Enzymatic methods for cleaving proteins

Succinylation of zein and gelatin hydrolysates improved their ice recrystallization inhibition activity

The goal of this research was to enhance the ice recrystallization inhibition (IRI) activity of zein and gelatin hydrolysates (ZH and GH, respectively) by succinylation modification. ZH was prepared by Alcalase treatment for 3 h and then modified by succinic anhydride (SA); whereas GH was made by Alcalase hydrolysis for 0.25 h and succinylated by n-octylsuccinic anhydride (OSA). After 0.5 h of annealing at -8 °C at 40 mg/mL, modified hydrolysates decreased the average Feret's diameter of ice crystal from 50.2 μm (polyethylene glycol, negative control) to 28.8 μm (SA modified ZH) and 29.5 μm (OSA modified GH) in comparison to the unmodified hydrolysates, which had the crystal size of 47.2 μm (ZH) and 45.4 μm (GH). Also, the two succinylated samples had altered surface hydrophobicity, which potentially contributed to their enhanced IRI activity. Our results indicate that succinylation of food-derived protein hydrolysates can improve their IRI activity.

Digestion of the lambda cI repressor with various serine proteases and correlation with its three dimensional structure

Partial proteolysis of the lambda cI repressor has been carried out systematically with trypsin, chymotrypsin, elastase, endoproteinase Glu-C, kallikrein, and thrombin. The cleavage sites have been determined by (i) comparison of fragments produced and observed in SDS-polyacrylamide gel with known fragments and plots of distance migrated versus log (molecular weight of fragment), (ii) partial Edman sequencing of the stable C-terminal fragments to identify cleavage points, and (iii) electrospray mass spectrometry of fragments produced. Most cleavage points are found to occur in the region 86-137, saving some in the N-terminal domain observed for trypsin and Glu-C. Region 86-137 can be further subdivided into three regions 86-91, 114-121, and 128-137 prone to cleavage, with intermediate regions resistant to cleavage to all six proteases. These resistant regions show that much of the region 93-131 previously called a 'linker' is actually part of the C-domain as first proposed in all models from our laboratory. Region 92-114 includes the cleavage site Ala-Gly, which must be buried in the intact repressor. The observed cleavage points in region 114-137 can be used to judge the best among three previously proposed models since they differ from each other in the structure of region 93-131. Model 1j5g is adjudged to be better than model 1lwq (which is based on 1kca, a crystal structure) as susceptible residues are more exposed in the former and lack of cleavages at six sites is better explained. Likewise, the models 1j5g and 1lwq are compared with a recent crystal structure of fragment 101-229 in 2ho0 and another low resolution crystal structure in 3bdn.

Delivering multiple anticancer peptides as a single prodrug using lysyl-lysine as a facile linker

A large 40-residue precursor peptide (propeptide 5) was synthesized by linking together four designed anticancer peptide analogs to the neuropeptides: vasoactive intestinal peptide, somatostatin, bombesin and substance P, using enzyme cleavable lysyl-lysine linkers. On incubation with the enzyme trypsin, propeptide 5 was cleaved in a sequence-specific manner at the lysyl-lysine residues in the linker to release the individual peptide fragments which were identified by LC-MS. Another precursor peptide (propeptide 5a), consisting of two of the peptide analogs linked through lysyl-lysine linker, was also preferentially cleaved at the Lys-Lys site on incubation with the enzyme trypsin. Propeptide 5 showed potent anticancer activity, both in vitro and in vivo, which was greater than that of the individual component peptides. The enhanced activity suggests that the propeptide is possibly cleaved in the biological system at the lysyl-lysine site to yield the individual peptide analogs, which together show a synergistic effect. On the basis of these experimental findings, it can be concluded that pairs of basic amino acids such as Lys-Lys can be used as facile linkers for delivering multiple biologically active peptides.