Molecular cloning and nucleotide sequence of rat lingual lipase cDNA

Relevant pH and lipase for in vitro models of gastric digestion

The development of in vitro digestion models relies on the availability of in vivo data such as digestive enzyme levels and pH values recorded in the course of meal digestion. The variations of these parameters along the GI tract are important for designing dynamic digestion models but also static models for which the choice of representative conditions of the gastric and intestinal conditions is critical. Simulating gastric digestion with a static model and a single set of parameters is particularly challenging because the variations in pH and enzyme concentration occurring in the stomach are much broader than those occurring in the small intestine. A review of the literature on this topic reveals that most models of gastric digestion use very low pH values that are not representative of the fed conditions. This is illustrated here by showing the variations in gastric pH as a function of meal gastric emptying instead of time. This representation highlights those pH values that are the most relevant for testing meal digestion in the stomach. Gastric lipolysis is still largely ignored or is performed with microbial lipases. In vivo data on gastric lipase and lipolysis have however been collected in humans and dogs during test meals. The biochemical characterization of gastric lipase has shown that this enzyme is rather unique among lipases: (i) stability and activity in the pH range 2 to 7 with an optimum at pH 4-5.4; (ii) high tensioactivity that allows resistance to bile salts and penetration into phospholipid layers covering TAG droplets; (iii) sn-3 stereospecificity for TAG hydrolysis; and (iv) resistance to pepsin. Most of these properties have been known for more than two decades and should provide a rational basis for the replacement of gastric lipase by other lipases when gastric lipase is not available.

Understanding the lipid-digestion processes in the GI tract before designing lipid-based drug-delivery systems

Many of the compounds present in lipid-based drug-delivery systems are esters, such as acylglycerols, phospholipids, polyethyleneglycol mono- and di-esters and polysorbate, which can be hydrolyzed by the various lipolytic enzymes present in the GI tract. Lipolysis of these compounds, along with dietary fats, affects the solubility, dispersion and bioavailibity of poorly water-soluble drugs. Pharmaceutical scientists have been taking a new interest in fat digestion in this context, and several studies presenting in vitro gastrointestinal lipolysis models have been published. In most models, it is generally assumed that pancreatic lipase is the main enzyme involved in the gastrointestinal lipolysis of lipid formulations. It was established, however, that gastric lipase, pancreatic carboxyl ester hydrolaze and pancreatic lipase-related protein 2 are the major players involved in the lipolysis of lipid excipients containing acylglycerols and polyethyleneglycol esters. These findings have shown that the lipolysis of lipid excipients may actually start in the stomach and involve several lipolytic enzymes. These findings should therefore be taken into account when testing in vitro the dispersion and bioavailability of poorly water-soluble drugs formulated with lipids. In this review, we present the latest data available about the lipolytic enzymes involved in gastrointestinal lipolysis and suggest tracks for designing physiologically relevant in vitro digestion models.

Molecular characterization, expression profile and association analysis with carcass traits of porcine LCAT gene

The lecithin cholesterol acyltransferase gene (LCAT) plays an important role in lipoprotein metabolism, especially in the process termed 'reverse cholesterol transport'. In this study, we obtained the 1,434 bp mRNA sequence of porcine LCAT including the full coding region and encoding a protein of 472 amino acids. The sequence was deposited into the GenBank under the accession no. EU717835. The genomic sequence of this gene which contains six exons and five introns, is 3,712 bp in length (GQ379050). Bioinformatic analysis of the 5' regulatory region has revealed that some transcription factor Sp1, AP-1, AP-2 and NF-kappaB were represented in this region. Tissue expression analysis showed that the porcine LCAT gene is ubiquitously expressed in all examined tissues. Phylogenetic tree was constructed by aligning the amino acid sequences of different species. Moreover, we found a single nucleotide polymorphism (SNP, C/G266) in intron 1 of the LCAT gene and association analysis showed that it was significantly associated with ratio of lean to fat (P < 0.05), caul fat weight (P < 0.01), leaf fat weight (P < 0.05), carcass length (P < 0.05) and bone percentage (P < 0.05). Our study will lay the groundwork for the further investigations on the detailed physiological function of LCAT in pig models.

Purification, cloning and regulation of a novel acid-lipase-like protein of hamster expressed in lacrimal glands and tears during lactation

We report a novel 48-kDa tear acid-lipase-like protein (TALLP), which is markedly induced in lacrimal glands (LG) and secreted in tears of hamster dams during lactation. TALLP is undetectable in LG and tears of normal hamsters, but is also induced after gonadectomy in both sexes and this is prevented by androgen, estrogen or thyroid hormone treatment. These observations and the obliteration of TALLP upon cessation of lactation suggest that endogenous estrogens (in females) and androgens (in males) completely repress TALLP expression. Purified TALLP is monomeric, contains approximately 18% N-glycosylation and several pI isoforms. TALLP expression was tissue-specific and immunolocalized in LG acinar cells. The cDNA deduced amino-acid sequence of TALLP precursor (398 residue, containing a 19 residues signal-peptide) showed only 43-48% identity with all known mammalian acid-lipases, including even those of other rodents, suggesting that TALLP is a prototype of a new category, within the acid-lipase family. Surprisingly, although the catalytic triad residues and other sequence features important for lipolytic activity are conserved in TALLP, it has no detectable lipase activity. However, TALLP binds the polarity sensitive hydrophobic probe, 1-aminoanthracene (K(d)=12 microM). TALLP might have a unique substrate-specificity or a lipid-binding/carrier function in tears of hamster dams. This is the first report of an acid-lipase-like protein secreted in tears of any species. Since TALLP lacks the usual lipase activity, it can be an excellent model to understand better what other structural features in acid-lipases influence their catalytic activity.

Metabolities of dietary triacylglycerol and diacylglycerol during the digestion process in rats

The present study investigated the metabolic fate of dietary TAG and DAG and also their digestion products in the stomach and small intestine. A diet containing 10% TAG or DAG oil, enriched in 1,3-DAG, was fed to Wistar rats ad libitum for 9 d. After 18 h of fasting, each diet was re-fed ad libitum for 1 h. The weights of the contents of the stomach and small intestine were measured, and the acylglycerol and FFA levels were analyzed by GC at 0, 1, and 4 h after the 1-h re-feeding. The amounts of re-fed diet ingested and the gastric and small intestinal content were not different between the two diet groups. In the TAG diet group, the main products were TAG and DAG, especially 1(3),2-DAG. In addition, 1,3-DAG and 1(3)-MAG were present in the stomach, and the 1,3-DAG levels increased over time after the re-feeding period. In the DAG diet group, the main products in the stomach were DAG, MAG, FFA, and TAG. There were significantly greater amounts of 1,3-DAG, 1(3)-MAG, and FFA in the DAG diet group in the stomach compared with the TAG diet group. The amount of FFA in the stomach relative to the amount of ingested TAG plus DAG in the DAG diet group was higher than that in the TAG diet group. Acylglycerol and FFA levels were considerably lower in the small intestine than in the stomach. These results indicate that, in the stomach, where acyl migration might occur, the digestion products were already different between TAG and DAG oil ingestion, and that DAG might be more readily digested by lingual lipase compared with TAG. Furthermore, almost all of the dietary lipid was absorbed, irrespective of the structure of the acylglycerol present in the small intestine.

Development and analytical validation of an enzyme linked immunosorbent assay for the measurement of canine gastric lipase immunoreactivity in serum

The objective of this study was to develop and analytically validate an enzyme linked immunosorbent assay (ELISA) for measurement of canine gastric lipase immunoreactivity (cGLI). A sandwich ELISA was developed using canine gastric lipase (cGL) purified from canine stomachs and polyclonal antibodies directed against cGL, raised in rabbits and purified by affinity chromatography. The assay was validated by determination of sensitivity, working range, linearity, accuracy, precision, reproducibility, and the upper limit of the control range by determining the 97.5th percentile of serum cGLI concentration in 74 healthy canines. Sensitivity and working range in serum were 200 ng/L and 200 to 39 160 ng/L, respectively. Observed to expected ratios for dilutional parallelism for 3 serum samples and 3 dilutions ranged from 86.1% to 244.2% (mean +/- standard deviation [s]; 125.4% +/- 48.2%). Observed to expected ratios for spiking recoveries for 3 serum samples and 6 spiking concentrations ranged from 66.4% to 152.5% (mean +/- s; 104.5% +/- 22.9%). Intra-assay and interassay variabilities for 3 different serum samples were 25.5%, 9.4%, and 13.4% and 26.0%, 17.2%, and 14.4%, respectively. The upper limit of the control range for serum cGLI was 662 ng/L. We concluded that the ELISA for cGLI described here is highly sensitive and shows a wide working range. However, the validation characteristics for this assay are suboptimal and below values of approximately 2.000 ng/L the assay is more semiquantitative in nature. Despite its limitations, whether this assay is useful for the diagnosis of canine gastric disorders remains to be determined.

From interaction of lipidic vehicles with intestinal epithelial cell membranes to the formation and secretion of chylomicrons

Lipophilic drugs are carried by chylomicrons that are secreted by the small intestine and transported in lymph. This review discusses the digestion, uptake, and transport of dietary lipids and the impact that these processes have on the absorption of lipophilic drugs by the gastrointestinal tract. This chapter complements Dr. Chris Potter's chapter on the "pre-absorptive" events of drug processing and solubilization. This chapter reviews the digestion of lipids in the gastric and intestinal lumen and the role of bile salts in the solubilization of lipid digestion products for uptake by the gut. Both the passive and active uptake of lipid digestion products is discussed. How intestinal lipid transporters located at the brush border membrane may play a role in the uptake of lipids by the enterocytes is examined, as is the regulation of the absorption of cholesterol by the human ATP-binding cassette transporter-1 (ABC1). The intracellular trafficking and the resynthesis of complex lipids from lipid digestion products are explored, and the formation and secretion of chylomicrons are described.

An enzymatically active truncated form (-55 N-terminal residues) of rabbit gastric lipase. Correlation between the enzymatic activity and disulfide bond oxydo-reduction state

Rabbit gastric lipase (RGL) was subjected to proteolysis with trypsin and led to cleavage occurring at three defined sites (Lys-4, Arg-55 and Arg-229). The tryptic hydrolysate contained four fragments: Gly-230-Lys-379 (T1), Gly-56-Arg-229 (T2), Ser-5-Arg-55 (T3), as well as a 45 kDa molecular form consisting of peptides T1 and T2 linked by a disulfide bridge. The tryptic hydrolysate of RGL as well as the 55 N-terminal amino acid deleted forms conserved 30% of the initial enzymatic activity in a tributyrin assay. Two out of the three cysteine residues which are present in all the known gastric lipases were found to be involved in a disulfide bridge. Unlike HGL, RGL appears to have a heterogenous pattern of cysteine residues. The 30% enzymatic activity of RGL persisting after trypsin treatment may be attributable to the 45 kDa molecular form (with the Cys-227-Cys-236 or Cys-227-Cys-244 disulfide bridge). Trypsin-treated HGL, which was completely inactivated, showed that a single location of the disulfide bridge existed between cysteine residues 236 and 244. It can be concluded that the existence of one disulfide bridge is necessary to maintain the lipase activity of the 45 kDa form of RGL.

The Drosophila melanogaster lipase homologs: a gene family with tissue and developmental specific expression

We report the molecular cloning of Drosophila genes encoding putative lipase homologs, Dm lip1, lip2 and lip3, the definition of their structure and the expression patterns during development. These Drosophila lipases are related to acid lipases, with a common GHSQG motif, within a more general consensus GXSXG, identified as the active site shared by all the members of lipase superfamily. The lip1 and lip3 genes are transcribed in different tissues and developmental stages, suggesting that they have different functions. The lip1 gene, coding for a protein similar to digestive lipases, is expressed in ovaries and early embryos and, with a different sized transcript, in all the other developmental stages. The lip3 gene, whose translation product is more similar to lysosomal acid lipases, is expressed only during the larval period. The lip2 gene seems non-functional. The Drosophila putative lipases do not show similarity with the Drosophila yolk proteins that are reported to have sequence similarity with lipoprotein lipases, but share a consistent similarity with lepidopteran proteins reported as egg specific or yolk proteins, probably corresponding to lipase homologs. The results reported here are discussed in relation to the evolution and functions of lipases within the between species.

The complete cDNA sequence encoding dog gastric lipase

Oligodeoxyribonucleotide ligation to single-stranded cDNA (SLIC) and polymerase chain reaction (PCR) techniques were used to clone an entire dog gastric lipase (DGL) cDNA. The size of the cDNA is confirmed by Northern blot analysis. The DGL is synthesized as a 379-amino acid mature polypeptide with a molecular mass of 43176 Da which is preceded by a 19-amino acid signal sequence located at the NH2-terminus. Comparison of the signal sequences reveals a high degree of similitude between the DGL, the human gastric lipase (HGL), the rabbit gastric lipase (RGL) and the rat lingual lipase (RLL).

Mouse lysosomal acid lipase: characterization of the gene and analysis of promoter activity

Lysosomal acid lipase (LAL) is required for the hydrolysis of intracellular cholesteryl esters and triglycerides that are delivered to lysosomes by low density lipoprotein (LDL) receptor-mediated endocytosis. To understand that the expression of LAL mRNA and protein is tissue and cell specifically regulated in mice, genomic clones for the mouse lysosomal acid lipase (mLAL) gene were isolated and characterized. The 6.8 kb of the mLAL gene 5'-flanking region was sequenced. Comparisons of mouse and human LAL genes organization revealed identical intron/exon boundaries, except for intron 1 of the mouse gene, and identical exonic length of exons 3-9. The transcription start sites and exon 1 of mLAL were characterized by 5'-RACE-PCR and S1 nuclease mapping. Transfection of 5' flanking deletions of mLAL luciferase reporter gene construct identified positive and negative regulatory elements that varied with cell type. Transfection of three progressively smaller pieces of intron 1 inserted into an SV40 promoter and luciferase reporter gene revealed an enhancer-like activity in intron 1 that is also cell type specific. These studies provide insight into the basis for regulation of this critical enzyme in lipid metabolism.

5' coding region of the follicular epithelium yolk polypeptide 2 cDNA in the moth, Plodia interpunctella, contains an extended coding region

The 5' region of YP2 cDNA, a follicular epithelium yolk protein subunit in the moth, Plodia interpunctella, shows that the polypeptide contains an extended internal coding region. Partial cDNA clones for YP2 were isolated from a pharate adult female ovarian cDNA expression library in Lambda Zap II by screening with antigen selected YP2 antiserum. The 5' sequence of the YP2 transcript was determined by 5' RACE PCR of ovarian mRNA using YP2 sequence-specific nested primers. The combined cDNA and 5' RACE sequencing showed the YP2 transcript to be 1971 bp in length up to the poly(A) tail with a single open reading frame for a predicted polypeptide of 616 amino acids. Northern analysis showed a single YP2 transcript to be present in ovarian RNA that was approximately 2 kb in length. The predicted amino acid sequence for YP2 from P. interpunctella is most closely related to egg specific protein (ESP) from Bombyx mori and the partial YP2 sequence from Galleria mellonella. YP2 from P. interpunctella also is similar to vertebrate lipases and contains a conserved lipid binding region. However, the 5' coding region of YP2 from P. interpunctella contains an in-frame insert of approximately 438 bp that had replaced an approximately 270-bp region as compared with ESP from B. mori and YP2 of G. mellonella. This suggests that the insert occurred by a recombinational event internal to the YP2 structural gene of P. interpunctella.

Sequence analysis of the CEN12 region of Saccharomyces cerevisiae on a 43.7 kb fragment of chromosome XII including an open reading frame homologous to the human cystic fibrosis transmembrane conductance regulator protein CFTR

In the framework of the European Union BIOTECH project for systematically sequencing the Saccharomyces cerevisiae genome, we determined the nucleotide sequence of a 43.7 kb DNA fragment spanning the centromeric region of chromosome XII. A novel approach was the distribution of sublibraries prepared by the DNA coordinator (J. Hoheisel, Heidelberg, FRG), using a new hybridization-based DNA mapping method, in order to facilitate ordered sequencing. The sequence contains 22 open reading frames (ORFs) longer than 299 bp, including the published sequences for ATS/DPS1, SCD25, SOF1, DRS1, MMM1, DNM1 and the centromeric region CEN12. Five putative ORF products show similarity to known proteins: the leucine zipper-containing ABC transporter L1313p to the yeast Ycflp metal resistance protein, to the yeast putative ATP-dependent permease Yhd5p, to the yeast putative proteins Yk83p and Yk84p, to the human cystic fibrosis transmembrane conductance regulator protein (hCFTR) and to the human multidrug resistance-associated protein hMRP1; L1325p to the Drosophila melanogaster Pumilio protein, to the putative yeast regulatory protein Yg13p and to the yeast protein Mpt5p/Htrlp; L1329p to human lipase A and gastric lipase, to rat lingual lipase and to the putative yeast triglyceride lipase Tg11p; L1341p to the putative yeast protein Yhg4p; and the leucine zipper-containing L1361p to the two yeast proteins 00953p and Ym8156.08p and to the Arabidopsis thaliana protein HYP1. Eight ORFs show no homology to known sequences in the database, three small ORFs are internal and complementary to larger ones and L1301 is complementary overlapping the ATS/DPS1 gene. Additionally three equally spaced ARS consensus sequences were found.

Inhibition studies on calf pregastric esterase: the enzyme has no functional thiol group

Pregastric esterase (PGE) (EC 3.1.1.3) was purified to homogeneity from calf pharyngeal tissue. The enzyme had an apparent molecular mass of 50 kDa, as determined by SDS/PAGE. The serine-binding reagent diethyl p-nitrophenyl phosphate was a potent inhibitor of PGE. This is in accordance with the claim that a functional serine residue is necessary for the lipolytic activity of lipases. PGE was not inhibited by the thiol reagents 5,5'-dithiobis(2-nitrobenzoic acid) or 4,4'-dithiopyridine. A partial inhibition with dodecyldithio-5-(2-nitrobenzoic acid) was observed, but the same degree of inhibition was caused by the non-esterified fatty acid C(12:0). PGE shows a great sequence similarity to gastric lipases. Gastric lipases have three cysteine residues, and two of these form a disulphide bridge. Blocking the remaining free cysteine with thiol reagents inactivates the gastric lipases. The fact that PGE is not inhibited by thiol reagents indicates that PGE has no functional free thiol group. The PGE cDNA codes only for two cysteines, and their involvement in the formation of a disulphide bridge was demonstrated.

Chicken lecithin-cholesterol acyltransferase. Molecular characterization reveals unusual structure and expression pattern

Rapidly growing oocytes in the laying hen are, in addition to the liver, targets of the so-called "reverse cholesterol transport" (RCT) (Vieira, P.M., Vieira, A.V., Sanders, E.J., Steyrer, E., Nimpf, J., and Schneider, W.J. (1995) J. Lipid Res. 36, 601-610), pointing to the importance of this process in nonplacental reproduction. We have begun to delineate the details of this unique transport pathway branch by molecular characterization of the first nonmammalian lecithin-cholesterol acyltransferase (LCAT), the enzyme that catalyzes an early step in RCT. The biological significance of the enzyme is underscored by the high degree of protein sequence identity (73%) maintained from chicken to man. Interestingly, the conservation extends much less to the cysteine residues; in fact, two of the cysteines thought to be important in mammalian enzymes (residues 31 and 184 in man) are absent from the chicken enzyme, providing proof of their dispensability for enzymatic activity. Antibodies prepared against a chicken LCAT fusion protein cross-react with human LCAT and identify a 64-kDa protein present in enzymatically active fractions obtained by hydrophobic chromatography of chicken serum. The developmental and tissue distribution pattern of LCAT in females is striking; during embryogenesis and adolescence, LCAT expression is extremely high in liver but undetectable in brain. Upon onset of laying, however, brain LCAT mRNA increases suddenly and is maintained at levels 5 times higher than in liver, in stark contrast to most mammals. In adult roosters, the levels of LCAT transcripts in brain are lower than in liver. Together with the molecular characterization of chicken LCAT, these newly discovered developmental changes and gender differences in its expression establish the avian oocyte/liver system as a powerful model to delineate in vivo regulatory elements of RCT.

Purification and molecular characterization of lamb pregastric lipase

Lamb pregastric lipase (LPGL) was purified from pharyngeal tissues. The purification procedure was based on an aqueous extract containing 0.7% Tween 80 which was chromatographed on DEAE-cellulose anion-exchanger and adsorbed on HA-Ultrogel followed by gel filtration on Ultrogel AcA-54. The final enzymatic preparation, where the overall activity recovery was 3%, showed a single protein band on SDS-PAGE with a molecular mass of 50 kDa. LPGL is a glycoprotein containing approx. 14% (w/w) of carbohydrate. Extensive deglycosylation using peptide N-glycosidase F yielded a protein with an apparent molecular mass of 43 kDa. An uncontrolled proteolysis of LPGL during the purification lead to a 45 kDa form which was previously observed in human lysosomal acid lipase (HLAL) and rabbit gastric lipase (RGL). The labile bond X54-Leu55 was identified. Isoelectric focusing of LPGL reveals a major band corresponding to an isoelectric point of 4.8. The pure enzyme displayed specific activities of 950 U mg-1, 300 U mg-1 and 30 U mg-1 at pH 6.0, using tributyroylglycerol, trioctanoylglycerol and trioleoylglycerol as substrates, respectively. Using Western blot analysis, a cross-immunoreactivity of LPGL was observed with purified anti-human gastric lipase polyclonal antibodies. Determination of the amino-acid sequence of 62 residues revealed a high degree of homology with other known preduodenal lipases.

A novel variant of lysosomal acid lipase (Leu336-->Pro) associated with acid lipase deficiency and cholesterol ester storage disease

Cholesterol ester storage disease (CESD) is associated with premature atherosclerosis, hepatomegaly, elevated LDL cholesterol levels, and in most cases, low HDL cholesterol levels. Previous studies have shown a G-->A mutation at the 3' splice junction of exon 8 (E8SJM) of the gene encoding lysosomal acid lipase (LAL) in two kindreds with CESD. In a Canadian-Norwegian kindred with this disease, we show this mutation in conjunction with an as yet unknown T-->C transition in exon 10 predicting a Leu336-->Pro (L336P) replacement and an A-->C transversion in exon 2 predicting a T-6P replacement in the prepeptide. Identification of the L336P rather than the T-6P replacement as the second defect underlying CESD in our patient is deduced from three lines of evidence. First, the E8SJM allele is located in cis with the mutation predicting the T-6P-encoding allele but in trans with the L336P-encoding allele; second, the L336P but not the T-6P replacement cosegregates with low LAL activity in the family; third, the T-6P replacement was found in 6 of 28 alleles from subjects with normal lysosomal acid lipase activity, suggesting that this variant represents a frequent nonfunctional polymorphism. Since the residual LAL activity is higher and the clinical phenotype based on plasma lipid values and severity of hepatosplenomegaly is milder in this case than in a previously studied case who was homozygous for the E8SJM allele, we conclude that the L336P variant appears to be associated with a phenotypically mild form of CESD.

The cDNA sequence encoding bovine pregastric esterase

The polymerase chain reaction (PCR) was used to amplify specific parts of the gene encoding calf pregastric esterase (PGE). Primers based on conserved regions in human gastric lipase (HGL) and rat lingual lipase (RLL) were used to screen a cDNA library prepared from calf tongue tissue. This resulted in the cloning of the entire coding sequence for PGE, which exists as a mature 378-amino-acid (aa) polypeptide with a molecular mass of 42,960 Da. The PGE, HGL and RLL genes all share a high degree of identity at both the nucleotide and amino-acid sequence levels. Except for the Gly-Xaa-Ser-Xaa-Gly sequence containing the active site Ser, there is little identity with non-preduodenal lipases.

The lipA gene of Serratia marcescens which encodes an extracellular lipase having no N-terminal signal peptide

The lipA gene encoding an extracellular lipase was cloned from the wild-type strain of Serratia marcescens Sr41. Nucleotide sequencing showed a major open reading frame encoding a 64.9-kDa protein of 613 amino acid residues; the deduced amino acid sequence contains a lipase consensus sequence, GXSXG. The lipase had 66 and 56% homologies with the lipases of Pseudomonas fluorescens B52 and P. fluorescens SIK W1, respectively, but did not show any overall homology with lipases from other origins. The Escherichia coli cells carrying the S. marcescens lipA gene did not secrete the lipase into the medium. The S. marcescens lipase had no conventional N-terminal signal sequence but was also not subjected to any processing at both the N-terminal and C-terminal regions. A specific short region similar to the regions of secretory proteins having no N-terminal signal peptide was observed in the amino acid sequence. Expression of the lipA gene in S. marcescens was affected by the carbon source and the addition of Tween 80.

Mutations at the lysosomal acid cholesteryl ester hydrolase gene locus in Wolman disease

The genomic sequences encoding the human lysosomal acid lipase/cholesteryl esterase (sterol esterase; EC 3.1.1.13) have been isolated and sequenced, and the information has been used to identify mutations in both alleles of the gene from a patient with Wolman disease, an autosomal recessive lysosomal lipid storage disorder. The genomic locus consists of 10 exons spread over 36 kb. The 5' flanking region is G+C-rich and has characteristics of a "housekeeping" gene promoter. One of the identified mutations involves the insertion of a T residue after position 634, resulting in the appearance of an in-frame translation stop signal 13 codons downstream. The second mutation is a T-to-C transition at nucleotide 638. This results in a leucine-to-proline substitution at amino acid 179 and is predicted to lead to the disruption of the alpha-helical structure in a highly conserved region of the protein. These mutations are each capable of completely disrupting the catalytic function of the lysosomal acid cholesteryl ester hydrolase; their presence can account for the extreme phenotype of the lysosomal lipid storage disorder manifested in members of this patient's family.

Purification, characterization and molecular cloning of human hepatic lysosomal acid lipase

Lysosomal acid lipase (LAL) is a hydrolase essential for the intracellular degradation of cholesteryl esters and triacylglycerols. This report describes a multi-step procedure for the purification of LAL from human liver. After solubilization with non-ionic detergent, acid hydrolase activity was purified 17000-fold to apparent homogeneity by sequential chromatography on Concanavalin A Sepharose, carboxymethyl-cellulose, phenyl Superose, Mono S cation exchange and Superose 12 gel-filtration columns. This procedure yielded two silver-staining protein bands of 56 kDa and 41 kDa on SDS/PAGE. Size-exclusion chromatography of the 41-kDa protein indicated that the enzyme was catalytically competent as a monomer of approximately 38 kDa. When assayed in the presence of cholesteryl oleate or trioleoylglycerol, purified acid lipase had Vmax values of 4390 nmol fatty acid.min-1.mg protein and 4756 nmol fatty acid.min-1.mg protein-1, and apparent Km values of 0.142 mM and 0.138 mM, respectively. The purified enzyme was most active at low pH (4.5-5.0) and required non-ionic detergent and ethylene glycol for optimal stability. Incubation of the 41-kDa acid lipase with endoglucosaminidase H reduced the molecular mass by 4-6 kDa, demonstrating Asn-linked glycosylation with high-mannose oligosaccharides. Deglycosylation did not affect enzymic activity, indicating that carbohydrates are not required for LAL activity. Based on partial peptide sequence, an oligonucleotide was synthesized and utilized to isolate LAL cDNA clones from a human liver cDNA library. A full-length LAL cDNA contained 2626 nucleotides and coded for a predicted protein of 372 amino acids, preceded by a 27 residue hydrophobic signal peptide. Hepatic LAL differed from fibroblast acid lipase at the N-terminus and revealed extensive similarities with human gastric lipase and rat lingual lipase, confirming a gene family of acid lipases. Northern hybridization using the complete LAL cDNA as a radiolabeled probe indicated striking differences in mRNA expression among human tissues. LAL mRNA was most abundant in brain, lung, kidney and mammary gland. Placenta and HeLa cells expressed intermediate amounts of LAL mRNA, while RNA extracted from liver and heart showed low levels of expression.

Hormone-sensitive lipase is closely related to several bacterial proteins, and distantly related to acetylcholinesterase and lipoprotein lipase: identification of a superfamily of esterases and lipases

We have sequenced a gene from Bacillus acidocaldarius which encodes an open reading frame (ORF3) of 310 amino acids. The ORF3 was found to be related to the mammalian hormone-sensitive lipase (HSL). Searching the protein data base revealed five other bacterial proteins related to the HSL. Upon further sequence comparisons this HSL-group was found to be related to the family of carboxylesterases, and to a family of lipases (lipoprotein, hepatic and pancreatic lipases). The evolutionary relationship of these serine-dependent hydrolytic enzymes has not been studied previously, and it has not been known that these proteins belong to the same superfamily. Finally, the alignment of the HSL with the bacterial proteins allowed us to infer the location of the hormone-sensitive regulatory domain of the HSL-protein.

Positional specificity of gastric hydrolysis of long-chain n-3 polyunsaturated fatty acids of seal milk triglycerides

Long-chain n-3 polyunsaturated fatty acids (n-3 PUFA) of marine oils are important dietary components for both infants and adults, and are incorporated into milks following maternal dietary intake. However, little is known about the hydrolysis of these PUFA from milk triglycerides (TG) by lipases in suckling young. Seals, like humans, possess gastric lipase; however, the milk lipids of seals and sea lions are almost devoid of the readily hydrolyzable medium-chain fatty acids, and are characterized by a large percentage (10-30%) of n-3 PUFA. Gastric hydrolysis of milk lipids was studied in vivo in suckling pups of three species (the California sea lion, the harp seal and the hooded seal) in order to elucidate the actions and specificity of gastric lipases on milk TG in relation to fatty acid composition and TG structure. Regardless of milk fat content (31-61% fat) or extent of gastric hydrolysis (10-56%), the same fatty acids were preferentially released in all three species, as determined by their relative enrichment in the free fatty acid (FFA) fraction. In addition to 16:1 and 18:0, these were the PUFA of 18 carbons and longer, except for 22:6n-3. Levels of 20:5n-3 were most notably enriched in FFA, at up to five times that found in the TG. Although 22:6n-3 was apparently also released from the TG (reduced in the diglyceride), it was also notably reduced in FFA.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural relationship between lipases and peptidases of the prolyl oligopeptidase family

In prolyl oligopeptidase and its homologues, which constitute a new serine protease family, the order of the catalytic Ser and His residues in the amino acid sequence is the reverse of what is found in the trypsin and subtilisin families. The exact position of the third member of the catalytic triad, an Asp residue, has not yet been identified in the new family. Recent determination of the three-dimensional structures of pancreatic and microbial lipases has shown that the order of their catalytic residues is Ser, Asp, His, and this fits the order Ser, His of prolyl oligopeptidase. However, there is no sequence homology between lipases and peptidases, except for a 10-residue segment, which encompasses the essential Ser, and for the immediate vicinity of the catalytic Asp and His residues. This comparison identifies the catalytic Asp residue in the prolyl oligopeptidase family. The relative positions of the three catalytic residues in peptidases and microbial lipases were the same and this indicated structural and possibly evolutionary relationship between the two families.

Purification and characterization of lamb pregastric lipase

Lamb pregastric lipase was purified from a commercial source using delipidation, solubilization with KSCN, acid-precipitation, pepsin-digestion, affinity chromatography with agarose-Cibacron Blue F3GA, gel filtration, and elution from a native 10% (w/v) polyacrylamide gel. The enzyme had a single subunit of 68,000 Da with maximum esterase activity when measured at pH 6.0 and 30 degrees C. The enzyme preferentially hydrolyzed short- and medium-chain (C4, C6, and C8) synthetic esters and short-chain (C4 and C6) monoacid triglycerides. The NH2-terminal sequence demonstrated high homology with gastric and lingual lipases.

Kinetics and mechanisms of reactions catalysed by immobilized lipases

This review focuses on the kinetics and mechanisms of reactions catalysed by immobilized lipases. The effects of pH, temperature, and various substances on the catalytic properties of immobilized lipases and on the processes by which they are deactivated are reviewed and discussed.

Isoform purification of gastric lipases. Towards crystallization

Several isoforms of rabbit and human gastric lipases have been purified. These isoforms have the same apparent molecular weight (Mr approximately 50,000), but very different isoelectric points. Some of these isoforms were purified: pI 7.2 and 6.5 in the case of rabbit gastric lipase; and pI 7.4 and 7.2 in that of human gastric lipase. All the purified isoforms were found to have the same specific lipase activity (around 1200 units per mg of protein, measured on tributyrin as substrate). The isoforms of dog gastric lipase are more closely related, and could not be separated. Partial enzymatic deglycosylation of human gastric lipase reduced the apparent molecular weight from Mr approximately 50,000 to Mr approximately 43,000 and induced a change in the isoelectrofocusing pattern and the emergence of a new isoform (pI 7.3). It is concluded that the charge heterogeneity of gastric lipases is at least partly due to the glycan moiety of the molecule, which amounts to approximately 14% of the total molecular weight. Several crystallization trials on purified native preparations of rabbit and human gastric lipases were unsuccessful, whereas crystals were obtained from native dog gastric lipase and all the purified isoforms of rabbit and human gastric lipases, some of which were crystallographically characterized.

Molecular cloning and physical analysis of an 8.2 kb segment of chromosome XI of Saccharomyces cerevisiae reveals five tightly linked genes

The nucleotide sequence of 6472 base pairs of an 8.2 kb segment of Saccharomyces cerevisiae chromosome XI has been determined. The sequence contains a cluster of four long open reading frames (ORF) designated YKL2, YKL3, YKL4 and TGL1 in the same orientation, flanked at the 5'-end by a divergent incomplete ORF (YKL1). Transcription and Southern analysis of the four complete ORFs showed that all are expressed and are present in single copy on the haploid genome. The average codon adaptation index of the coding regions is approximately 0.2, suggesting that these genes are lowly expressed. The upstream regions of all four genes as well as the YKL1 ORF contain putative promoter elements previously found to be characteristic of nuclear genes encoding mitochondrial proteins. Significant sequence similarities were found between the YKL3 protein and Escherichia coli ribosomal protein S2 as well as between the TGL1 protein and triglyceride lipases from rat salivary gland and human gastric tissue. The 3'-end of the 6472 bp nucleotide sequence overlaps with the upstream region of the previously identified CTK1 gene, encoding the largest subunit of CTD kinase (Lee, J.M. and Greenleaf, A.L., 1991, Gene Expression 2, 149-167), thereby increasing the number of genes on the 8.2 kb fragment to at least five. The transcripts of these genes represent approximately 83% of the DNA fragment, making it one of the most highly transcribed regions of the yeast chromosome analysed to date.

Nucleotide sequence analysis reveals linked N-acetyl hydrolase, thioesterase, transport, and regulatory genes encoded by the bialaphos biosynthetic gene cluster of Streptomyces hygroscopicus

Nucleotide sequence analysis of a 5,000-bp region of the bialaphos antibiotic production (bap) gene cluster defined five open reading frames (ORFs) which predicted structural genes in the order bah, ORF1, ORF2, and ORF3 followed by the regulatory gene, brpA (H. Anzai, T. Murakami, S. Imai, A. Satoh, K. Nagaoka, and C.J. Thompson, J. Bacteriol. 169:3482-3488, 1987). The four structural genes were translationally coupled and apparently cotranscribed from an undefined promoter(s) under the positive control of the brpA gene product. S1 mapping experiments indicated that brpA was transcribed by two promoters (brpAp1 and brpAp2) which initiate transcription 150 and 157 bp upstream of brp A within an intergenic region and at least one promoter further upstream within the bap gene cluster (brpAp3). All three transcripts were present at low levels during exponential growth and increased just before the stationary phase. The levels of the brpAp3 band continued to increase at the onset of stationary phase, whereas brpAp1-and brpAp2-protected fragments showed no further change. BrpA contained a possible helix-turn-helix motif at its C terminus which was similar to the C-terminal regulatory motif found in the receiver component of a family of two-component transcriptional activator proteins. This motif was not associated with the N-terminal domain conserved in other members of the family. The structural gene cluster sequenced began with bah, encoding a bialaphos acetylhydrolase which removes the N-acetyl group from bialaphos as one of the final steps in the biosynthetic pathway. The observation that Bah was similar to a rat and to a bacterial (Acinetobacter calcoaceticus) lipase probably reflects the fact that the ester bonds of triglycerides and the amide bond linking acetate to phosphinothricin are similar and hydrolysis is catalyzed by structurally related enzymes. This was followed by two regions encoding ORF1 and ORF2 which were similar to each other (48% nucleotide identity, 31% amino acid identity), as well as to GrsT, a protein encoded by a gene located adjacent to gramicidin S synthetase in Bacillus brevis, and to vertebrate (mallard duck and rat) thioesterases. The amino acid sequence and hydrophobicity profile of ORF3 indicated that it was related to a family of membrane transport proteins. It was strikingly similar to the citrate uptake protein encoded by the transposon Tn3411.

Milk lipid digestion in the neonatal dog: the combined actions of gastric and bile salt stimulated lipases

Intragastric lipolysis may be particularly important for the digestion of milk lipid since milk fat globules are resistant to pancreatic lipase without prior disruption; milk bile salt stimulated lipase (BSSL) may supplement further intestinal hydrolysis. Previous information on gastric lipolysis has been based primarily on in vitro studies using artificial lipid emulsions containing a single component fatty acid and have focused on the preferential release of medium-chain fatty acids. The actual contribution of these enzymes to overall fat digestion in vivo on natural substrates has rarely been studied, however. The neonatal dog is an excellent model in the study of lipid digestion because, like the human, milk lipids are high in long-chain unsaturated fatty acids, milk contains BSSL and gastric lipase is the predominant lipolytic enzyme acting in the stomach. We used a combination of in vivo studies with in vitro incubations to investigate digestion of milk lipid by gastric and milk (BSSL) lipases in the suckling dog. In the first 4 weeks postpartum, 14-41% and 42-60% of milk triacylglycerol was hydrolyzed to primarily diacylglycerol and free fatty acid (FFA) in the first 30 and 60 min in the stomach, respectively. Milk lipid contained high levels (63%) of long-chain unsaturated fatty acids, which were preferentially released as FFA during in vivo gastric lipolysis, consistent with the actions and stereospecificity of gastric lipase. While levels of hydrolysis in gastric aspirates were significantly different (by age and time in stomach) at the start of in vitro studies, total hydrolysis in all incubation systems plateaued at about 65%, suggesting product inhibition by the long-chain FFA, but to a much lesser degree than previously expected from in vitro studies. The magnitude of in vivo intragastric lipolysis was 3- to 6-times greater than that predicted by in vitro assays using either milk lipid or labeled emulsion as substrate, respectively. Prior exposure to intragastric lipolysis resulted in 30% hydrolysis by BSSL compared to 5% hydrolysis without prior exposure. We suggest that previous in vitro studies have largely underestimated the actual degree of intragastric lipolysis that can occur and its activity on long-chain fatty acids; this study indicates the importance of the combined mechanisms of gastric lipase and BSSL to fat digestion in the suckling neonate.

Interactions of lipases with lipid monolayers. Facts and questions

Among the proteins, lipolytic enzymes provide a valuable model for studying protein-lipid interactions. Lipases having a catalytic action which is strictly dependent upon the presence of a lipid interface were used in the present study in order to gain better insight into protein-lipid interactions. Most of the data presented here were obtained using the monolayer technique, by recording (either independently or simultaneously) the lipolytic activity, the amount of protein adsorbed to the lipid monolayer, and the surface pressure variations following protein adsorption. Several non-enzymatic proteins were used as controls in order to determine how lipase behaviour differs from that of other proteins. At all initial surface pressures tested, with zwitterionic monolayers, a good correlation was observed between the amount of lipase bound to the monolayer and the surface pressure increase, in agreement with previous studies. Conversely, with neutral lipid monolayers the amount of lipase bound to the monolayer was not found to be surface pressure dependent. This latter behaviour observed with lipases on neutral films is not specific to lipases, since it was also observed with bovine serum albumin and beta-lactoglobulin A. Lipase activity in the presence of various proteins was investigated with monomolecular films of glycerol didecanoate, either at constant surface area or at constant surface pressure. Depending upon the nature of the lipase and the protein, inhibition of lipase activity was either observed or not. Inhibition was correlated with a decrease in lipase surface concentration. The ability of the various proteins to inhibit lipolysis is: (i) a function of their excess versus lipase in the bulk phase, and: (ii) correlated with their penetration capacity (i.e., the initial rate of surface pressure increase of a glycerol didecanoate monolayer having an initial surface pressure of 20 dyn/cm, after the injection-of the protein). Since lipase inhibition was observed with low surface densities of inhibitory proteins, a long-range effect is probably involved in the mechanism of interfacial lipase inhibition. The nature of the ionic charge added to the monolayer by the protein is not critical for determining lipase adsorption or desorption. It is hypothesized that the lack of lipase adsorption to, or desorption from, the lipid monolayer results from a change in the organization of the hydrocarbon moiety of the lipid.

A serine protease triad forms the catalytic centre of a triacylglycerol lipase

True lipases attach triacylglycerols and act at an oil-water interface; they constitute a ubiquitous group of enzymes catalysing a wide variety of reactions, many with industrial potential. But so far the three-dimensional structure has not been reported for any lipase. Here we report the X-ray structure of the Mucor miehei triglyceride lipase and describe the atomic model obtained at 3.1 A resolution and refined to 1.9 A resolution. It reveals a Ser..His..Asp trypsin-like catalytic triad with an active serine buried under a short helical fragment of a long surface loop.