Protease-Catalyzed l-Aspartate Oligomerization: Substrate Selectivity and Computational Modeling

Molecular modification and biotechnological applications of microbial aspartic proteases

The growing preference for incorporating microbial aspartic proteases in industries is due to their high catalytic function and high degree of substrate selectivity. These properties, however, are attributable to molecular alterations in their structure and a variety of other characteristics. Molecular tools, functional genomics, and genome editing technologies coupled with other biotechnological approaches have aided in improving the potential of industrially important microbial proteases by addressing some of their major limitations, such as: low catalytic efficiency, low conversion rates, low thermostability, and less enzyme yield. However, the native folding within their full domain is dependent on a surrounding structure which challenges their functionality in substrate conversion, mainly due to their mutual interactions in the context of complex systems. Hence, manipulating their structure and controlling their expression systems could potentially produce enzymes with high selectivity and catalytic functions. The proteins produced by microbial aspartic proteases are industrially capable and far-reaching in regulating certain harmful distinctive industrial processes and the benefits of being eco-friendly. This review provides: an update on current trends and gaps in microbial protease biotechnology, exploring the relevant recombinant strategies and molecular technologies widely used in expression platforms for engineering microbial aspartic proteases, as well as their potential industrial and biotechnological applications.

Monomer Choice Influences N-Acryloyl Amino Acid Grafter Conversion via Protease Catalysis

End-capped peptides modified with reactive functional groups on the N-terminus provide a route to prepare peptide-polymer conjugates for a broad range of applications. Unfortunately, current chemical methods to construct modified peptides rely largely on solid-phase peptide synthesis (SPPS), which lacks green preparative characteristics and is costly, thus limiting its applicability to specialty applications such as regenerative medicine. This work evaluates N-terminally modified N-acryloyl-glutamic acid diethyl ester, N-acryloyl-leucine ethyl ester, and N-acryloyl-alanine ethyl ester as grafters and papain as the protease for the direct addition of amino acid ethyl ester (AA-OEt) monomers via protease-catalyzed peptide synthesis (PCPS) and the corresponding formation of N-acryloyl-functionalized oligopeptides in a one-pot aqueous reaction. It was hypothesized that by building N-acryloyl grafters from AA-OEt monomers that are known to be good substrates for papain in PCPS, the corresponding grafters would yield high grafter conversions, high ratio of grafter-oligopeptide to free NH2-oligopeptide, and high overall yield. However, this work demonstrates based on the grafter/monomers studied herein that the dominant factor in N-acryloyl-AA-OEt grafter conversion is the co-monomer used in co-oligomerizations. Computational modeling using Rosetta qualitatively recapitulates the results and provides insight into the structural and energetic bases underlying substrate selectivity. The findings herein expand our knowledge of factors that determine the efficiency of preparing N-acryloyl-terminated oligopeptides by PCPS that could provide practical routes to peptide macromers for conjugation to polymers and surfaces for a broad range of applications.

Amphiphilic mPEG-Modified Oligo-Phenylalanine Nanoparticles Chemoenzymatically Synthesized via Papain

Amphiphilic mPEG-modified peptide nanoparticles were developed from oligo-phenylalanine (OPhe) nanoparticles (NPs) synthesized via papain. Tyndall effects indicate that OPhe NPs are amphiphobic. Addition of protein perturbants, sodium dodecyl sulfate (SDS), and urea, in the dispersion solution of OPhe NPs can significantly reduce the R _h,m value of NPs, from approximately 749.2 nm to about 200 nm. Therefore, the hydrophobic interaction and hydrogen bonding play major roles in maintaining the aggregation of OPhe NPs. Using the "grafting to" method, the methoxypolyethylene-modified OPhe NPs (mPEG-g-OPhe NPs) were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), ¹H NMR, electrospray ionization mass spectrometry (ESI-MS), and dynamic light scattering (DLS). The attenuated total reflectance (ATR) spectrum of OPhe NPs and mPEG-g-OPhe NPs demonstrate that the secondary structures of these NPs are mainly β-type. mPEG-g-OPhe NPs can self-aggregate into spherical micelles both in water and cyclohexane. Increasing the chain length of the mPEG moiety, the critical micellar concentrations of mPEG-g-OPhe NPs increased in water but decreased in cyclohexane. The light stability, thermal stability, hydrolysis stability, and encapsulation stability of curcumin were significantly promoted by encapsulation in the micelles formed by mPEG-g-OPhe NPs. The protective effects regularly varied with the variations in the mPEG chain length of mPEG-g-OPhe NPs.