Localization of acyl carrier protein in Escherichia coli.

Acyl carrier protein was localized by immunoelectron microscopy in the cytoplasm of Escherichia coli. These data are inconsistent with the previous report of an association between acyl carrier protein and the inner membrane (H. Van den Bosch, J.R. Williamson, and P.R. Vagelos, Nature [London] 228:338-341, 1970). Moreover, bacterial membranes did not bind a significant amount of acyl carrier protein or its thioesters in vitro. A thioesterase activity specific for long-chain acyl-acyl carrier protein was associated with the inner membrane.     

Membrane-binding sites for acyl carrier protein in Escherichia coli

We report that membrane vesicles of Escherichia coli contain protein-binding sites for acyl carrier protein. Scatchard analysis of the binding indicates a dissociation constant around 0.35 micrometers and a maximum number of protein-binding sites around 50 pmol per mg of membrane protein. Binding is on the inner membrane while the outer membrane is devoid of binding sites. These results are consistent with the fact that some acyl carrier protein-dependent enzymes implicated in phospholipid- and membrane-derived oligosaccharide biosynthesis are localized in the cytoplasmic membrane.     

Photoaffinity cross-linking of acyl carrier protein to Escherichia coli membranes.

Acyl Carrier Protein (ACP) is a small acidic protein which interacts with the various enzymes implicated in the biosynthesis of fatty acids in E. coli. It also interacts with the inner membrane proteins implicated in the biosynthesis of phospholipids. Samples of radioactive ACP were prepared with high specific activities and bearing photoactivable aryl azide derivatives. Two photoactivable reagents were used: para azido phenacyl bromide (pAPA) which reacts with the SH of the ACP prosthetic group and the N-hydroxysuccinimide ester of 4-azido salicylic acid (NHS-ASA) which reacts with the amino groups of the protein. Various methods were used to demonstrate that ACP could be cross-linked specifically to an inner membrane protein of E. coli, most probably to the glycerol-3-phosphate acyl transferase (GPAT). This covalent link should provide a powerful tool for further analysis of the structure of GPAT and its role in phospholipid biosynthesis. These photoactivable aryl azide derivatives of ACP could also be very useful for studying the interaction of ACP with the soluble enzymes implicated in fatty acid biosynthesis.     

Structural homology of spinach acyl carrier protein and Escherichia coli acyl carrier protein based on NMR data

Acyl carrier proteins (ACPs) from spinach and from Escherichia coli have been used to demonstrate the utility of proton NMR for comparison of homologous structures. The structure of E. coli ACP had been previously determined and modeled as a rapid equilibrium among multiple conformational forms (Kim and Prestegard, Biochemistry 28:8792–8797, 1989). Spinach ACP showed two slowly exchanging forms and could be manipulated into one form for structural study. Here we compare this single form to postulated multiple forms of E. coli ACP using the limited amount of NOE data available for the spinach protein. A number of long-range NOE contacts were present between homologous residues in both spinach and E. coli ACP, suggesting tertiary structural homology. To allow a more definitive structural comparison, a method was developed to use spinach ACP NOE constraints to search for regions of structural divergence from two postulated forms of E. coli ACP. The homologous regions of the two protein sequences were aligned, additional distance constraints were extracted from the E. coli structure, and these were mapped onto the spinach sequence. These distance constraints were combined with experimental NOE constraints and a distance geometry simulated annealing protocol was used to test for compatibility of the constraints. All of the experimental spinach NOE constraints could be successfully combined with the E. coli data, confirming the general hypothesis of structural homology. A better fit was obtained with one form, suggesting a preferential stabilization of that form in the spinach case. Proteins 27:131–143 © 1997 Wiley-Liss, Inc.     

On the structure-function relationship of acyl carrier protein of Escherichia coli.

The conformations of Escherichia coli acyl carrier protein (ACP) and acetylated ACP have been studied as a function of pH and salt concentration by circular dichroism measurements. The results show that the amino groups of ACP in their protonated form are important for maintaining the native conformation of the protein at physiological pH. However, externally added cations (divalent more effectively than monovalent ones) can substitute for the ammonium groups in maintaining the ordered structure pf ACP. It is suggested that both the ammonium groups of ACP and externally added cations reduce the repulsion between carboxylate groups of ACP and thereby prevent the unfolding of the protein. A reduction of the number of negatively charged carboxylate groups by either protonation or chemical modification abolished the requirement for either ammonium groups or other cations. A qualitative agreement between the effect of salt on the conformation and on the biological activity of acetylated ACP has been observed. The single arginine residue of acetylated ACP has been modified by treatment with a trimer of 2,3-butanedione with the resulting derivative of ACP retaining most of its biological activity.     

Isolation and properties of acyl carrier protein phosphodiesterase of Escherichia coli.

The acyl carrier protein (ACP) phosphodiesterase of Escherichia coli catalyzes the hydrolytic cleavage of the 4'-phosphopantetheine residue from ACP, with the generation of apo-ACP (P. R. Vagelos and A. R. Larrabee, J. Biol. Chem. 242:1776-1781, 1967). Although it has been postulated to play a role in the regulation of fatty acid synthesis, presently available evidence makes this unlikely, and its physiological function requires further investigation. We have now purified the enzyme from E. coli more than 3,000-fold and have identified it as a protein of Mr 25,000, as judged from its migration during electrophoresis in gels containing sodium dodecyl sulfate. The enzyme has remarkable thermostability, being protected against irreversible inactivation at 90 degrees C by the presence of sodium dodecyl sulfate. A partial sequence of the amino terminus of the enzyme is as follows: H2N-Ser-Lys-Val-Leu-Val-Leu-Lys-Ser-?-Ile-Leu-Ala-Gly-Tyr-Ser-. Other properties of the enzyme are also described.     

大肠杆菌holo-ACP的过表达、分离纯化及长链脂酰ACP的合成

[目的]获得高纯度大肠杆菌holo-ACP和多种长链脂酰ACP,为研究细菌脂肪酸、类脂A和N-酯酰高丝氨酸内脂等物质的合成提供底物.[方法和结果]采用PCR方法扩增得到大肠杆菌酰基载体蛋白基因(acpP)和holo-ACP合成酶基因(acpS).使用载体pBAD24、pBAD34和pET28b分别克隆了acpP和acpS,得到pBAD-ACP、pET-ACP和pET-ACP-ACPS 3个ACP表达质粒和一个AcpS表达质粒pBAD-ACPS.分别用3个ACP表达质粒转化大肠杆菌DH5a和BL21(DE3),构建了DH5αpBAD-ACP、BL21(DE3)/pET-ACP和BL21(DE3)/pET-ACP-ACPS 3种ACP生产菌株.与holo-ACP纯化常用菌株DK574相比,虽然三菌株在诱导时均能过量表达ACP,但是holo-ACP所占比例偏低.为了提高ACP生产菌株holo-ACP的产量,用质粒pBAD-ACPS分别转化上述3种ACP生产菌株,获得了3种携带双质粒的ACP生产菌株.表达结果显示携带pBAD-ACP和pBAD-ACPS双质粒的DH5a菌株比DK574菌株能产生更多的holo-ACP,且纯度也得到提高(纯度达99%).同时使用UNOsphere Q阴离子交换层析从这一菌株培养物中分离纯化到了高纯度的holo-ACP,并以纯化到的holo-ACP和多种长链脂肪酸为底物在哈氏弧菌脂酰ACP合成酶的催化下,合成了多种长链脂酰ACP.[结论]通过研究获得一株holo-ACP高产菌株,并证明在大肠杆菌菌株中,同时表达acpP基因和acpS基因,有利于holo-ACP的产生.     

Resin-based investigation of acyl carrier protein interaction networks in Escherichia coli

Protein-protein interactions play an integral role in metabolic regulation. Elucidation of these networks is complicated by the changing identity of the proteins themselves. Here we demonstrate a resin-based technique that leverages the unique tools for acyl carrier protein (ACP) modification with non-hydrolyzable linkages. ACPs from Escherichia coli and Shewanella oneidensis MR-1 are bound to Affigel-15 with varying acyl groups attached and introduced to proteomic samples. Isolation of these binding partners is followed by MudPIT analysis to identify each interactome with the variable of ACP-tethered substrates. These techniques allow for investigation of protein interaction networks with the changing identity of a given protein target.     

Preliminary X-ray diffraction studies of acyl carrier protein from Escherichia coli

Crystals of the acyl carrier protein of Escherichia coli have been grown and analyzed by X-ray diffraction. The crystals grow in space group C2 with unit cell dimensions a = 46.8 A, b = 52.1 A, c = 47.3 A and beta = 93.2 degrees. An isomorphous derivative, HgCl2, has been identified and characterized.     

Chemical and posttranslational modification of Escherichia coli acyl carrier protein for preparation of dansyl-acyl carrier proteins

Escherichia coli acyl carrier protein (ACP) contains a single tyrosine residue at position 71. The combined o-nitration of apo-ACP Y71 by tetranitromethane and reduction to 3-aminotyrosyl-apo-ACP were performed to introduce a specific site for attachment of a dansyl fluorescent label. Conditions for purification and characterization of dansylaminotyrosyl-apo-ACP are reported. Dansylaminotyrosyl-apo-ACP was enzymatically phosphopantetheinylated and acylated in vitro with an overall approximately 30% yield of purified stearoyl-dansylaminotyrosyl-ACP starting from unmodified apo-ACP. The steady-state kinetic parameters k(cat) = 22 min(-1) and K(M) = 2.7 microM were determined for reaction of stearoyl-dansylaminotyrosyl-ACP with stearoyl-ACP Delta(9)-desaturase. These results show that dansylaminotyrosyl-ACP will function well for studying binding interactions with the Delta(9)-desaturase and suggest similar possibilities for other ACP-dependent enzymes. The efficient in vivo phosphopantetheinylation of E. coli apo-ACP by coexpression with holo-ACP synthase in E. coli BL21(DE3) using fructose as the carbon source is also reported.     

Acylation of plant acyl carrier proteins by acyl-acyl carrier protein synthetase from Escherichia coli

The acyl-acyl carrier protein synthetase from Escherichia coli has been examined for its ability to specifically acylate acyl carrier protein (ACP) from higher plants in order to develop an assay for plant ACP, and to prepare labeled acyl-ACP of plant origin. It was found that the E. coli enzyme was able to acylate ACP from spinach, soybean, avocado, corn, and several other plants. The acylation was very specific because, in crude extracts of spinach leaves where ACP represented approximately 0.1% of the total soluble protein, ACP was shown to be the only protein acylated. In contrast to other E. coli enzymes that display 2- to 10-fold lower rates with plant versus bacterial ACP, the kinetic constants (K_m and V_max) for acyl-ACP synthetase were found to be essentially identical for spinach and E. coli ACP when acylated with palmitic acid. Palmitic, myristic, lauric, stearic, and oleic acid could all be esterified to both spinach and E. coli ACP with similar specificity. Procedures are described that allow the assay of ACP in plant extracts at the nanogram level.     

Acyl carrier protein from Escherichia coli. Structural characterization of short-chain acylated acyl carrier proteins by NMR

Acylated acyl carrier proteins (ACPs) with acyl chain lengths of 2, 4, 6, 8, and 10 carbons were investigated by NMR and nuclear Overhauser methods at 500 MHz. Chemical shift changes of downfield aromatic and upfield, ring-current-shifted, isoleucine proton resonances monotonically vary as a function of acyl chain length with the most prominent shifts occurring with chain lengths between four and six carbons. Chemical shifts are largest for one of the two phenylalanines; however, substantial shifts do exist for Tyr-71, His-75, and two isoleucines. Since these residues are distributed throughout the molecule, their associated resonance chemical shifts are most probably explained by an induced conformational change. Comparative NOE measurements on reduced ACP (ACP-SH) and ACP-S-C8 suggest, however, that these induced conformational changes are small except for around one of the phenylalanines. A tertiary structural model for acyl-ACP consistent with our previous model for ACP-SH [Mayo, K. H., Tyrell, P. M., & Prestegard, J. H. (1983) Biochemistry 22, 4485-4493] is presented.     

Amino acid residues of Escherichia coli acyl carrier protein involved in heterologous protein interactions

Acyl carrier protein (ACP) is a small, highly conserved protein with an essential role in a myriad of reactions throughout lipid metabolism in plants and bacteria where it interacts with a remarkable diversity of proteins. The nature of the proper recognition and precise alignment between the protein moieties of ACP and its many interactive proteins is not understood. Residues conserved among ACPs from numerous plants and bacteria were considered as possibly being crucial to ACP's function, including protein-protein interaction, and a method of identifying amino acid residue clusters of high hydrophobicity on ACP's surface was used to estimate residues possibly involved in specific ACP-protein interactions. On the basis of this information, single-site mutation analysis of multiple residues, one at a time, of ACP was used to probe the identities of potential contact residues of ACPSH or acyl-ACP involved in specific interactions with selected enzymes. The roles of particular ACP residues were more precisely defined by site-directed fluorescence analyses of various myristoyl-mutant-ACPs upon specific interaction with the Escherichia coli hemolysin-activating acyltransferase, HlyC. This was done by selectively labeling each mutated site, one at a time, with an environmentally sensitive fluoroprobe and observing its fluorescence behavior in the absence and presence of HlyC. Consequently, a picture of the portion of ACP involved in selected macromolecular interaction has emerged.     

Amide exchange rates in Escherichia coli acyl carrier protein: correlation with protein structure and dynamics.

The acyl carrier protein (ACP) of Escherichia coli is a 77-amino acid, highly negatively charged three-helix protein that plays a central role in fatty acid biosynthesis. Previous NMR studies have suggested the presence of multiple conformations and marginally stable secondary structural elements. The stability of these elements is now examined by monitoring amide exchange in apo-ACP using NMR-based methods. Because ACP exhibits many rapid exchange rates, application of traditional isotope exchange methods is difficult. In one approach, heteronuclear correlation experiments with pulsed field-gradient coherence selection have reduced the time needed to collect two-dimensional 1H-15N correlation spectra to the point where measurement of exchange of amide protons for deuterium on the timescale of minutes can be made. In another approach, water proton selective inversion-exchange experiments were performed to estimate the exchange rates of protons exchanging on timescales of less than a second. Backbone amide protons in the region of helix II were found to exchange significantly more rapidly than those in helices I and III, consistent with earlier structural models suggesting a dynamic disruption of the second helix. Highly protected amides occur on faces of the helices that may pack into a hydrophobic core present in a partially disrupted state.     

Holo-(acyl carrier protein) synthase and phosphopantetheinyl transfer in Escherichia coli

Holo-(acyl carrier protein) synthase (AcpS) post-translationally modifies apoacyl carrier protein (apoACP) via transfer of 4'-phosphopantetheine from coenzyme A (CoA) to the conserved serine 36 gamma-OH of apoACP. The resulting holo-acyl carrier protein (holo-ACP) is then active as the central coenzyme of fatty acid biosynthesis. The acpS gene has previously been identified and shown to be essential for Escherichia coli growth. Earlier mutagenic studies isolated the E. coli MP4 strain, whose elevated growth requirement for CoA was ascribed to a deficiency in holoACP synthesis. Sequencing of the acpS gene from the E. coli MP4 strain (denoted acpS1) showed that the AcpS1 protein contains a G4D mutation. AcpS1 exhibited a approximately 5-fold reduction in its catalytic efficiency when compared with wild type AcpS, accounting for the E. coli MP4 strain phenotype. It is shown that a conditional acpS mutant accumulates apoACP in vivo under nonpermissive conditions in a manner similar to the E. coli MP4 strain. In addition, it is demonstrated that the gene product, YhhU, of a previously identified E. coli open reading frame can completely suppress the acpS conditional, lethal phenotype upon overexpression of the protein, suggesting that YhhU may be involved in an alternative pathway for phosphopantetheinyl transfer and holoACP synthesis in E. coli.