Structure of anionic salmon trypsin in a second crystal form

Fish trypsins: potential applications in biomedicine and prospects for production

In fishes, trypsins are adapted to different environmental conditions, and the biochemical and kinetic properties of a broad variety of native isoforms have been studied. Proteolytic enzymes remain in high demand in the detergent, food, and feed industries; however, our analysis of the literature showed that, in the last decade, some fish trypsins have been studied for the synthesis of industrial peptides and for specific biomedical uses as antipathogenic agents against viruses and bacteria, which have been recently patented. In addition, innovative strategies of trypsin administration have been studied to ensure that trypsins retain their properties until they exert their action. Biomedical uses require the production of high-quality enzymes. In this context, the production of recombinant trypsins is an alternative. For this purpose, E. coli-based systems have been tested for the production of fish trypsins; however, P. pastoris-based systems also seem to show great potential in the production of fish trypsins with higher production quality. On the other hand, there is a lack of information regarding the specific structures, biochemical and kinetic properties, and characteristics of trypsins produced using heterologous systems. This review describes the potential uses of fish trypsins in biomedicine and the enzymatic and structural properties of native and recombinant fish trypsins obtained to date, outlining some prospects for their study.

Trypsin specificity as elucidated by LIE calculations, X-ray structures, and association constant measurements

The variation in inhibitor specificity for five different amine inhibitors bound to CST, BT, and the cold-adapted AST has been studied by use of association constant measurements, structural analysis of high-resolution crystal structures, and the LIE method. Experimental data show that AST binds the 1BZA and 2BEA inhibitors 0.8 and 0.5 kcal/mole more strongly than BT. However, structural interactions and orientations of the inhibitors within the S1 site have been found to be virtually identical in the three enzymes studied. For example, the four water molecules in the inhibitor-free structures of AST and BT are channeled into similar positions in the S1 site, and the nitrogen atom(s) of the inhibitors are found in two cationic binding sites denoted Position1 and Position2. The hydrophobic binding contributions for all five inhibitors, estimated by the LIE calculations, are also in the same order (-2.1 +/- 0.2 kcal/mole) for all three enzymes. Our hypothesis is therefore that the observed variation in inhibitor binding arises from different electrostatic interactions originating from residues outside the S1 site. This is well illustrated by AST, in which Asp 150 and Glu 221B, despite some distance from the S1 binding site, lower the electrostatic potential of the S1 site and thus enhance substrate binding. Because the trends in the experimentally determined binding energies were reproduced by the LIE calculations after adding the contribution from long-range interactions, we find this method very suitable for rational studies of protein-substrate interactions.

Crystal structure and nucleotide sequence of an anionic trypsin from chum salmon (Oncorhynchus keta) in comparison with Atlantic salmon (Salmo salar) and bovine trypsin

The nucleotide sequence and crystal structure of chum salmon trypsin (CST) are now reported. The cDNA isolated from the pyloric caeca of chum salmon encodes 222 amino acid residues, the same number of residues as the anionic Atlantic salmon trypsin (AST), but one residue less than bovine beta-trypsin (BT). The net charge on CST determined from the sum of all charged amino acid side-chains is -3. There are 79 sequence differences between CST and BT, but only seven sequence differences between CST and AST. Anionic CST isolated from pyloric caeca has also been purified and crystallized; the structure of the CST-benzamidine complex has been determined to 1.8A resolution. The overall tertiary structure of CST is similar to that of AST and BT, but some differences are observed among the three trypsins. The most striking difference is at the C terminus of CST, where the expected last two residues are absent. The absence of these residues likely increases the flexibility of CST by the loss of important interactions between the N and C-terminal domains. Similarly, the lack of Tyr151 in CST (when compared with BT) allows more space for Gln192 in the active site thereby increasing substrate accessibility to the binding pocket. Lys152 in CST also adopts the important role of stabilizing the loop from residue 142 to 153. These observations on CST provide a complementary view of a second cold-adapted trypsin, which in comparison with the structures of AST and BT, suggest a structural basis for differences in enzymatic activity between enzymes from cold-adapted species and mammals.