Sequence of three cDNAs encoding an alkaline midgut trypsin from Manduca sexta

Trypsin isolated from the midgut of the tobacco hornworm, Manduca sexta, is inhibited by synthetic pro-peptides in vitro

The seven residue synthetic peptides VPAYPQR and VPANPQR, identical to the pro-regions of midgut trypsins from Manduca sexta, inhibit the peptidase activity of the mature enzymes. The inhibitory potencies of these peptides towards purified insect trypsin were determined and were found to be more potent at pH 7.0 than at pH 10.0. These peptides did not inhibit porcine trypsin, nor were they degraded rapidly by purified insect trypsin. We suggest that these particular peptides, and insect proregions in general, may be suitable for use in genetically engineered plants as insect specific inhibitors of digestive proteases.

An immunocytochemical investigation of trypsin secretion in the midgut of the stablefly, Stomoxys calcitrans

Musca domestica trypsin antibody cross-reacts with polypeptide bands of M(r) 25,000 and 30,000 showing proteolytic activity from Stomoxys calcitrans midgut extracts. Secretory granules from the main enzyme-secreting region, the opaque zone, stained heavily with the trypsin antibody in both unfed and blood-fed flies. Heterogeneous staining of granules suggests the unequal distribution of trypsin in secretory granules. This is also consistent with the occurrence of non-parallel secretion, which is also suggested by the possible preferential release of smaller, heavily stained secretory granules in fed flies. The predigestive, anterior midgut region responsible for rapid dehydration of the blood meal, the reservoir zone, contains a different population of secretory granules which stain heavily with trypsin antibody. This zone contains 20% of the midgut trypsin activity in unfed flies; trypsins are held here as proenzymes which are probably only activated postsecretion. In the midgut lumen of both unfed and blood-fed flies, trypsin is mainly immunolocalized in the ectoperitrophic space. Enzyme assays suggest that 5-15% of the lumenal trypsin is associated with the peritrophic matrix. The finding of intact secretory granules plus cell debris in the ectoperitrophic space of opaque and lipoid zones of blood-fed flies supports the contention that some trypsin is released by apocrine secretion in this insect.

Mitochondrial cytochrome C oxidase subunit I of Manduca sexta and a comparison with other invertebrate genes

A cDNA encoding mitochondrial cytochrome c oxidase subunit I (mt COI) from Manduca sexta (Lepidoptera: Sphingidae) was cloned and sequenced. AT (adenine-thymine) content is high and codon usage is biased and likely reflects the role of mt COI in electron transport. The encoded protein is 514 amino acids long, contains seven invariant His residues observed in COIs in all organisms and would be predicted to be composed of 12 transmembrane regions.

Molecular sequencing and modeling of Neobellieria bullata trypsin. Evidence for translational control by Neobellieria trypsin-modulating oostatic factor

Trypsin mRNA from the grey fleshfly (Neobellieria bullata) was reversed transcribed and amplified by means of PCR. Two cDNA species of 600 bp and 800 bp were cloned and sequenced. The 3' end of the gene (300 bp) was amplified by means of the rapid-amplification-of-cDNA-ends method, cloned and sequenced. The deduced protein sequence of 254 amino acids exhibited 46% identity to Drosophila trypsin and 32% identity to Anophiline trypsin and Aedes trypsin. Three-dimensional models of Neobellieria trypsin and Drosophilia trypsin were built and compared. Both models contain two domains of beta-barrel sheets as was shown by means of X-ray crystallography of mammalian trypsin. The catalytic active site is composed of the canonical triad of His42, Asp87 and Ser182 whereas Asp176 sits as the bottom of the specificity pocket. Southern blot analysis suggested that Neobellieria trypsin is encoded by one gene. Northern blot analysis showed that an early trypsin transcript is found in the midgut of sugar-fed females. This message disappeared after a liver meal, and was replaced by a late transcript. Injection of trypsin-modulating oostatic factor (TMOF) at 10(-9) M prevented the disappearance and the translation of the early transcript. TMOF did not prevent the appearance of the late transcript. However, in the presence of the hormone the late transcript was not translated. Thus, TMOF is the biological signal that terminates the translation of trypsin mRNA in the fleshfly gut and probably in the mosquito gut.

Early trypsin, a female-specific midgut protease in Aedes aegypti: isolation, aminoterminal sequence determination, and cloning and sequencing of the gene

Early trypsin is a female-specific protease present in the Aedes aegypti midgut during the first hours after ingestion of a blood meal. It plays an essential role in the transcriptional activation of the late trypsin form, the major midgut endoprotease involved in the blood meal digestion. Early trypsin is the most abundant midgut polypeptide isolated by benzamidine-sepharose affinity chromatography 3 h after feeding. The amino-terminal sequence of the early trypsin protein matches that of the 3a1 cDNA for a putative trypsinogen described by Kalhok et al. (Insect. Molec. Biol., 2, 71-79, 1993). The early trypsin cDNA was over expressed in Escherichia coli. Polyclonal antibodies generated against this recombinant protein were used to show that the enzyme was present in the midgut during the first 4 h after feeding. A 2.5 kb genomic clone of the early trypsin was isolated, mapped and subcloned. A 1.56 kb subclone, corresponding to 1303 bp of the upstream regulatory region and 265 bp of the coding region, was sequenced. The gene contains a 64 nucleotide intron which interrupts the codon for Val at position 18 of the protein. This Val is located toward the end of the putative signal sequence of the protein.

Genomic organization and expression of a trypsin gene from the spruce budworm, Choristoneura fumiferana

A 7 kb (kilobase) genomic fragment containing a trypsin gene from the spruce budworm Choristoneura fumiferana was isolated and sequenced. The coding sequence is interrupted by two introns; these occur at the same positions as the first two introns of mammalian trypsin genes. The three exons encode 256 amino acids. The deduced protein sequence displays all of the structural features that characterize trypsin enzymes in other eukaryotic organisms. Genomic Southern hybridization showed that there is only one copy of the trypsin gene in the Choristoneura genome. This gene is expressed in the insect midgut, where the pH is extremely high. The complete lack of Lysine residues may be an adaptation to the high pH conditions. Extensive sequencing of the flanking regions did not reveal the presence of any linked trypsin-encoding genes. Instead, several short repetitive sequences and a sequence homologous to a Drosophila reverse transcriptase gene was identified in this genomic region.

Purification, characterization and cDNA sequence of an alkaline chymotrypsin from the midgut of Manduca sexta

The chymotrypsin in the midgut of Manduca sexta has been purified, characterized and the cDNA encoding the protein has been cloned. The enzyme exists as a monomer of approx. 24 kDa and shows maximal activity between pH 10.5 and 11.0. Kinetic studies reveal that the Michaelis constant (Km) for the synthetic substrate N-succinyl-Ala-Ala-Pro-Phe p-nitroanilide varies only slightly between pH 7.5 and 11.5 and the Dixon plot shows a kinetically significant pKa at 9.2. The specificity of the purified enzyme was determined to be the peptide bond on the carboxyl side of tyrosine, phenylalanine, tryptophan, histidine, leucine, threonine and glycine. The protease is inhibited by TPCK, PMSF, chymostatin and DFP. A 1 kilobase chymotrypsin cDNA clone was isolated and sequenced. The cDNA sequence encodes a preproenzyme with a putative 17 amino acid signal sequence, a 41 amino acid activation peptide and a mature enzyme of 235 amino acids. The isolated clone encodes the highly conserved active site residues (His, Asp, Ser) and specificity pocket residues present in bovine chymotrypsinogen B. Northern analysis localizes the mRNA for the chymotrypsin to the anterior and middle third of the midgut.