Altai maral (Cervus elaphus sibiricus) chymosin structural characterization and modeling the enzyme interaction with...

Chymosins (Chn's) are not only popular industrial milk coagulants, but also attractive models for studying the mechanisms of target peptide bonds recognition by aspartate peptidases. Despite the high amino acid sequence homology and similarity of their tertiary structures, Chns of various mammals may have significantly different enzymatic properties. We have obtained Altai maral (Cervus elaphus sibiricus) crystal structure. Bovine and dromedary camel chymosins with known structures and characterized specificities were used for comparative analysis. The recombinant maral Chn (rChn-Cer) specificity was determined by chromatograph mass spectrometry after enzyme incubation with peptide substrates repeating the maral, bovine and camel κ-caseines (κ-CN's) chymosine sensitive regions. Analysis of resulting products indicates that in the maral and bovine κ-CN sequences, maral rChn hydrolyzes the F105-M106 bond, but in the camel substrate, it hydrolyzes the F97-I98 bond. According to the comparative analysis of spatial structures, the arrangement of catalytic amino acid residues of maral, bovine and camel Chn's is almost identical. The obtained rChn-cer structure were used as a starting model for protein-protein docking and molecular dynamics to describe the interactions of the enzyme catalytic center with synthetic peptide substrates repeating the chymosine sensitive regions of maral, bovine and camel κ-CN. The obtained results could be useful for understanding the mechanisms of interaction of chymosins with substrates of different species.