Conjugation of biogenic polyamine (putrescine) with proteinase K: Spectroscopic and theoretical insights.

To understand the influence of polyamine on conformation, stabilization and function of proteins, we used multispectroscopic and simulation methods through structural, stability and kinetic measurements of proteinase K (PK) as a model enzyme combined with putrescine (Put). Structural variability of PK was investigated at different concentrations of Put, using circular dichroism, spectrofluorescence and UV-vis measurements. The secondary structure of PK was changed through β-sheet to α-helix switch induced by Put. Spontaneity of the PK-Put complexation, through hydrogen and van der Waals interactions, altered the microenvironment of aromatic residues due to the exposure of them to the solvent. UV-vis measurement also supported the secondary and tertiary structure alteration of PK as a function of Put concentration. Analysis of kinetic parameters and stability studies revealed that Put could act as an enhancer of activity and stabilizer of PK. Our experiments showed that stability and activity changes of enzyme were closely associated to the conformational alterations of enzyme. The molecular simulation results also demonstrated that Put could spontaneously bind and alter the structure of PK, thereby confirming the experimental results. Overall, the results showed that Put could bind to PK and improve its stability and activity, thereby promising various biotechnological and industrial applications.