Isolation of milk-clotting enzyme from transgenic sheep milk and its comparison with calf chymosin

Recombinant expression and characterization of Oryctolagus cuniculus chymosin in Komagataella phaffii (Pichia pastoris)

This study was conducted for investigating expression and enzymatic characteristics of recombinant Oryctolagus cuniculus chymosin (ROCC) expressed in Pichia pastoris. SDS-PAGE of partially purified supernatant displayed two distinct molecular bands approximately at the sizes of 40 kDa and 45 kDa corresponding to chymosin and partially glycosylated chymosin, respectively. Proteolysis assay demonstrated that rabbit chymosin was more specific compared to bovine and camel chymosins when it comes to hydrolyzing α, β, and κ-casein. Rabbit chymosin kept its stability in a wide pH range (3.0-6.0) at 37 °C for 8 h. Active chymosin exhibited maximum enzymatic activity at 40 °C and pH 4.0 with the addition of 75 mM CaCl₂. The ROCC clotting activity on donkey, cow, goat, lamb, camel milk was determined as 40, 10, 5.7, 3.07, and 2.66 IMCU/mL, respectively. These results revealed that ROCC might possess a potential for incorporation into cheese manufacture technology as a milk-clotting enzyme.

Easily Accessible Protein Nanostructures via Enzyme Mediated Addressing

Site-specific formation of nanoscaled protein structures is a challenging task. Most known structuring methods are either complex and hardly upscalable or do not apply to biological matter at all. The presented combination of enzyme mediated autodeposition and nanosphere lithography provides an easy-to-apply approach for the buildup of protein nanostructures over a large scale. The key factor is the tethering of enzyme to the support in designated areas. Those areas are provided via prepatterning of enzymatically active antidots with variable diameters. Enzymatically triggered protein addressing occurs exclusively at the intended areas and continues until the entire active area is coated. After this, the reaction self-terminates. The major advantage of the presented method lies in its easy applicability and upscalability. Large-area structuring of entire support surfaces with features on the nanometer scale is performed efficiently and without the necessity of harsh conditions. These are valuable premises for large-scale applications with potentials in biosensor technology, nanoelectronics, and life sciences.

Codon Optimization of the "Bos Taurus Chymosin" Gene for the Production of Recombinant Chymosin in Pichia pastoris

Codon optimization of the Bos taurus Chymosin gene (CYM) for its expression in Pichia pastoris was performed in this study. A synthetic CYM gene was designed in silico by replacing codons rarely used by P. pastoris with equivalent nucleotide combinations that codify for the same amino acid but that are more frequently encountered in the genome of P. pastoris. A total of 332 nucleotides were modified to optimize 289 codons. The synthetic CYM gene was cloned into the expression vector pPICZαA and transformed into P. pastoris. The transformed strains were grown in artificial media supplemented with glycerol as a carbon source to increase biomass and then cultured in a similar medium replacing glycerol with methanol as a carbon source to initiate gene induction. Raw extracts of the growth media exhibited milk-clotting activity of 146.11 SU/mL. Produced recombinant chymosin showed coagulant activity from 25 to 50 °C, and within a pH range of 5-6.9, having optimum activity at 35-40 °C, and pH 5.0. These results show that codon optimization is a viable strategy to improve CYM gene expression levels in P. pastoris for the production of recombinant chymosin.

PsoP1, a milk-clotting aspartic peptidase from the basidiomycete fungus Piptoporus soloniensis

The first enzyme of the basidiomycete Piptoporus soloniensis, a peptidase (PsoP1), was characterized after isolation from submerged cultures, purification by fractional precipitation, and preparative native-polyarylamide gel electrophoresis (PAGE). The native molecular mass of PsoP1 was 38 kDa with an isoelectric point of 3.9. Similar to chymosin from milk calves, PsoP1 showed a maximum milk-clotting activity (MCA) at 35-40 °C and was most stable at pH 6 and below 40 °C. The complete inhibition by pepstatin A identified this enzyme as an aspartic peptidase. Electrospray ionization-tandem MS showed an amino acid partial sequence that was more homologous to mammalian milk clotting peptidases than to the chymosin substitute from a fungal species, such as the Zygomycete Mucor miehei. According to sodium dodecyl sulfate-PAGE patterns, the peptidase cleaved κ-casein in a way similar to chymosin and hydrolyzed β-casein slowly, as it would be expected from an efficient chymosin substitute.

Purification and characterization of milk clotting enzyme from goat (Capra hircus)

Chymosin, the major component of rennet (milk clotting enzyme), is an acid protease produced in the fourth stomach of milk-fed ruminants including goat and sheep in the form of an inactive precursor prochymosin. It is responsible for hydrolysis of kappa-casein chain in casein micelles of milk and therefore, used as milk coagulant in cheese preparation. The present investigation was undertaken to purify and characterize goat (Capra hircus) chymosin for its suitability as milk coagulant. The enzyme was extracted from abomasal tissue of kid and purified nearly 30-fold using anion exchanger and gel filtration chromatography. Goat chymosin resolved into three major active peaks, indicating possible heterogeneity when passed through DEAE-cellulose ion exchange column. The purified enzyme had a molecular mass of 36 kDa on SDS-PAGE, which was further confirmed by Western blot analysis. The purified enzyme preparation was stable up to 55 degrees C with maximum activity at 30 degrees C. The milk clotting activity was decreased steadily as pH is increased and indicated maximum activity at pH 5.5. Proteolytic activity of goat chymosin increased with incubation time at 37 degrees C. Goat chymosin was found to be more thermostable than cattle chymosin and equally stable to buffalo chymosin.

A comparative study of functional properties of calf chymosin and its recombinant forms

The action of calf chymosin obtained from transgenic sheep milk and the recombinant protein expressed in yeast Kluyveromyces lactis (Maxiren) on fluorogenic peptide substrates, namely Abz-A-A-F-F-A-A-Ded, Abz-A-A-F-F-A-A-pNA, Abz-A-F-F-A-A-Ded, Abz-A-A-F-F-A-Ded, Abz-A-A-F-F-Ded, Abz-A-A-F-F-pNA, and heptapeptide L-S-F-M-A-I-P-NH2, a fragment of kappa-casein (the native chymosin substrate), was investigated. It has been established that transgenic chymosin and recombinant chymosin (Maxiren) differ from the native enzyme in their action on low molecular weight substrates, whereas there was no difference in enzymatic action on protein substrates. Pepstatin, a specific inhibitor of aspartic proteinases, inhibits the recombinant chymosin forms less efficiently than the native enzyme. Perhaps this is associated with local conformational changes in the substrate binding site of recombinant chymosin occurring during the formation of the protein globule.