enabling rapid and label-independent protein purification. Immobilization of acyl carrier protein is also demonstrated for rapid activity assays of these 4'-phosophopantetheine modifying enzymes, displaying a particular advantage in the case of phosphopantetheine removal, where few orthogonal techniques have been demonstrated. These tools further enrich the suite of functional utility of 4'-phosophopantetheine chemistry, with applications to protein functionalization, materials, and natural product biosynthetic studies.

The phosphopantetheinyl transferases: catalysis of a post-translational modification crucial for life

Covering: up to 2013. Although holo-acyl carrier protein synthase, AcpS, a phosphopantetheinyl transferase (PPTase), was characterized in the 1960s, it was not until the publication of the landmark paper by Lambalot et al. in 1996 that PPTases garnered wide-spread attention being classified as a distinct enzyme superfamily. In the past two decades an increasing number of papers have been published on PPTases ranging from identification, characterization, structure determination, mutagenesis, inhibition, and engineering in synthetic biology. In this review, we comprehensively discuss all current knowledge on this class of enzymes that post-translationally install a 4'-phosphopantetheine arm on various carrier proteins.

Reversible labeling of native and fusion-protein motifs

The reversible covalent attachment of chemical probes to proteins has long been sought as a means to visualize and manipulate proteins. Here we demonstrate the full reversibility of post-translational custom pantetheine modification of Escherichia coli acyl carrier protein for visualization and functional studies. We use this iterative enzymatic methodology in vitro to reversibly label acyl carrier protein variants and apply these tools to NMR structural studies of protein-substrate interactions.

Manipulating fatty acid biosynthesis in microalgae for biofuel through protein-protein interactions

Microalgae are a promising feedstock for renewable fuels, and algal metabolic engineering can lead to crop improvement, thus accelerating the development of commercially viable biodiesel production from algae biomass. We demonstrate that protein-protein interactions between the fatty acid acyl carrier protein (ACP) and thioesterase (TE) govern fatty acid hydrolysis within the algal chloroplast. Using green microalga Chlamydomonas reinhardtii (Cr) as a model, a structural simulation of docking CrACP to CrTE identifies a protein-protein recognition surface between the two domains. A virtual screen reveals plant TEs with similar in silico binding to CrACP. Employing an activity-based crosslinking probe designed to selectively trap transient protein-protein interactions between the TE and ACP, we demonstrate in vitro that CrTE must functionally interact with CrACP to release fatty acids, while TEs of vascular plants show no mechanistic crosslinking to CrACP. This is recapitulated in vivo, where overproduction of the endogenous CrTE increased levels of short-chain fatty acids and engineering plant TEs into the C. reinhardtii chloroplast did not alter the fatty acid profile. These findings highlight the critical role of protein-protein interactions in manipulating fatty acid biosynthesis for algae biofuel engineering as illuminated by activity-based probes.

Solution structures of the acyl carrier protein domain from the highly reducing type I iterative polyketide synthase CalE8

Biosynthesis of the enediyne natural product calicheamicins γ₁^I in Micromonospora echinospora ssp. calichensis is initiated by the iterative polyketide synthase (PKS) CalE8. Recent studies showed that CalE8 produces highly conjugated polyenes as potential biosynthetic intermediates and thus belongs to a family of highly-reducing (HR) type I iterative PKSs. We have determined the NMR structure of the ACP domain (meACP) of CalE8, which represents the first structure of a HR type I iterative PKS ACP domain. Featured by a distinct hydrophobic patch and a glutamate-residue rich acidic patch, meACP adopts a twisted three-helix bundle structure rather than the canonical four-helix bundle structure. The so-called ‘recognition helix’ (α2) of meACP is less negatively charged than the typical type II ACPs. Although loop-2 exhibits greater conformational mobility than other regions of the protein with a missing short helix that can be observed in most ACPs, two bulky non-polar residues (Met⁹⁹², Phe⁹⁹⁶) from loop-2 packed against the hydrophobic protein core seem to restrict large movement of the loop and impede the opening of the hydrophobic pocket for sequestering the acyl chains. NMR studies of the hydroxybutyryl- and octanoyl-meACP confirm that meACP is unable to sequester the hydrophobic chains in a well-defined central cavity. Instead, meACP seems to interact with the octanoyl tail through a distinct hydrophobic patch without involving large conformational change of loop-2. NMR titration study of the interaction between meACP and the cognate thioesterase partner CalE7 further suggests that their interaction is likely through the binding of CalE7 to the meACP-tethered polyene moiety rather than direct specific protein-protein interaction.

2',3'-cAMP hydrolysis by metal-dependent phosphodiesterases containing DHH, EAL, and HD domains is non-specific: Implications for PDE screening

The recent report of 2',3'-cAMP isolated from rat kidney is the first proof of its biological existence, which revived interest in this mysterious molecule. 2',3'-cAMP serves as an extracellular adenosine source, but how it is degraded remains unclear. Here, we report that 2',3'-cAMP can be hydrolyzed by six phosphodiesterases containing three different families of hydrolytic domains, generating invariably 3'-AMP but not 2'-AMP. The catalytic efficiency (k(cat)/K(m)) of each enzyme against 2',3'-cAMP correlates with that against the widely used non-specific substrate bis(p-nitrophenyl)phosphate (bis-pNPP), indicating that 2',3'-cAMP is a previously unknown non-specific substrate for PDEs. Furthermore, we show that the exclusive formation of 3'-AMP is due to the P-O2' bond having lower activation energy and is not the result of steric exclusion at enzyme active site. Our analysis provides mechanistic basis to dissect protein function when 2',3'-cAMP hydrolysis is observed.