Isolation and characterization of carboxypeptidase III from germinating triticale grains

Isolation and detection of a KDEL-tagged recombinant cholera toxin B subunit from Nicotiana benthamiana

Here we describe refined methods for the isolation and detection of a KDEL-tagged, plant-produced recombinant cholera toxin B subunit (CTB) that exhibits unique mucosal wound healing activity. The protein was transiently overexpressed in Nicotiana benthamiana, which generates some C-terminal KDEL truncated molecular species that are deficient in epithelial repair activity. With a new CHT chromatographical method described herein, these product-derived impurities were successfully separated from CTB with the intact KDEL sequence, as confirmed by mass spectrometry. In addition, an immunoassay capable of specifically detecting GM1 ganglioside-binding CTB with intact KDEL sequences was developed. Coupled together, these methods will aid in the quality control of KDEL-attached CTB produced in plant-based manufacturing systems towards a novel topical biotherapeutic for the treatment of acute and chronic mucosal inflammation.

Insights on the Proteases Involved in Barley and Wheat Grain Germination

Seed storage proteins must be hydrolyzed by proteases to deliver the amino acids essential for embryo growth and development. Several groups of proteases involved in this process have been identified in both the monocot and the dicot species. This review focuses on the implication of proteases during germination in two cereal species, barley and wheat, where proteolytic control during the germination process has considerable economic importance. Formerly, the participation of proteases during grain germination was inferred from reports of proteolytic activities, the expression of individual genes, or the presence of individual proteins and showed a prominent role for papain-like and legumain-like cysteine proteases and for serine carboxypeptidases. Nowadays, the development of new technologies and the release of the genomic sequences of wheat and barley have permitted the application of genome-scale approaches, such as those used in functional genomics and proteomics. Using these approaches, the repertoire of proteases known to be involved in germination has increased and includes members of distinct protease families. The development of novel techniques based on shotgun proteomics, activity-based protein profiling, and comparative and structural genomics will help to achieve a general view of the proteolytic process during germination.

The protein composition of the digestive fluid from the venus flytrap sheds light on prey digestion mechanisms

The Venus flytrap (Dionaea muscipula) is one of the most well-known carnivorous plants because of its unique ability to capture small animals, usually insects or spiders, through a unique snap-trapping mechanism. The animals are subsequently killed and digested so that the plants can assimilate nutrients, as they grow in mineral-deficient soils. We deep sequenced the cDNA from Dionaea traps to obtain transcript libraries, which were used in the mass spectrometry-based identification of the proteins secreted during digestion. The identified proteins consisted of peroxidases, nucleases, phosphatases, phospholipases, a glucanase, chitinases, and proteolytic enzymes, including four cysteine proteases, two aspartic proteases, and a serine carboxypeptidase. The majority of the most abundant proteins were categorized as pathogenesis-related proteins, suggesting that the plant's digestive system evolved from defense-related processes. This in-depth characterization of a highly specialized secreted fluid from a carnivorous plant provides new information about the plant's prey digestion mechanism and the evolutionary processes driving its defense pathways and nutrient acquisition.

Carboxypeptidase I from triticale grains and the hydrolysis of salt-soluble fractions of storage proteins

Carboxypeptidase I was purified from triticale grains (×Triticosecale Wittm.) by a 5-step purification procedure including gel filtration, cation-exchange chromatography and affinity chromatography. The enzyme was purified 595.9 fold with a 1.58% recovery. Triticale carboxypeptidase I is a homodimer with a molecular weight of 124.2 kDa and a subunit weight of 55.2 kDa. Each subunit is composed of two polypeptide chains (33.4 and 21.3 kDa). Serine was found in the active site of triticale carboxypeptidase I; DFP (diisopropylflourophosphate) and other applied inhibitors of serine proteases inhibited the enzyme activity. Triticale carboxypeptidase I hydrolyzes N-CBZ-dipeptide (N-carbobenzoxy-dipeptide) substrates at low pH. N-CBZ-Phe-Ala, N-CBZ-Phe-Leu and N-CBZ-Ala-Met were hydrolyzed with the highest rates. The lowest K(m) value and the highest k(cat)/K(m) ratio were observed for hydrolysis of N-CBZ-Phe-Ala. Studies on the amino acid sequence revealed that the purified enzyme is homologous to carboxypeptidase I from barley. Analyses of conserved regions in the sequence of triticale carboxypeptidase I revealed the presence of Ser, Asp and His that compose the catalytic triad. Intact storage proteins were poor substrates for carboxypeptidases. Carboxypeptidase I together with carboxypeptidase III effectively degraded albumins proteolytically modified by endopeptidase EP8. Modified globulins were degraded at a slower rate, and all three carboxypeptidases were required for a significantly increased activity. Studies of the expression of the carboxypeptidase I gene revealed that the synthesis of the enzyme occurs mainly in the scutellum of the grain. The enzyme is also expressed in the aleurone layer of the grains, although its function in this tissue is unknown.