Identification and characterization of a GDSL esterase gene located proximal to the swr quorum-sensing system of Serratia liquefaciens MG1

Molecular cloning, overexpression, characterization, and In silico modelling analysis of a novel GDSL autotransporter-dependent outer membrane lipase (OML) of Pseudomonas guariconensis

The outer membrane lipase (oml) gene, encoding a novel autotransporter-dependent lipase from Pseudomonas guariconensis, was cloned and sequenced. The oml gene has an open reading frame of 1866 bp. It encodes the 621 amino acid autotransporter-dependent GDSL lipase (OML), which has the highest sequence similarity (64.08 %) with the EstA of Pseudomonas aeruginosa (PDB:3kvn.1. A). OML was expressed and purified, which showed a purified band of approximately 70 kDa. The purified enzyme showed maximum activity at pH 9 and 40 °C. Substrate specificity studies and kinetic study by Lineweaver-Burk plot of purified OML showed Km of 1.27 mM and Vmax of 333.33 U/mL with p-nitrophenyl palmitate. The purified enzyme showed good stability in the presence of hexane, methanol, and ethanol, while the presence of the metal ion Mg2+ showed maximum lipase activity. Bioinformatics analysis supported the in vitro findings by predicting enzyme substrate specificity towards long-chain fatty acids and fatty acids with shorter chain lengths. The stability of the interaction of the protein-ligand complex (OML-ricinoleic acid) was confirmed using MDS and castor oil bioconversion using purified OML was confirmed using High-Performance Liquid Chromatography (HPLC).

DAT, deacylating autotransporter toxin, from Bordetella parapertussis demyristoylates Gαi GTPases and contributes to cough

The pathogenic bacteria Bordetella pertussis and Bordetella parapertussis cause pertussis (whooping cough) and pertussis-like disease, respectively, both of which are characterized by paroxysmal coughing. We previously reported that pertussis toxin (PTx), which inactivates heterotrimeric GTPases of the Gi family through ADP-ribosylation of their α subunits, causes coughing in combination with Vag8 and lipid A in B. pertussis infection. In contrast, the mechanism of cough induced by B. parapertussis, which produces Vag8 and lipopolysaccharide (LPS) containing lipid A, but not PTx, remained to be elucidated. Here, we show that a toxin we named deacylating autotransporter toxin (DAT) of B. parapertussis inactivates heterotrimeric Gi GTPases through demyristoylation of their α subunits and contributes to cough production along with Vag8 and LPS. These results indicate that DAT plays a role in B. parapertussis infection in place of PTx.

Purification and refolding protocol for cold-active recombinant esterase AaSGNH1 from Aphanizomenon flos-aquae expressed as insoluble inclusion bodies

Microbial esterases are a highly desirable tool for numerous biosynthetic and biotechnological applications requiring ester bond cleavage. Once identified, microbial esterases are often produced recombinantly in Escherichia coli to enhance yield and ease of purification. In this study a polyhistidine-tagged SGNH esterase gene (AaSGNH1), originating from the cyanobacterium Aphanizomenon flos-aquae, was cloned into an over-expression plasmid and expressed in BL21(DE3) cells. The recombinant esterase enzyme was produced as inactive inclusion bodies which were insoluble in 8 M urea but readily solubilized by the detergent Empigen BB^®. Crucially, the procurement of active enzyme required controlled removal of detergent during column chromatography and dialysis steps. The refolded esterase was characterized with respect to its ability to catalyze the cleavage of p-nitrophenol esters of different chain lengths (C2, C8, C16). In addition, the temperature and pH optima were determined and it was found that the enzyme was most active at low temperatures (5-15 °C) and under alkaline conditions (pH 8-10). It was found that the kinetic properties of AaSGNH1 were remarkably similar to other SGNH esterases described thereby validating that the protein was effectively refolded. Overall, this study provides a simple strategy for isolating cold-active recombinant esterase enzyme when expressed as inclusion bodies.

Type V Secretion Systems: An Overview of Passenger Domain Functions

Bacteria secrete proteins for different purposes such as communication, virulence functions, adhesion to surfaces, nutrient acquisition, or growth inhibition of competing bacteria. For secretion of proteins, Gram-negative bacteria have evolved different secretion systems, classified as secretion systems I through IX to date. While some of these systems consist of multiple proteins building a complex spanning the cell envelope, the type V secretion system, the subject of this review, is rather minimal. Proteins of the Type V secretion system are often called autotransporters (ATs). In the simplest case, a type V secretion system consists of only one polypeptide chain with a β-barrel translocator domain in the membrane, and an extracellular passenger or effector region. Depending on the exact domain architecture of the protein, type V secretion systems can be further separated into sub-groups termed type Va through e, and possibly another recently identified subtype termed Vf. While this classification works well when it comes to the architecture of the proteins, this is not the case for the function(s) of the secreted passenger. In this review, we will give an overview of the functions of the passengers of the different AT classes, shedding more light on the variety of functions carried out by type V secretion systems.

Rv1075c of Mycobacterium tuberculosis is a GDSL-Like Esterase and Is Important for Intracellular Survival

Mycobacterium tuberculosis lipid metabolism pathways facilitate access to carbon and energy sources during infection. M. tuberculosis gene Rv1075c was annotated as a conserved hypothetical protein. We identified that Rv1075c amino acid sequence shares similarities with other bacterial lipase/esterases and we demonstrated that it has esterase activity, with preference for short-chain fatty acids, particularly acetate, with highest activity at 45°C, pH 9. Site-direct mutagenesis revealed its activity triad as Ser80, Asp244, and His247. We further determined that rRv1075c hydrolyzed triacetin and tributyrin, and it was mainly distributed in cell wall and membrane. Its expression was induced at pH 4.5, mimicking the acidic phagosome of macrophages. Mutation of Rv1075c led to reduced bacterial growth in THP-1 cells and human peripheral blood mononuclear cell-derived macrophages, and attenuated M. tuberculosis infection in mice. Our data suggest that Rv1075c is involved in ester and fatty acid metabolism inside host cells.

Single-Stranded DNA-Binding Protein and Exogenous RecBCD Inhibitors Enhance Phage-Derived Homologous Recombination in Pseudomonas

The limited efficiency of the available tools for genetic manipulation of Pseudomonas limits fundamental research and utilization of this genus. We explored the properties of a lambda Red-like operon (BAS) from Pseudomonas aeruginosa phage Ab31 and a Rac bacteriophage RecET-like operon (RecTE_Psy) from Pseudomonas syringae pv. syringae B728a. Compared with RecTE_Psy, the BAS operon was functional at a higher temperature indicating potential to be a generic system for Pseudomonas. Owing to the lack of RecBCD inhibitor in the BAS operon, we added Redγ or Pluγ and found increased recombineering efficiencies in P. aeruginosa and Pseudomonas fluorescens but not in Pseudomonas putida and P. syringae. Overexpression of single-stranded DNA-binding protein enhanced recombineering in several contexts including RecET recombination in E. coli. The utility of these systems was demonstrated by engineering P. aeruginosa genomes to create an attenuated rhamnolipid producer. Our work enhances the potential for functional genomics in Pseudomonas.

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The BAS operon is a generic recombineering system for Pseudomonas species

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Single-stranded DNA-binding proteins (SSBs) can stimulate homologous recombination

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The heterologous gam genes can inhibit RecBCD function in Pseudomonas

l-Ascorbyl 2,6-dipalmitate inhibits biofilm formation and virulence in methicillin-resistant Staphylococcus aureus and prevents triacylglyceride accumulation in Caenorhabditis elegans

In the present study, the antibiofilm, antipathogenic and anticarotenogenic potential ofl-ascorbyl 2,6-dipalmitate (ADP) against methicillin-resistantStaphylococcus aureus(MRSA) has been evaluated.

Characterization and expression of a GDSL-like lipase gene from Brassica napus in Nicotiana benthamiana

The GDSL esterase and lipase families play important roles in abiotic stress, pathogen defense, seed development and lipid metabolism. Identifying the lipase activity of the putative GDSL lipase is the prerequisite for dissecting its function. According to the sequence similarity and the conserved domains, we cloned the Brassica napus BnGLIP gene, which encodes a GDSL-like protein. We failed to identify the BnGLIP lipase activity in the bacterium and yeast expression systems. In this paper, we expressed the BnGLIP gene by fusing a 6× His tag in Nicotiana benthamiana and purified the recombinant protein. The extraction buffer contained 1 % (v/v) n-caprylic acid and was able to remove most of the protein impurities. About 50 μg of recombinant BnGLIP was obtained from 1 g of N. benthamiana leaves. The lipase activity was tested with the purified BnGLIP and the maximum enzyme activity reached 17.7 mM/mg. In conclusion, this study found that the recombinant protein BnGLIP expressed in tobacco system was effectively purified and was detected as a GDSL lipase.

QsdH, a novel AHL lactonase in the RND-type inner membrane of marine Pseudoalteromonas byunsanensis strain 1A01261

N-acyl-homoserine lactones (AHLs) are the main quorum-sensing (QS) signals in gram-negative bacteria. AHLs trigger the expression of genes for particular biological functions when their density reaches a threshold. In this study, we identified and cloned the qsdH gene by screening a genomic library of Pseudoalteromonas byunsanensis strain 1A01261, which has AHL-degrading activity. The qsdH gene encoded a GDSL hydrolase found to be located in the N-terminus of a multidrug efflux transporter protein of the resistance-nodulation-cell division (RND) family. We further confirmed that the GDSL hydrolase, QsdH, exhibited similar AHL-degrading activity to the full-length ORF protein. QsdH was expressed and purified to process the N-terminal signal peptide yielding a 27-kDa mature protein. QsdH was capable of inactivating AHLs with an acyl chain ranging from C₄ to C₁₄ with or without 3-oxo substitution. High-performance liquid chromatography (HPLC) and electrospray ionization-mass spectrometry (ESI-MS) analyses showed that QsdH functioned as an AHL lactonase to hydrolyze the ester bond of the homoserine lactone ring of AHLs. In addition, site-directed mutagenesis demonstrated that QsdH contained oxyanion holes (Ser-Gly-Asn) in conserved blocks (I, II, and III), which had important roles in its AHL-degrading activity. Furthermore, the lactonase activity of QsdH was slightly promoted by several divalent ions. Using in silico prediction, we concluded that QsdH was located at the first periplasmic loop of the multidrug efflux transporter protein, which is essential to substrate selectivity for these efflux pumps. These findings led us to assume that the QsdH lactonase and C-terminal efflux pump might be effective in quenching QS of the P. byunsanensis strain 1A01261. Moreover, it was observed that recombinant Escherichia coli producing QsdH proteins attenuated the plant pathogenicity of Erwinia carotovora, which might have potential to control of gram-negative pathogenic bacteria.

Characterization and immobilization of a novel SGNH hydrolase (Est24) from Sinorhizobium meliloti

A novel oligomeric SGNH hydrolase (Est24) from Sinorhizobium meliloti was identified, actively expressed in Escherichia coli, characterized, and immobilized for industrial application. Sequence analysis of Est24 revealed a putative catalytic triad (Ser¹³-Asp¹⁶³-His¹⁶⁹), with moderate homology to other SGNH hydrolases. Est24 was more active toward short-chain esters, such as p-nitrophenyl acetate, butyrate, and valerate, while the S13A mutant completely lost its activity. Moreover, the activity of Est24 toward α- and β-naphthyl acetate, and enantioselectivity on (R)- and (S)-methyl-3-hydroxy-2-methylpropionate were tested. Est24 exhibited optimum activity at mesophilic temperature ranges (45-55 °C), and slightly alkaline pH (8.0). Structural and mutagenesis studies revealed critical residues involved in the formation of a catalytic triad and substrate-binding pocket. Cross-linked enzyme aggregates (CLEAs) of Est24 with and without amyloid fibrils were prepared, and amyloid fibril-linked Est24 with amyloid fibrils retained 83 % of its initial activity after 1 h of incubation at 60 °C. The high thermal stability of immobilized Est24 highlights its potential in the pharmaceutical and chemical industries.

Characterization, amyloid formation, and immobilization of a novel SGNH hydrolase from Listeria innocua 11262

A novel oligomeric hydrolase (LI22) from Listeria innocua CLIP 11262 was identified, characterized, and immobilized for industrial application. Sequence analysis of LI22 revealed a putative catalytic triad (Ser(10)-Asp(176)-His(179)), and a conserved sequence motif Ser(S)(10)-Gly(G)(77)-Asn(N)(79)-His(H)(179) with moderate identities (<30%) with other members of the SGNH-hydrolase superfamily. LI22 was able to hydrolyze p-nitrophenyl acetate, α- and β-naphthyl acetate, while the S10A mutant completely lost its activity. Structural properties of LI22 were investigated using gel filtration, circular dichroism (CD), fluorescence, molecular modeling, and gel filtration. We have shown that upon incubation in 30% TFE or 50% ethanol solution, LI22 was transformed into curly amyloid fibrils. Cross-linked enzyme aggregates of LI22 were prepared by precipitating the enzyme with ammonium sulfate and subsequent cross-linking with glutaraldehyde. Higher thermal and chemical stability, as well as good durability after repeated use of the LI22-CLEA, highlight its potential applicability as a biocatalyst in the pharmaceutical and chemical industries.

Gene cloning and characterization of a novel thermophilic esterase from Fervidobacterium nodosum Rt17-B1

A bioinformatic screening of the genome of the thermophilic bacterium Fervidobacterium nodosum Rt17-B1 for esterhydrolyzing enzymes revealed a putative bacterial esterase (FNE) encoded by Fond_1301 with typical GDSL family motifs. To confirm its putative esterase function, the FNE gene was cloned, functionally expressed in Escherichia coli, and purified to homogeneity. Recombinant FNE exhibited the highest esterase activity of 14,000 U/mg with p-nitrophenyl acetate (pNPC(2)) as substrate. The catalytic efficiency (k(cat)/K(m)) toward p-nitrophenyl acetate (C(2)) was approximately 120-fold higher than toward p-nitrophenyl butyrate (C(4)). No significant esterase activity was observed for the substrates with a chain length > or =C(8). The monomeric enzyme has a molecular mass of 27.5 kDa and exhibits optimal activity around 75 degrees C, at pH 8.5. Its thermostability is relatively high with a half-life of 80 min at 70 degrees C, but less stable compared with some other hyperthermophilic esterases. A structural model was constructed using acetylesterase from Aspergillus aculeatus as a template. The structure showed an alpha/beta-hydrolase fold and indicated the presence of a typical catalytic triad consisting of a serine, aspartate, and histidine, which was verified by site-directed mutagenesis. Sequence analysis showed that FNE was only distantly related to other esterases. A comparison of the conserved motifs shared with GDSL proteins revealed that FNE could be grouped into GDSL family and was further classified as SGNH hydrolase.

Examination of Xenorhabdus nematophila lipases in pathogenic and mutualistic host interactions reveals a role for xlpA in nematode progeny production

Xenorhabdus nematophila is a gammaproteobacterium and broad-host-range insect pathogen. It is also a symbiont of Steinernema carpocapsae, the nematode vector that transports the bacterium between insect hosts. X. nematophila produces several secreted enzymes, including hemolysins, lipases, and proteases, which are thought to contribute to virulence or nutrient acquisition for the bacterium and its nematode host in vivo. X. nematophila has two lipase activities with distinct in vitro specificities for Tween and lecithin. The gene encoding the Tween-specific lipase, xlpA, has been identified and is not required for X. nematophila virulence in one insect host, the tobacco hornworm Manduca sexta. However, the gene encoding the lecithin-specific lipase activity is not currently known. Here, we identify X. nematophila estA, a gene encoding a putative lecithinase, and show that an estA mutant lacks in vitro lipase activity against lecithin but has wild-type virulence in Manduca sexta. X. nematophila secondary-form phenotypic variants have higher in vitro lecithinase activity and estA transcript levels than do primary-form variants, and estA transcription is negatively regulated by NilR, a repressor of nematode colonization factors. We establish a role for xlpA, but not estA, in supporting production of nematode progeny during growth in Galleria mellonella insects. Future research is aimed at characterizing the biological roles of estA and xlpA in other insect hosts.

Isolation and characterization of Xenorhabdus nematophila transposon insertion mutants defective in lipase activity against Tween

We identified Xenorhabdus nematophila transposon mutants with defects in lipase activity. One of the mutations, in yigL, a conserved gene of unknown function, resulted in attenuated virulence against Manduca sexta insects. We discuss possible connections between lipase production, YigL, and specific metabolic pathways.

Enterobacterial common antigen integrity is a checkpoint for flagellar biogenesis in Serratia marcescens

Serratia marcescens strains are ubiquitous bacteria isolated from environmental niches, such as soil, water, and air, and also constitute emergent nosocomial opportunistic pathogens. Among the numerous extracellular factors that S. marcescens is able to produce, the PhlA phospholipase is the only described exoprotein secreted by the flagellar apparatus while simultaneously being a member of the flagellar regulon. To gain insight into the regulatory mechanism that couples PhlA and flagellar expression, we conducted a generalized insertional mutagenesis and screened for PhlA-deficient strains. We found that three independent mutations in the wec cluster, which impaired the assembly of enterobacterial common antigen (ECA), provoked the inhibition of PhlA expression. Swimming and swarming assays showed that in these strains, motility was severely affected. Microscopic examination and flagellin immunodetection demonstrated that a strong defect in flagellum expression was responsible for the reduced motility in the wec mutant strains. Furthermore, we determined that in the ECA-defective strains, the transcriptional cascade that controls flagellar assembly was turned off due to the down-regulation of flhDC expression. These findings provide a new perspective on the physiological role of the ECA, providing evidence that in S. marcescens, its biosynthesis conditions the expression of the flagellar regulon.

The autotransporter esterase EstA of Pseudomonas aeruginosa is required for rhamnolipid production, cell motility, and biofilm formation

Pseudomonas aeruginosa PAO1 produces the biodetergent rhamnolipid and secretes it into the extracellular environment. The role of rhamnolipids in the life cycle and pathogenicity of P. aeruginosa has not been completely understood, but they are known to affect outer membrane composition, cell motility, and biofilm formation. This report is focused on the influence of the outer membrane-bound esterase EstA of P. aeruginosa PAO1 on rhamnolipid production. EstA is an autotransporter protein which exposes its catalytically active esterase domain on the cell surface. Here we report that the overexpression of EstA in the wild-type background of P. aeruginosa PAO1 results in an increased production of rhamnolipids whereas an estA deletion mutant produced only marginal amounts of rhamnolipids. Also the known rhamnolipid-dependent cellular motility and biofilm formation were affected. Although only a dependence of swarming motility on rhamnolipids has been known so far, the other kinds of motility displayed by P. aeruginosa PAO1, swimming and twitching, were also affected by an estA mutation. In order to demonstrate that EstA enzyme activity is responsible for these effects, inactive variant EstA* was constructed by replacement of the active serine by alanine. None of the mutant phenotypes could be complemented by expression of EstA*, demonstrating that the phenotypes affected by the estA mutation depend on the enzymatically active protein.

Quorum sensing in Serratia

Many bacteria use cell-cell communication to monitor their population density, synchronize their behaviour and socially interact. This communication results in a coordinated gene regulation and is generally called quorum sensing. In gram-negative bacteria, the most common quorum signal molecules are acylated homoserine lactones (AHLs), although other low-molecular-mass signalling molecules have been described such as Autoinducer-2 (AI-2). The phenotypes that are regulated in Serratia species by means of AHLs are remarkably diverse and of profound biological and ecological significance, and often interconnected with other global regulators. Furthermore, AHL- and AI-2-mediated systems (less profoundly studied) are continuously being discovered and explored in Serratia spp., many having interesting twists on the basic theme. Therefore, this review will highlight the current known quorum sensing systems in Serratia spp., including the important nosocomial pathogen Serratia marcescens.

Lipolytic enzymes in Myxococcus xanthus

The genome of Myxococcus xanthus encodes lipolytic enzymes in three different families: patatin lipases, alpha/beta hydrolases, and GDSL lipases. One member of each family was characterized. The protein encoded by MXAN_3852 contains motifs characteristic of patatins. MXAN_5522 encodes a protein with the G-X-S-X-G motif characteristic of the lipase subfamily of alpha/beta hydrolases. MXAN_4569 encodes a member of the GDSL family of lipolytic enzymes. Strains with deletions of MXAN_5522 and MXAN_4569 undergo faster development and earlier myxospore formation than the wild-type strain. The MXAN_5522 mutation results in spore yields substantially higher than those seen for wild-type cells. Gene expression analysis using translational lacZ fusions indicates that while all three genes are expressed during development, only MXAN_5522 and MXAN_4569 are expressed during vegetative growth. The proteins encoded by these genes were overexpressed using a T7 RNA polymerase transcription (pET102/D-TOPO) system in Escherichia coli BL21 Star (DE3) cells. The substrate specificities of the purified enzymes were investigated using p-nitrophenyl esters with chain lengths from C(2) to C(16). These enzymes preferentially hydrolyzed esters of short-chain fatty acids, yielding the highest activity with p-nitrophenyl acetate.

Effect of non-enzymatic glycation on esterase activities of hemoglobin and myoglobin

Heme proteins--hemoglobin and myoglobin possess esterase activities. Studies with purified hemoglobin from normal individuals and diabetic patients revealed that the esterase activity as measured from hydrolysis of p-nitrophenyl acetate (p-NPA) was higher in diabetic condition and increased progressively with extent of the disease. HbA(1c), the major glycated hemoglobin, which increases proportionately with blood glucose level in diabetes mellitus, exhibited more esterase activity than the non-glycated hemoglobin fraction, HbA(0), as demonstrated spectrophotometrically as well as by activity staining. Glycation influenced esterase activity of hemoglobin by increasing the affinity for the substrate and the rate of the reaction. Both HbA(0) and HbA(1c)-mediated catalysis of p-NPA hydrolysis was pH-dependent. Esterase activity of in vitro-glycated myoglobin (GMb) was also higher than that of its non-glycated analog (Mb). The amplified esterase activities of hemoglobin and myoglobin might be associated with glycation-induced structural modifications of the proteins.

A novel lipolytic enzyme, YcsK (LipC), located in the spore coat of Bacillus subtilis, is involved in spore germination

The predicted amino acid sequence of Bacillus subtilis ycsK exhibits similarity to the GDSL family of lipolytic enzymes. Northern blot analysis showed that ycsK mRNA was first detected from 4 h after the onset of sporulation and that transcription of ycsK was dependent on SigK and GerE. The fluorescence of the YcsK-green fluorescent protein fusion protein produced in sporulating cells was detectable in the mother cell but not in the forespore compartment under fluorescence microscopy, and the fusion protein was localized around the developing spores dependent on CotE, SafA, and SpoVID. Inactivation of the ycsK gene by insertion of an erythromycin resistance gene did not affect vegetative growth or spore resistance to heat, lysozyme, or chloroform. The germination of ycsK spores in a mixture of L-asparagine, D-glucose, D-fructose, and potassium chloride and LB medium was also the same as that of wild-type spores, but the mutant spores were defective in L-alanine-stimulated germination. In addition, zymogram analysis demonstrated that the YcsK protein heterologously expressed in Escherichia coli showed lipolytic activity. We therefore propose that ycsK should be renamed lipC. This is the first study of a bacterial spore germination-related lipase.

Isolation and Expression Analysis of a GDSL-like Lipase Gene from Brassica napus L

As lipolytic enzymes, GDSL lipases play an important role in plant growth and development. In order to identify their functions and roles, the full-length cDNA of a GDSL lipase gene, designated BnLIP2, was isolated from Brassica napus L. BnLIP2 was 1,300 bp long, with 1,122 bp open reading frame (ORF) encoding 373 amino acid residues. Sequence analysis indicated that BnLIP2 belonged to GDSL family. Southern blot analysis indicated that BnLIP2 belonged to a small gene family in rapeseed genome. RT-PCR analysis revealed that BnLIP2 was a tissue-specific expressing gene during reproductive growth and strongly expressed during seed germination. BnLIP2 expression could not be detected until three days after germination, and it subsequently became stronger. The transcript of this gene was deficient in root of seedlings growing at different stages. When juvenile seedlings were treated by methyl jasmonate (MeJ), salicylic acid (SA) and naphthalene acetic acid (NAA), BnLIP2 expression could not be induced in root. Our study implicates that BnLIP2 probably plays an important role in rapeseed germination, morphogenesis, flowering, but independent of root growth and development.

Recent advances in techniques of liver resection

The role of liver resection for benign and malignant hepatobiliary diseases is expanding because of the markedly reduced operative mortality in recent years, as the result of better patient selection, improved surgical techniques, and better perioperative management. The major technical challenge of liver resection is control of bleeding during transection of liver parenchyma. Ultrasonic dissector and clamp crushing are the two techniques used most frequently in liver transection. In recent years, new instruments have been developed for liver transection with an aim to reduce bleeding. Other important advances in liver surgery that have contributed to improved perioperative outcomes include intraoperative ultrasound (IOUS), use of vascular staplers, and reduced bleeding by the development of low central venous pressure anesthesia. Laparoscopy is useful for staging purposes, and laparoscopic liver resection is gaining popularity due to the availability of new laparoscopic instruments for liver transection. Development of local ablative therapies for liver tumors, such as radiofrequency (RF) ablation, is posing a competition to liver resection. However, such techniques also have allowed expansion of indication for hepatic resection to patients with bilobar tumors, and thermal ablative technologies have been used for liver transection. This chapter reviews the current techniques of liver resection.

GDSL family of serine esterases/lipases

GDSL esterases and lipases are hydrolytic enzymes with multifunctional properties such as broad substrate specificity and regiospecificity. They have potential for use in the hydrolysis and synthesis of important ester compounds of pharmaceutical, food, biochemical, and biological interests. This new subclass of lipolytic enzymes possesses a distinct GDSL sequence motif different from the GxSxG motif found in many lipases. Unlike the common lipases, GDSL enzymes do not have the so called nucleophile elbow. Studies show that GDSL hydrolases have a flexible active site that appears to change conformation with the presence and binding of the different substrates, much like the induced fit mechanism proposed by Koshland. Some of the GDSL enzymes have thioesterase, protease, arylesterase, and lysophospholipase activity, yet they appear to be the same protein with similar molecular weight ( approximately 22-60 kDa for most esterases), although some have multiple glycosylation sites with higher apparent molecular weight. GDSL enzymes have five consensus sequence (I-V) and four invariant important catalytic residues Ser, Gly, Asn, and His in blocks I, II, III, and V, respectively. The oxyanion structure led to a new designation of these enzymes as SGNH-hydrolase superfamily or subfamily. Phylogenetic analysis revealed that block IIA which belonged to the SGNH-hydrolases was found only in clade I. Therefore, this family of hydrolases represents a new example of convergent evolution of lipolytic enzymes. These enzymes have little sequence homology to true lipases. Another important differentiating feature of GDSL subfamily of lipolytic enzymes is that the serine-containing motif is closer to the N-terminus unlike other lipases where the GxSxG motif is near the center. Since the first classification of these subclass or subfamily of lipases as GDSL(S) hydrolase, progress has been made in determining the consensus sequence, crystal structure, active site and oxyanion residues, secondary structure, mechanism of catalysis, and understanding the conformational changes. Nevertheless, much still needs to be done to gain better understanding of in vivo biological function, 3-D structure, how this group of enzymes evolved to utilize many different substrates, and the mechanism of reactions. Protein engineering is needed to improve the substrate specificity, enantioselectivity, specific activity, thermostability, and heterologous expression in other hosts (especially food grade microorganisms) leading to eventual large scale production and applications. We hope that this review will rekindle interest among researchers and the industry to study and find uses for these unique enzymes.

AraPerox. A database of putative Arabidopsis proteins from plant peroxisomes

To identify unknown proteins from plant peroxisomes, the Arabidopsis genome was screened for proteins with putative major or minor peroxisome targeting signals type 1 or 2 (PTS1 or PTS2), as defined previously (Reumann S [2004] Plant Physiol 135: 783-800). About 220 and 60 proteins were identified that carry a putative PTS1 or PTS2, respectively. To further support postulated targeting to peroxisomes, several prediction programs were applied and the putative targeting domains analyzed for properties conserved in peroxisomal proteins and for PTS conservation in homologous plant expressed sequence tags. The majority of proteins with a major PTS and medium to high overall probability of peroxisomal targeting represent novel nonhypothetical proteins and include several enzymes involved in beta-oxidation of unsaturated fatty acids and branched amino acids, and 2-hydroxy acid oxidases with a predicted function in fatty acid alpha-oxidation, as well as NADP-dependent dehydrogenases and reductases. In addition, large protein families with many putative peroxisomal isoforms were recognized, including acyl-activating enzymes, GDSL lipases, and small thioesterases. Several proteins are homologous to prokaryotic enzymes of a novel aerobic hybrid degradation pathway for aromatic compounds and proposed to be involved in peroxisomal biosynthesis of plant hormones like jasmonic acid, auxin, and salicylic acid. Putative regulatory proteins of plant peroxisomes include protein kinases, small heat shock proteins, and proteases. The information on subcellular targeting prediction, homology, and in silico expression analysis for these Arabidopsis proteins has been compiled in the public database AraPerox to accelerate discovery and experimental investigation of novel metabolic and regulatory pathways of plant peroxisomes.

Quorum sensing and swarming migration in bacteria

Bacterial cells can produce and sense signal molecules, allowing the whole population to initiate a concerted action once a critical concentration (corresponding to a particular population density) of the signal has been reached, a phenomenon known as quorum sensing. One of the possible quorum sensing-regulated phenotypes is swarming, a flagella-driven movement of differentiated swarmer cells (hyperflagellated, elongated, multinucleated) by which bacteria can spread as a biofilm over a surface. The glycolipid or lipopeptide biosurfactants thereby produced function as wetting agent by reducing the surface tension. Quorum sensing systems are almost always integrated into other regulatory circuits. This effectively expands the range of environmental signals that influence target gene expression beyond population density. In this review, we first discuss the regulation of AHL-mediated surface migration and the involvement of other low-molecular-mass signal molecules (such as the furanosyl borate diester AI-2) in biosurfactant production of different bacteria. In addition, population density-dependent regulation of swarmer cell differentiation is reviewed. Also, several examples of interspecies signalling are reported. Different signal molecules either produced by bacteria (such as other AHLs and diketopiperazines) or excreted by plants (such as furanones, plant signal mimics) might influence the quorum sensing-regulated swarming behaviour in bacteria different from the producer. On the other hand, specific bacteria can reduce the local available concentration of signal molecules produced by others. In the last part, the role and regulation of a surface-associated movement in biofilm formation is discussed. Here we also describe how quorum sensing may disperse existing biofilms and control the interaction between bacteria and higher organisms (such as the Rhizobium-bean symbiosis).