Gastrin-binding Protein Research Articles

Molecular Complementarity III. Peptide Complementarity as a Basis for Peptide Receptor Evolution: A Bioinformatic Case Study of Insulin, Glucagon and Gastrin

Dwyer has suggested that peptide receptors evolved from self-aggregating peptides so that peptide receptors should incorporate regions of high homology with the peptide ligand. If one considers self-aggregation to be a particular manifestation of molecular complementarity in general, then it is possible to extend Dwyer's hypothesis to a broader set of peptides: complementary peptides that bind to each other. In the latter case, one would expect to find homologous copies of the complementary peptide in the receptor. Thirteen peptides, 10 of which are not known to self-aggregate (amylin, ACTH, LHRH, angiotensin II, atrial natriuretic peptide, somatostatin, oxytocin, neurotensin, vasopressin, and substance P), and three that are known to self-aggregate (insulin, glucagon, and gastrin), were chosen. In addition to being self-aggregating, insulin and glucagon are also known to bind to each other, making them a mutually complementary pair. All possible combinations of the 13 peptides and the extracellular regions of their receptors were investigated using bioinformatic tools (a total of 325 combinations). Multiple, statistically significant homologies were found for insulin in the insulin receptor; insulin in the glucagon receptor; glucagon in the glucagon receptor; glucagon in the insulin receptor; and gastrin in gastrin binding protein and its receptor. Most of these homologies are in regions or sequences known to contribute to receptor binding of the respective hormone. These results suggest that the Dwyer hypothesis for receptor evolution may be generalizable beyond self-aggregating to complementary peptides. The evolution of receptors may have been driven by small molecule complementarity augmented by modular evolutionary processes that left a “molecular paleontology” that is still evident in the genome today. This “paleontology” may allow identification of peptide receptor sites.

Identification of a 70-kDa gastrin-binding protein on DLD-1 human colorectal carcinoma cells

Gastrin 17gly acts as a growth factor for the colonic mucosa. Studies of the receptor involved have generally been restricted to its binding properties, and no investigation of the structure of gastrin 17gly receptors on human colorectal carcinoma cell lines has yet been reported. The aim of this study was to optimise the conditions for binding of gastrin 17gly to the human colorectal carcinoma cell line DLD-1, and to investigate the structure of the receptor responsible. Binding of 125I[Met 15]gastrin 17gly to DLD-1 cells was measured in competition experiments with increasing concentrations of either gastrin 17gly or gastrin 17, or with single concentrations of gastrin receptor antagonists. The molecular weights of the gastrin 17gly binding proteins were determined by gel electrophoresis and autoradiography after covalent cross-linking of 125I[Nle 15]gastrin 2,17gly to cells or membranes with disuccinimidyl suberate. The IC 50 value for binding of gastrin 17gly to DLD-1 cells was 2.1±0.4 μM. Binding was inhibited by the non-selective gastrin/cholecystokinin receptor antagonists proglumide and benzotript, but not by the cholecystokinin-A receptor antagonist L364,718, or the gastrin/cholecystokinin-B receptor antagonist L365,260. The molecular weight of the major gastrin binding protein on DLD-1 cells or membranes was 70,000. We conclude that the major gastrin 17gly binding site on the human colorectal carcinoma cell line DLD-1 is clearly distinct from the cholecystokinin-A and gastrin/cholecystokinin-B receptors, but is similar in some respects to the gastrin/cholecystokinin-C receptor.

Mutation of lysine residues of the 78-kDa gastrin-binding protein reduces gastrin binding.

The 78-kDa gastrin-binding protein (GBP) is a likely target for the antiproliferative effects of gastrin/cholecystokinin receptor antagonists on colorectal carcinoma cell lines. Both the N- and C-terminal halves of the GBP bind gastrin, but the affinity of the N-terminal half for gastrin is 7.2-fold higher than the affinity of the C-terminal half. In order to define the gastrin-binding sites of the GBP in greater detail, we have constructed a truncation mutant lacking residues 221-318 of the N-terminal domain and a series of point mutants in which the lysine residues in the first 220 residues of the N-terminal domain were mutated to arginine residues. The effect of these mutations on both the extent of covalent cross-linking of iodinated gastrin2,17 and on the affinity for gastrin17 was investigated. Deletion of residues 221-318 of the GBP decreased the affinity 5.5-fold and reduced, but did not abolish, the extent of covalent cross-linking. Mutation of the 17 lysines in residues 1-220 of the GBP decreased the affinity for gastrin between 1.7- and 3.5-fold and in some cases reduced, but did not abolish, the extent of covalent cross-linking. We conclude that one or more lysine residues are involved in binding of gastrin to the GBP, but that no single lysine residue is the preferred target for covalent cross-linking of iodinated gastrin2,17 to the GBP.

Inhibition of the preferential binding of actin to the N-terminal hydratase domain of the 78-kDa gastrin-binding protein by non-steroidal anti-inflammatory drugs and gastrin receptor antagonists

The 78 kDa gastrin-binding protein (GBP) is a likely target for the antiproliferative effects of gastrin receptor antagonists and non-steroidal anti-inflammatory drugs (NSAIDs) on colorectal carcinoma cells (Baldwin GS, Murphy VJ, Yang Z, and Hashimoto T. J Pharmacol Exp Ther 1998;286:1110–14). This study tested the hypotheses that the GBP bound actin, and that the interaction could be disrupted by gastrin receptor antagonists and NSAIDs. Binding of actin to the GBP was assessed by competition with 125I-[Nle 15]-gastrin 2,17 in a covalent cross-linking assay, and by comparison of 125I-actin binding to the N- and C-terminal GBP domains, which had been expressed independently in E. coli as glutathione-S-transferase (GST) fusion proteins. The ability of gastrin receptor antagonists and NSAIDs to interfere with the actin-GBP interaction was measured by release of 125I-actin from preformed complexes with the N- and C-terminal domain-GST fusion proteins. Actin purified from skeletal muscle or from gastric mucosal cytosol competed with 125I-[Nle 15]-gastrin 2,17 for binding to the GBP with ic 50 values of 2.6 ± 0.7 μM, and 2.1 ± 0.7 μM, respectively. The amount of 125I-actin from either source bound to the N-terminal GBP domain was 8.2 times greater than the amount bound to the C-terminal domain. Binding of actin to both domains was inhibited by the gastrin receptor antagonists proglumide and benzotript, and by NSAIDs. We conclude that the GBP may associate with the cytoskeleton via an interaction between its N-terminal domain and actin, and that the association may be disrupted either by gastrin receptor antagonists or by NSAIDs.

Retinoic acid-induced apoptotic pathway in T-cell lymphoma: Identification of four groups of genes with differential biological functions.

Retinoic acid (RA) has been used to induce the regression of refractory T-cell lymphoma. In vitro and in vivo studies have shown that RA exerts this effect through the induction of apoptosis. This study was designed to investigate the molecular pathway of RA-induced apoptosis in T-lymphoma cell lines.RA-induced apoptosis was verified by morphology, flow cytometry, and DNA ladder analysis. Differential display method using a combination of 12 poly(A)-anchored primers and 20 arbitrary primers was adopted for gene cloning. Total RNAs were extracted from H9 cell line at 0, 6, 12, and 24 hours after All-trans RA (ATRA) treatment and the serial expression patterns of the candidate fragments were recognized. The cloned gene fragments were then analyzed and confirmed by Northern blot analysis on H9 and SR786 cell lines.ATRA-induced apoptosis of T-cell lymphoma was protein synthesis-dependent. The execution or irreversible phase of apoptosis appeared to occur at 6-12 hours of RA treatment. Among the 60,000 arbitrarily displayed bands, 25 of 250 candidate fragments were selected for further cloning and sequencing. A total of 14 clones could be matched to known genes and were categorized into four groups: A) transcription factors: prothymosin, CA150, p78 serine/threonine kinase, IL-1beta-stimulating gene, glucocorticoid receptor, MLN64/CAB1, gastrin-binding protein, and polypeptide from glioblastoma; B) chaperone: 90 kDa heat shock protein; C) ion channel: chloride channel protein 3; and D) cytoskeleton: cytovillin2/ezrin and vimentin. Another two clones of genes were of unrecognized functions. The remaining 11 clones belonged to unmatched or novel genes. The expression of these genes varied, either upregulated or downregulated, in response to ATRA treatment.RA-induced apoptosis may involve a cascade of genes that are related to transcription regulation, stress response, housekeeping, and the execution of apoptosis. The clarification of the RA-induced apoptotic pathway will help us to understand the molecular mechanism of cancer differentiation agents.

Affinity of cholecystokinin receptor antagonists for the gastrin-binding protein

A 78 kDa gastrin-binding protein is a likely target for the anti-proliferative effects of the cholecystokinin (CCK) receptor antagonists d, l-4-benzamido- N, N-dipropylglutaramic acid (proglumide) and N-4-chlorobenzoyl- l-tryptophan (benzotript) on colorectal carcinoma cell lines [Baldwin, G.S., 1994. Antiproliferative gastrin/cholecystokinin receptor antagonists target the 78-kDa gastrin-binding protein. Proc. Natl. Acad. Sci. USA 91, 7593–7597.]. Definition of the physiological role of the gastrin-binding protein has been hampered by the very low affinity of benzotript for the gastrin-binding protein. Benzotript analogues were therefore tested for their ability to inhibit the binding of iodinated gastrin to the gastrin-binding protein. The affinity of the most potent analogue (the d-isomer of benzotript, CR 665) was similar to the value reported previously for the l-isomer. In order to isolate more potent binding inhibitors, several selective CCK receptor antagonists were also tested as inhibitors of the binding of gastrin to the gastrin-binding protein. The affinity of the most potent binding inhibitor PD 149164 (benzenebutanoic acid, 4-fluoro-!b/-[[3-(1 H-indol-3-yl)-2-methyl-1-oxo-2-[[(tricyclo-[3.3.1.1 3,7]dec-2-yloxy)carbonyl]amino]propyl]amino]-, [ R-( R*, S*)]-) was approximately 10-fold higher than the l-isomer of benzotript. PD 149164 may serve as the lead compound for the future development of more potent and selective gastrin-binding protein inhibitors.

Identification and characterization of an intracellular protein complex that binds fibroblast growth factor-2 in bovine brain

The fibroblast growth factor (FGF) family is composed of polypeptides with sequence identity which signal through transmembrane tyrosine kinase receptors. We report here the purification from bovine brain microsomes of an FGF-2-binding complex composed of three proteins of apparent molecular masses 150 kDa, 79 kDa and 46 kDa. Only the 150 kDa and 79 kDa proteins bound FGF-2 in cross-linking and ligand-blotting experiments. Binding of FGF-2 to p79 is enhanced in the presence of calcium. Peptide sequences allowed the identification of p150 and the cloning of the cDNAs encoding p79 and p46. The deduced amino acid sequence of p79 reveals high similarity to those of gastrin-binding protein and mitochondrial enoyl-CoA hydratase/hydroxyacyl-CoA dehydrogenase. p46 is similar to mitochondrial ketoacyl-CoA thiolase. Stable transfection of FR3T3 rat fibroblast cells with p79 cDNA analysed by electron microscopy following immunolabelling of ultra-thin cryosections revealed a localization of p79 in the secretory pathway, mainly in the endoplasmic reticulum and the Golgi region, where it is specifically associated with the molecular chaperone calnexin. In vivo a protein similar to the Golgi protein MG-160 forms a complex with FGF-2 and p79.

Identification and characterization of an intracellular protein complex that binds fibroblast growth factor-2 in bovine brain

The fibroblast growth factor (FGF) family is composed of polypeptides with sequence identity which signal through transmembrane tyrosine kinase receptors. We report here the purification from bovine brain microsomes of an FGF-2-binding complex composed of three proteins of apparent molecular masses 150 kDa, 79 kDa and 46 kDa. Only the 150 kDa and 79 kDa proteins bound FGF-2 in cross-linking and ligand-blotting experiments. Binding of FGF-2 to p79 is enhanced in the presence of calcium. Peptide sequences allowed the identification of p150 and the cloning of the cDNAs encoding p79 and p46. The deduced amino acid sequence of p79 reveals high similarity to those of gastrin-binding protein and mitochondrial enoyl-CoA hydratase/hydroxyacyl-CoA dehydrogenase. p46 is similar to mitochondrial ketoacyl-CoA thiolase. Stable transfection of FR3T3 rat fibroblast cells with p79 cDNA analysed by electron microscopy following immunolabelling of ultra-thin cryosections revealed a localization of p79 in the secretory pathway, mainly in the endoplasmic reticulum and the Golgi region, where it is specifically associated with the molecular chaperone calnexin. In vivo a protein similar to the Golgi protein MG-160 forms a complex with FGF-2 and p79.

Structural requirements for the binding of non-steroidal anti-inflammatory drugs to the 78 kDa gastrin binding protein

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit the proliferation of colorectal carcinoma cell lines in vitro and reduce the risk of colorectal carcinoma in vivo. The good correlation observed between the potency of NSAIDs as inhibitors of colorectal carcinoma cell proliferation and as antagonists of a 78 kDa gastrin binding protein (GBP) suggested that blockade of the GBP might contribute to the anti-proliferative effects of NSAIDs [G.S. Baldwin, V.J. Murphy, Z. Yang, T. Hashimoto, J. Pharmacol. Exp. Ther. 286 (1998) 1110–1114]. The most potent NSAID investigated was sulindac sulphide, which had an IC 50 value of 40 μM. In order to investigate the structural requirements for binding to the GBP, 26 analogues of sulindac sulphide and sulindac sulphoxide were tested for their ability to inhibit the binding of iodinated gastrin to the GBP. Six of the analogues inhibited gastrin binding by more than 50% at a concentration of 1 mM. The IC 50 values estimated by computer fitting of titration data were in the range of 280–940 μM. Comparison of the analogue structures suggests that a substituent with a carboxyl group is preferred in the R 2 position. In addition the location of the NSAID binding site within the GBP structure was investigated. NSAIDs bound to both the N- and C-terminal halves of the GBP, and the affinities determined were similar to the values previously reported for the full-length GBP. The results reported herein represent the first step in the rational design of more potent GBP antagonists, some of which may be useful for the treatment of colorectal carcinoma.

Binding of pepsinogen to the 78 kDa gastrin binding protein

An endogenous ligand of the 78 kDa gastrin-binding protein (GBP) has been purified from detergent extracts of porcine gastric mucosal membranes by ion exchange chromatography and preparative gel electrophoresis. The ligand bound to the GBP with high affinity (mean IC 50 value of 0.31±0.09 μg/ml, or 8 nM), as assessed by inhibition of cross-linking of iodinated gastrin 2,17 to the GBP. Both the N- and C-terminal halves of the GBP, which had been expressed individually as glutathione- S-transferase fusion proteins in Escherichia coli, and purified on glutathione–agarose beads, bound the ligand. Two peptides derived from the ligand were purified by reversed-phase high-performance liquid chromatography (HPLC), and characterised by mass spectrometry and Edman sequencing. The peptides were 97% and 100% identical, respectively, to amino acids 119–157 and 199–219 of porcine pepsinogen A. Commercial samples of pepsinogen also bound to the GBP, with a mean IC 50 value of 3.9±1.2 μg/ml (100 nM). We conclude that the ligand is closely related, but not identical, to pepsinogen A.

A Novel Gastrin-Binding Protein in the Human Eosinophil

A specific and saturable interaction between125I-gastrin and eosinophils was discovered in autoradiographs of human gastric mucosal tissue and confirmed in isolated and enriched preparations of WBC's. Gastrin displaced125I-gastrin from eosinophils in a dose-dependent manner with a D50= 11 uM. Scatchard analysis of the saturation curve indicated a single binding site of low affinity (Kd= 4.14 uM) and high capacity (Bmax= 430 umoles/mg protein). The gastrin binding protein was localized to the granular core of the eosinophil and found to have a molecular weight of ∼15 kDa following chemical crosslinking of radioligand to granules and SDS/PAGE. Based on its molecular weight and granular location and the charge characteristics of gastrin, the gastrin binding protein in the human eosinophil is most likely major basic protein.In vivothis interaction might act to limit the cytotoxic potential of MBP on tissues and/or attentuate gastrin concentrations thereby helping regulate gastric acid secretion and mucosal growth.

Widespread tissue expression of gastrin-binding-protein mRNA.

Glycine-extended forms of gastrin (gastrin-Gly) are thought to be involved in the autocrine growth control of colorectal carcinomas. The recently described gastrin-binding protein has been suggested to be a gastrin-Gly accepting receptor. Northern blot analysis demonstrated the expression of gastrin-binding-protein mRNA in many tissues of mouse, rat, and man. The gastrin-binding-protein mRNA expression was confirmed by reverse-transcribed PCR analysis. Analysis of the cDNA and the deduced amino acid sequence of the PCR-amplified rat gastrin-binding-protein DNA fragments revealed sequence identity (except in a single position) with the corresponding human and pig gastrin-binding protein and with the alpha-subunit of a rat and human mitochondrial trifunctional enzyme, involved in fatty acid oxidation. The widespread and abundant tissue expression of gastrin-binding-protein mRNA and its sequence identity with a fatty-acid-oxidizing enzyme do not support the view that it represents a genuine gastrin receptor.

Gastrin and gastrin receptor antagonists bind to both N- and C-terminal halves of the 78 kDa gastrin-binding protein

A 78 kDa gastrin-binding protein (GBP) has previously been identified as the target of the anti-proliferative effects of non-selective gastrin/cholecystokinin receptor antagonists on colorectal carcinoma cell lines. The GBP was related in sequence to a family of fatty acid oxidation enzymes possessing enoyl CoA hydratase and 3-hydroxyacyl CoA dehydrogenase activity. This study aims to define the binding site for gastrin and gastrin antagonists in greater detail. The N- and C-terminal halves of the porcine GBP were expressed independently as glutathione S-transferase fusion proteins in E. coli. Affinities of gastrin and gastrin antagonists for the fusion proteins were measured by competition for 125I-[Nle 15]-gastrin 2,17 binding in a covalent cross-linking assay. The N- and C-terminal fusion proteins bound gastrin 17 with affinities of 9.9 ± 6.1 and 71 ± 48 μM, respectively ( n = 3). These values were 40-fold and 300-fold lower than the affinity of the full-length GBP for gastrin 17 (0.23 ± 0.15 μM). In contrast, the affinities of the N- and C-terminal halves for the antagonists proglumide (22 ± 13 and 10 ± 4 mM, respectively) and benzotript (350 ± 90 and 400 ± 160 μM, respectively) were similar to each other and to the affinities of proglumide and benzotript for the full-length GBP (5.1 ± 3.6 mM and 200 ± 120 μM, respectively). It is concluded that proglumide and benzotript bind independently to both the hydratase and dehydrogenase active sites of the GBP, while a single molecule of gastrin 17 may bind simultaneously to both active sites. A model is proposed which is consistent with these data, and which will assist in the development of more potent and selective GBP antagonists.

A new inhibitor of mitochondrial fatty acid oxidation.

The mitochondrial enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase/3-ketoacyl-CoA thiolase trifunctional protein (trifunctional protein) plays a major role in mitochondrial fatty acid oxidation. The enzyme complex consists of four molecules of alpha-subunit containing both hydratase and dehydrogenase domains and four molecules of beta-subunit containing the thiolase domain. The primary structure of a gastrin-binding protein (GBP) was highly homologous to that of the alpha-subunit of the trifunctional protein. Here, we report that gastrin inhibits the hydratase, dehydrogenase, and thiolase activities of the trifunctional protein. The gastrin/cholecystokinin receptor antagonist benzotript, which inhibited binding of gastrin to the GBP, also inhibited all three activities of the trifunctional protein. In addition, benzotript inhibits the activities of multifunctional enzymes having similar structures, such as the peroxisomal enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase bifunctional protein and the Pseudomonas fragi fatty acid oxidation enzyme complex. This reagent, however, hardly inhibited various monofunctional enzymes involved in fatty acid oxidation.

Binding of progastrin fragments to the 78 kDa gastrin-binding protein

The non-selective gastrin/cholecystokinin receptor antagonists proglumide and benzotript inhibit colon carcinoma cell proliferation by binding to the 78 kDa gastrin-binding protein (GBP) (Baldwin, Proc. Natl. Acad. Sci. USA, 91 (1994) 7593–7597). However, although most colon carcinoma cell lines synthesize progastrin, production of mature amidated gastrin 17 has not been observed. In order to define the structural requirements for the binding of gastrin to the GBP the affinities of various fragments of amidated and C-terminally extended gastrin 17 for the GBP have been measured. The results indicate that the GBP recognizes both N- and C-termini of gastrin 17. Moreover since C-terminal amidation is not a prerequisite for binding of gastrin to the GBP, the GBP is a potential target for the autocrine effects of progastrin.

Structures of the human cDNA and gene encoding the 78 kDa gastrin-binding protein and of a related pseudogene

The nucleotide sequence encoding the human 78 kDa gastrin binding protein (GBP) has been deduced from overlapping fragments generated by the polymerase chain reaction with oligonucleotides based on the sequence of the porcine GBP (Mantamadiotis, T. et al. (1993) Biochim. Biophys. Acta 1170, 211–215) and cDNA from the colonic carcinoma cell line LIM 1215 as template. The mature human GBP is 90% identical to the porcine GBP. Clones encoding the human GBP gene, which contains 19 exons, have been isolated from human genomic libraries. The positions of the exon/intron junctions are completely different from the junctions in the gene encoding the related peroxisomal trifunctional enzyme. Clones encoding a related pseudogene have also been isolated and sequenced.

Antiproliferative gastrin/cholecystokinin receptor antagonists target the 78-kDa gastrin-binding protein.

Inhibition of colon carcinoma cell growth by the nonselective gastrin/cholecystokinin (CCK) receptor antagonists proglumide and benzotript provided evidence that gastrin functions as an autocrine growth factor. However, the molecular properties of the receptor mediating the antagonist effects have not been identified. A 78-kDa gastrin-binding protein (GBP), the sequence of which is related to the family of enzymes possessing enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase activities, has been previously purified from porcine gastric mucosal membranes. I now report that covalent cross-linking of 125I-labeled [Nle15]gastrin2,17 to the 78-kDa GBP is inhibited by crotonyl-CoA and by acetoacetyl-CoA. Gastrin, CCK, and their analogues also inhibit cross-linking, and the spectrum of analogue affinities correlates better with the values previously reported for binding to the gastrin/CCK-C receptor than with the values reported for binding to either the CCK-A or the gastrin/CCK-B receptor. Cross-linking is also inhibited by proglumide and benzotript, but no inhibition is seen with either the CCK-A receptor-selective antagonist L364,718 or the gastrin/CCK-B receptor-selective antagonist L365,260. The affinities of antagonists for the GBP correlate well with their affinities for the gastrin/CCK-C receptor and with their potencies for inhibition of colon carcinoma cell growth. I conclude that the 78-kDa gastrin-binding protein is (i) a member of the hydratase/dehydrogenase family of fatty acid oxidation enzymes, (ii) the gastrin/CCK-C receptor, and (iii) the target for the antiproliferative action of two gastrin/CCK receptor antagonists.

Isolation and partial amino acid sequence of A 78 kDa porcine gastrin-binding protein

1. 1. A 78 kDa protein (p78) has been partially purified from washed membranes isolated from the corpus of porcine gastric mucosa. The purification was monitored by covalent cross-linking of iodinated [Nle 15]-gastrin; 17. 2. 2. A single N-terminal sequence extending for 33 amino acids was obtained from the p78 preparation. Partial sequences totalling 192 amino acids were also obtained from 14 tryptic and 3 Staphylococcal V8 peptides. 3. 3. 10 peptides plus the N-terminal sequence were derived from a previously unsequenced protein which was distantly related to the product of the E. coli fadB gene (Baldwin G. S. (1993) Comp. Biochem. Physiol. 104B, 55–61). The remaining 7 peptides were derived from the gb-subunit of the gastric H +/K +-ATPase. 4. 4. The gastrin-binding activity remained in association with p78, and could be separated from the P-subunit of the gastric H +K +-ATPase, during chromatography on tomato lectin-Sepharose. 5. 5. We conclude that p78 binds gastrin, and is a novel member of the enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase family of enzymes.

Primary Structure of the Large Subunit of Trifunctional β-Oxidation Complex from Pig Heart Mitochondria

The amino-terminal and internal sequences of the isolated large subunit of trifunctional β-oxidation complex from pig heart mitochondria were determined by Edman degradation. The results demonstrated that the sequence of this novel β-oxidation enzyme is identical with the sequence recently reported for a porcine gastrin binding protein that serves as the gastrin receptor on parietal cell surfaces. Evidence is provided to show that it is unlikely that the porcine gastrin binding protein has such a sequence. The data lead us to conclude that the mature large subunit of porcine trifunctional β-oxidation complex is composed of 727 amino acid residues with a calculated molecular weight of 79,113, while the precursor of this long-chain fatty acid oxidation enzyme has a mitochondrial presequence consisting of 36 residues and a calculated Mr of 83,099.

Nucleotide sequence encoding a novel member of the hydratase/dehydrogenase family

The nucleotide sequence encoding a novel member of the family of fatty acid oxidation enzymes has been determined. Clones were generated from porcine gastric corpus cDNA by application of the polymerase chain reaction (PCR) using oligodeoxyri-bonucleotides based on the amino acid sequence of a 78 kDa gastrin-binding protein isolated from porcine gastric mucosal membranes (Baldwin et al., J. Biol. Chem. 261 (1986) 12252–12257). Clones encoding the 3' and 5' ends of the cDNA were then isolated by conventional screening of a porcine liver cDNA library, and by application of anchored PCR, respectively. The composite cDNA of 2744 nucleotides encoded a protein of 763 amino acids, the sequence of which was related to a rat peroxisomal trifunctional enzyme, Δ 3, Δ 2-enoyl-CoA isomerase/enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase, and to other members of the same enzyme family. Northern blots indicated that the 3-kb mRNA encoding the novel protein was abundant in gastric corpus and liver, with lower amounts also present in gastric antrum and forestomach.