Molecular cloning and primary structure analysis of porcine pancreatic alpha-amylase.

A cDNA library was constructed in a Uni-ZAP XR vector using mRNA isolated from porcine pancreas. A full-length alpha-amylase cDNA was obtained using a combination of library screening and nested polymerase chain reaction. Sequencing of the clone revealed a 1536-nucleotide (nt) open reading frame encoding a protein of 496 amino acid (aa) residues with a signal peptide of 15 aa. The calculated molecular mass of the enzyme was 55354 Da, in accordance with those of the purified porcine pancreatic alpha-amylase forms (PPAI and PPAII) as determined by mass spectrometry. A comparison of the deduced aa sequence with published peptidic sequences of PPAI identified a number of mismatches. The sequence of the cDNA reported here provides a sequence reference for PPA in excellent agreement with the refined three-dimensional structures of both PPAI and PPAII. No evidence for a second variant was found in the cDNA library and it is most likely that PPAI and PPAII are two forms of the same protein. The primary structure of PPA shows high homology with human, mouse and rat pancreatic alpha-amylases. The 304-310 region, corresponding to a mobile loop involved in substrate binding and processing near the active site, is fully conserved.

Comparison of barley malt alpha-amylase isozymes 1 and 2: construction of cDNA hybrids by in vivo recombination and their expression in yeast.

Germinating barley produces two alpha-amylase isozymes, AMY1 and AMY2, having 80% amino acid (aa) sequence identity and differing with respect to a number of functional properties. Recombinant AMY1 (re-AMY1) and AMY2 (re-AMY2) are produced in yeast, but whereas all re-AMY1 is secreted, re-AMY2 accumulates within the cell and only traces are secreted. Expression of AMY1::AMY2 hybrid cDNAs may provide a means of understanding the difference in secretion efficiency between the two isozymes. Here, the efficient homologous recombination system of the yeast, Saccharomyces cerevisiae, was used to generate hybrids of barley AMY with the N-terminal portion derived from AMY1, including the signal peptide (SP), and the C-terminal portion from AMY2. Hybrid cDNAs were thus generated that encode either the SP alone, or the SP followed by the N-terminal 21, 26, 53, 67 or 90 aa from AMY1 and the complementary C-terminal sequences from AMY2. Larger amounts of re-AMY are secreted by hybrids containing, in addition to the SP, 53 or more aa of AMY1. In contrast, only traces of re-AMY are secreted for hybrids having 26 or fewer aa of AMY1. In this case, re-AMY hybrid accumulates intracellularly. Transformants secreting hybrid enzymes also accumulated some re-AMY within the cell. The AMY1 SP, therefore, does not ensure re-AMY2 secretion and a certain portion of the N-terminal sequence of AMY1 is required for secretion of a re-AMY1::AMY2 hybrid.

Isozyme hybrids within the protruding third loop domain of the barley alpha-amylase (beta/alpha)8-barrel. Implication for BASI sensitivity and substrate affinity.

Barley alpha-amylase isozymes AMY1 and AMY2 contain three structural domains: a catalytic (beta/alpha)8-barrel (domain A) with a protruding loop (domain B; residues 89-152) that binds Ca2+, and a small C-terminal domain. Different parts of domain B secure isozyme specific properties as identified for three AMY1-AMY2 hybrids, obtained by homeologous recombination in yeast, with crossing-over at residues 112, 116, and 144. The AMY1 regions Val90-Thr112 and Ala145-Leu161 thus confer high affinities for the substrates alpha-D-maltoheptaoside and amylose, respectively. Leu117-Phe144, and to a lesser degree Ala145-Leu161, are critical for the stability at low pH characteristic of AMY1 and for the sensitivity to barley alpha-amylase/subtilisin inhibitor specific to AMY2.

Bovine pancreatic preproelastases I and II: comparison of nucleotide and amino acid sequences and tissue specific expression.

Clones encoding bovine preproelastases I and II were isolated from a pancreatic cDNA library and were sequenced in order to define the structural characteristics of these enzymes. The bovine 947- and 884-nucleotide preproelastase I and II cDNAs encode proteins containing a signal peptide of the same length (16 amino acids), but with a slightly different number of amino acids for the activation peptide (10 and 12, respectively) and the mature enzyme (240 and 241, respectively). Considering amino acid sequences, each enzyme shares a high degree of identity (76-86%) within species. In contrast, only 55.3% identity is found between bovine elastases I and II. This difference could explain partly their own specificity. Analysis of the expression of the elastases in various bovine tissues demonstrated that they are specifically expressed in high levels in the pancreatic gland. These two approaches (structure and expression) allowed us to characterize the bovine pancreatic elastases I and II.

Antigen specificity and cross-reactivity of fifteen monoclonal antibodies against porcine pancreatic alpha-amylase II and its AB and C domains.

Highly productive hybridoma secreting mabs specific for porcine alpha-pancreatic amylase II were established. Fifteen clones were selected. The mabs produced (KD = 1.68-11.2 nM) were checked for cross-reactivity with six heterologous antigens, namely porcine pancreatic alpha-amylase I, barley amylase, human pancreatic alpha-amylase, Taka amylase and triose phosphate isomerase, using direct ELISA assay; mabs were classified within seven groups: in a few groups mabs cross-reacted with a single heterologous antigen either porcine pancreatic amylase I (6 mabs) or barley amylase (2 mabs) or human pancreatic amylase (3 mabs). Two other groups cross-reacted with two heterologous antigen either porcine I and human or porcine I and barley. Only one mab out of fifteen cross-reacted in direct ELISA binding to all amylases and triose phosphate isomerase. Using sandwich ELISA test only three mabs were found to bind porcine amylase II present at high concentration. Results consistent with direct porcine amylase binding were obtained from binding inhibition assays. Analysis by the additivity test allowed to find that 3 mabs, B10.10, B1.11, C6.4 recognize distinct epitopes while the epitopes for the other pairs tested are either overlapping or at least close to each other. Finally mabs binding specifically either to the AB or to the C domain fragment or to both fragments have been obtained.

Stability of the mRNA encoding some pancreatic hydrolases is modulated by dietary protein intake in the rat.

Wistar rats fed on either a high-protein or a protein-free diet were examined to determine their pancreatic hydrolase mRNA stabilities in comparison with those of control animals receiving a standard diet. Actinomycin D was used to inhibit transcription and, after isolating the pancreatic RNA, the specific messengers were quantified by performing dot-blot hybridization with cDNA probes. In the rats fed on a high-protein diet, only the half-lives of anionic trypsinogen I and elastase I (EC 3.4.21.36) were affected. Interestingly, when rats were fed on the protein-free diet, most of the hydrolase mRNA half-lives showed changes, except that corresponding to lipase. In these rats, the half-life values of the mRNA coding for anionic trypsinogen I, chymotrypsinogen and procarboxypeptidase B increased, in sharp contrast with those of the amylase and elastase I mRNA, which decreased. These results strongly suggest that the mechanism whereby the biosynthesis of pancreatic hydrolases is regulated, depending on the presence or absence of proteins in the diet, is not unique and provide evidence that the stability of mRNA encoding most, if not all, the hydrolases in pancreatic cells is modulated by the dietary protein content.

Dietary modulation of the mRNA stability of trypsin isozymes and the two forms of secretory trypsin inhibitor in the rat pancreas.

The stability of the mRNAs encoding pancreatic trypsin isozymes, namely the cationic form and the two anionic forms I and II, as well as that of the secretory trypsin inhibitors I and II, were studied in rats fed on either a high-protein diet, or a protein-free diet compared with a standard diet for a 10-day period. Either immediately or 3 h and 6 h after injecting the transcription inhibitor, actinomycin D, the mRNA levels were quantified by performing dot-blot hybridization with specific oligonucleotide probes. Under high-protein dietary conditions, the stability of the mRNAs coding for anionic trypsin II and cationic trypsin showed no change, whereas that of anionic trypsin I and the two forms of secretory trypsin inhibitor were affected. The mRNA half-life of anionic trypsin I and trypsin inhibitor II increased, in sharp contrast with that of trypsin inhibitor I, which decreased. When rats were fed on a protein-free diet, the stabilities of both anionic trypsin forms and trypsin inhibitor I increased, whereas that of trypsin inhibitor II decreased and that of cationic trypsin remained unchanged. The present results show the existence of differences in the mechanisms whereby gene expression of trypsin isozymes and secretory trypsin inhibitors is regulated, although they are synthesized in parallel in the pancreatic acinar cell and stored in zymogen granules before being secreted into the intestinal lumen.

Differential splicing and alternative polyadenylation generates distinct NCAM transcripts and proteins in the mouse.

The neural cell adhesion molecule (NCAM) exists in at least three different protein isoforms which are selectively expressed by different cell types and at different stages of development. They are encoded by four to five different transcripts that are derived from a single gene. Here we report the exon--intron structure of the 3' part of the mouse NCAM gene. This region contains six exons. The 5' exon is constitutively expressed in all four prominent size classes of NCAM mRNAs detected in the mouse brain. The second exon contains the poly(A) addition sites for the two smaller mRNAs of 5.2 and 2.9 kb which differ in the length of their 3' non-coding regions and seem both to encode NCAM-120. This second exon is absent in the largest 7.4 kb transcript which encodes NCAM-180; in the 6.7 kb mRNA, which appears to code for NCAM-140, the second and the fifth exon have been spliced out. This data explains how the prominent four transcripts and three protein isoforms of mouse NCAM are generated from a single gene. The alternatively spliced fifth exon is surrounded by inverted repeats potentially capable of secondary structure formation, that may sequester this exon in a loop.

Phosphatidylinositol is involved in the membrane attachment of NCAM-120, the smallest component of the neural cell adhesion molecule.

The rodent neural cell adhesion molecule (NCAM) consists of three glycoproteins with Mr of 180,000, 140,000 and 120,000. The Mr 120,000 protein (NCAM-120) has been shown to exist in membrane-bound and soluble forms but the nature of its membrane association and release has remained obscure. We show here that phosphatidylinositol-specific phospholipase C (PI-PLC), but not a phospholipase C of different specificity, releases a substantial proportion of NCAM-120 from brain membranes and solubilizes almost quantitatively NCAM-120 present at the surface of C6 astroglial cells. The PI-PLC effect was highly selective since only one other protein species was detectably released from C6 cells. These results suggest that NCAM-120 is held in the membrane by covalently bound phosphatidylinositol or a closely related lipid in a way similar to several other surface proteins from eukaryotic cells. The presence of NCAM in a form which can be released from the cell surface by a highly selective mechanism raises additional possibilities for modulation and control of cell--cell adhesion.

Domain B protruding at the third beta strand of the alpha/beta barrel in barley alpha-amylase confers distinct isozyme-specific properties.

alpha-Amylases belong to the alpha/beta-barrel protein family in which the active site is created by residues located at the C-terminus of the beta strands and in the helix-connecting loops extending from these ends. In the alpha-amylase family, a small separate domain B protrudes at the C-terminus of the third beta strand of the (beta/alpha)8-barrel framework. The 80% identical barley alpha-amylase isozymes 1 and 2 (AMY1 and AMY2, respectively) differ in substrate affinity and turnover rate, CaCl2 stimulation of activity, sensitivity to the endogenous 21-kDa alpha-amylase/subtilisin inhibitor, and stability at low pH. To identify regions that confer these isozyme-specific variations, AMY1-AMY2 hybrid cDNAs were generated by in vivo homologous recombination in yeast. The hybrids AMY1-(1-90)-AMY2-(90-403) and AMY1-(1-161)-AMY2-(161-403) characterized in this study contain the 90-residue and 161-residue N-terminal sequences, respectively, of AMY1 and complementary C-terminal regions of AMY2. AMY1-(1-90)-AMY2-(90-403) comprises the 60-amino-acid domain B of AMY2 and resembles this isozyme in sensitivity to alpha-amylase/subtilisin inhibitor and its low affinity for the substrates p-nitrophenyl alpha-D-maltoheptaoside, amylose and the inhibitor acarbose. Only AMY1-(1-161)-AMY2-(161-403) and AMY1, which both share domain B, are stable at low pH. However, AMY2 and both hybrid AMY species, but not AMY1, show maximum enzyme activity on insoluble blue starch at approximately 10 mM CaCl2. Domain B thus determines several functional and stability properties that distinguish the barley alpha-amylase isozymes.

High-level production of recombinant fungal endo-beta-1,4-xylanase in the methylotrophic yeast Pichia pastoris.

Efficient production of recombinant Aspergillus niger family 11 1, 4-beta-xylanase was achieved in Pichia pastoris. The cDNA-encoding XylA fused to the Saccharomyces cerevisiae invertase signal peptide was placed under the control of the P. pastoris AOX1 promoter. Secretion yields up to 60 mg/liter were obtained in synthetic medium. The recombinant XylA was purified to homogeneity using a one-step purification protocol and found to be identical to the enzyme overexpressed in A. niger with respect to size, pI, and immunoreactivity. N-terminal sequence analysis of the recombinant protein indicated that the S. cerevisiae signal peptide was correctly processed in P. pastoris. The purified protein has a molecular weight of 19,893 Da, in excellent agreement with the calculated mass, and appears as one single band on isoelectric focusing with pI value around 3.5. Electrospray ionization mass spectrometry confirmed the presence of one major isoform produced by P. pastoris and the absence of glycosylation. The recombinant enzyme was further characterized in terms of specific activity, pH profile, kinetic parameters, and thermostability toward birchwood xylan as substrate and compared with the xylanase purified from A. niger. Both enzymes exhibit a pH optimum at 3.5 and maximal activity at 50 degrees C. The enzyme activity follows normal Michaelis-Menten kinetics with K(m) and V(max) values similar for both enzymes. P. pastoris produced recombinant xylanase in high yields that can be obtained readily as a single form. A. niger xylanase is the first microbial xylanase efficiently secreted and correctly processed by P. pastoris.

Cloning, sequencing and functional expression of a cDNA encoding porcine pancreatic preprocarboxypeptidase A1.

A full-length cDNA clone coding for porcine pancreatic preprocarboxypeptidase A1 (prePCPA1) was isolated from a cDNA library. The open reading frame (ORF) of the nucleotide sequence was 1260 nt in length and encoded a protein of 419 amino acids (aa). The cDNA included a short signal peptide of 16 aa and a 94 aa-long activation segment. The calculated molecular mass of the mature proenzyme was 45561 Da, in accordance with that of the purified porcine pancreatic PCPA1. The deduced aa sequence of the corresponding enzyme differed from that predicted by the three-dimensional structure by 40 aa, and showed 85% identity and 55% identity to that of procarboxypeptidases A1 and A2, respectively. Moreover the sequence was identical to that of several independent cDNA clones, suggesting that it is the major transcribed gene. No evidence for a second variant was observed in the cDNA library and PCPA2 is apparently absent from the porcine pancreas. The cDNA was expressed in Saccharomyces cerevisiae under the control of the yeast triose phosphate isomerase promoter. The signal peptide of the PCPA protein efficiently directed its secretion into the culture medium (1.5 mg.L-1) as a protein of the predicted size. The recombinant proenzyme was analyzed by immunological and enzymological methods. Its activation behavior was comparable with that of the native form and led to a 35-kDa active enzyme.

Isolation and nucleotide sequence of mouse NCAM cDNA that codes for a Mr 79,000 polypeptide without a membrane-spanning region.

The neural cell adhesion molecule (NCAM) exists in several isoforms which are selectively expressed by different cell types and at different stages of development. In the mouse, three proteins with apparent Mr's of 180,000, 140,000 and 120,000 have been distinguished that are encoded by 4-5 different mRNAs. Here we report the full amino acid sequence of a NCAM protein inferred from the sequences of overlapping cDNA clones. The 706-residue polypeptide contains, towards its N-terminus, 5 domains that share structural homology with members of the immunoglobulin supergene family. The sequence does not encode a typical membrane-spanning segment, but ends with 24 uncharged amino acids followed by two stop codons. This fact, together with size considerations, make it highly likely that our sequence represents NCAM-120, which lacks transmembrane or cytoplasmic domains and is attached to the membrane by phospholipid. Probes from the 5' region detect all four NCAM gene transcripts present in mouse brain consistent with the notion that the extracellular domains are common to most NCAM forms. However, a 3' probe corresponding to the hydrophobic tail and non-coding region hybridizes specifically with the smallest mRNA species. S1 nuclease protection experiments indicate that this region is encoded by exon(s) spliced out from the other mRNAs. Furthermore, our clones that are highly homologous to a published chicken NCAM sequence which codes for putative transmembrane and cytoplasmic domains elsewhere, diverge from it at the presumptive splice junction. It appears thus that alternate use of exons determines whether NCAM proteins with membrane-spanning domains are synthesized.(ABSTRACT TRUNCATED AT 250 WORDS)