LUTI: a double-function inhibitor isolated from naked flax seeds

Acute glucose fluctuation during the postprandial period causes a risk for type 2 diabetes mellitus (T2DM). α-Glucosidase inhibitors have been approved as therapeutic agents for diabetes. In the present study, a protein with α-glucosidase inhibitory activity from Flax (Linum usitatissimum) seeds was isolated using a one-step purification with Q-Sepharose4B column, followed by Sephacryl S-200 size-exclusion chromatography. It was identified as a trypsin inhibitor, named L. usitatissimum trypsin inhibitor (LUTI). The half maximal inhibitory concentration (IC50) of LUTI was 113.92 μM for α-glucosidase and 6.17 μM for trypsin. Lineweaver-Burk kinetic experiment showed that the protein exhibited two distinct inhibitory modes, a competitive inhibitor type for α-glucosidase and a non-competitive type for trypsin. The interaction between LUTI and α-glucosidase was detected through gel filtration chromatography and dynamic light scattering. Increased glucose consumption and lactic acid production were also observed following LUTI treatment in Caco-2 and HepG2 cells. LUTI inhibits not only the activity of trypsin but also the activity of α-glucosidase. It is expected that LUTI will become an oral hypoglycemic polypeptide drug for T2DM.

Growth Impairment Caused by Raw Linseed Consumption: Can Trypsin Inhibitors Be Harmful for Health?

Linseed (Linun usitatissimum L.) is an important oilseed whose nutritional value can be impaired due to presence of antinutritional factors and low protein digestibility. Protein fractions from raw linseed meal were extracted, isolated and analyzed in vitro and in vivo. Globulins, the major protein fraction of linseed, showed low in vitro susceptibility to trypsin and chymotrypsin, but its in vivo digestibility was 93.2 %. Albumin fraction had high trypsin inhibition activity (5250 Inhibition Units g(-1)) and presented low molecular mass protein bands, similar to known trypsin inhibitors. Raw linseed consumption caused negative effects on rat growth and reduction of intestinal villi. Results indicate that raw linseed meal must not be used as an exclusive source of protein regardless of the major proteins have high digestibility; digestive enzymes inhibitors in raw linseed probably reduces the protein utilization.

Pancreatic proteolytic enzymes of ostrich purified on immobilized protein inhibitors. Characterization of a new form of chymotrypsin (Chtr1)

Four forms of chymotrypsin (Chtr1, Chtr2, Chtr3, Chtr4), one form of trypsin and one form of elastase were purified from a slightly alkaline extract of ostrich (Struthio camelus) pancreas. The zymogens in the crude extract were activated with immobilized trypsin and then separated by affinity chromatography using immobilized inhibitors and ion exchange chromatography. One of the purified forms of chymotrypsin (Chtr1) exhibited an unusual interaction with the highly selective protein trypsin inhibitor from Cucurbita maxima (CMTI). Interactions with other protein trypsin inhibitors such as basic pancreatic trypsin inhibitor (BPTI), soybean trypsin inhibitor (STI), trypsin inhibitors from Cyclanthera pedata (CyPTI), Cucurbita pepo (CPTI), Cucurbita pepo var. giramontia (CPGTI) and Linum usitatissimum (LUTI) were also investigated. This study demonstrated the affinity of Chtr1 to inhibitors containing Arg at P1 position. Studies of substrate specificity of Chtr1 using oxidized B-chain of insulin revealed four susceptible bonds: Tyr15-Leu16, Phe24-Phe25, Phe25-Tyr26 and, surprisingly, Arg22-Gly23. The amino acid composition, as well as the first 13 residues of the N-terminal amino acid sequence, was determined. Studies of ostrich elastase showed that it can interact with immobilized CMTI in the presence of 5 M NaCl. This unusual characteristic is reported for the first time and suggests that elastase specificity depends on ionic strength. The kinetic constants K(M), k(cat) and k(cat)/K(M) for purified ostrich trypsin, chymotrypsin 4 and elastase were also determined.

Analysis of biological and synthetic ribonucleic acids by liquid chromatography-mass spectrometry using monolithic capillary columns

Ion-pair reversed-phase high-performance liquid chromatography (IP-RP-HPLC) has been evaluated as a method for the fractionation and desalting of ribonucleic acids prior to their characterization by electrospray ionization mass spectrometry. Monolithic, poly(styrene-divinylbenzene)-based capillary columns allowed the rapid and highly efficient fractionation of both synthetic and biological ribonucleic acids. The common problem of gas-phase cation adduction that is particularly prevalent in the mass spectrometric analysis of ribonucleic acids was tackled through a combination of chromatographic purification and the addition of ethylenediaminetetraacetic acid to the sample at a concentration of 25 mmol/L shortly before on-line analysis. For RNA molecules ranging in size from 10 to 120 nucleotides, the mass accuracies were typically better than 0.02%, which allowed the characterization and identification of failure sequences and byproducts with high confidence. Following injection of a 500 nL sample onto a 60 x 0.2 mm column, the limit of detection for a 120-nucleotide ribosomal RNA transcript from Escherichia coli was in the 50-80 fmol range. The method was applied to the analysis of synthetic oligoribonucleotides, transfer RNAs, and ribosomal RNA. Finally, sequence information was derived for low picomole amounts of a 32-mer RNA upon chromatographic purification and tandem mass spectrometric investigation in an ion trap mass spectrometer. Complete series of fragment ions of the c- and y-types could be assigned in the tandem mass spectrum. In conclusion, IP-RP-HPLC using monolithic capillary columns represents a very useful tool for the structural investigation and quantitative determination of RNAs of synthetic and biological origin.

LTCI, a novel chymotrypsin inhibitor of the potato I family from the earthworm Lumbricus terrestris. Purification, cDNA cloning, and expression

A novel chymotrypsin inhibitor of the potato I protease inhibitor family from the earthworm Lumbricus terrestris was purified. The inhibitor, named LTCI, was isolated by methanol extraction, affinity chromatography on immobilized methylchymotrypsin, and ion exchange chromatography followed by RP-HPLC. The 7076 Da inhibitor consists of a single polypeptide chain of 64-amino-acid residues without disulfide bridges. LTCI is the first of the potato I protease inhibitors with Tyr in position P1 of the reactive site. cDNA analysis revealed that LTCI is produced as a 86-amino-acid precursor with a 22-amino-acid secretory signal peptide. RT-PCR analysis demonstrates that LTCI mRNA is expressed in body wall, intestine, and coelomocytes. The recombinant LTCI was produced in Escherichia coli as a fusion protein with intein and chitin binding domain using IMPACT-CN system.

Primary structure and reactive site of a novel wheat proteinase inhibitor of subtilisin and chymotrypsin

The proteinase inhibitor WSCI, active in inhibiting bacterial subtilisin and a number of animal chymotrypsins, was purified from endosperm of exaploid wheat (Triticum aestivum, c.v. San Pastore) by ion exchange chromatography and its complete amino acid sequence was established by automated Edman degradation. WSCI consists of a single polypeptide chain of 72 amino acid residues, has a molecular mass of 8126.3 Da and a pl of 5.8. The inhibition constants (Ki) for Bacillus licheniformis subtilisin and bovine pancreatic alpha-chymotrypsin are 3.92 x 10(-9) M and 7.24 x 10(-9) M, respectively. The inhibitor contains one methionine and of tryptophan residue and has a high content of essential amino acids (41 over a total of 72 residues), but no cysteines. The primary structure of WSCI shows high similarity with barley subtilisin-chymotrypsin isoinhibitors of the Cl-2 type and with maize subtilisinchymotrypsin inhibitor MPI. Significant degrees of similarity were also found between sequences of WSCI and of other members of the potato inhibitor I family of the serine proteinase inhibitors. The wheat inhibitor WSCI has a single reactive site (the peptide bond between methionyl-48 and glutamyl-49 residues) as identified by affinity chromatography and sequence analysis.

Arginine-specific cysteine proteinase from porphyromonas gingivalis as a convenient tool in protein chemistry

RgpB, a cysteine proteinase produced by Porphyromonas gingivalis, exhibits proteolytic activity selectively directed against peptide bonds containing an arginine residue in the P1 position. Here we show that this enzyme can be used for very efficient and specific protein cleavage. RgpB is highly active even at high concentrations of denaturing agents, including urea (up to 6 M) and SDS (0.1%), both of them being commonly used for solubilization of insoluble proteins and peptides. Moreover, RgpB is able to digest polypeptide chains in buffers supplemented with 1% Triton X-100, 1% octyl or decylpyranoside, detergents employed for the enzymatic digestion of proteins transferred onto nitrocellulose membranes. These features render RgpB a suitable tool for use in protein chemistry.