In silico study on the effect of surface lysines and arginines on the electrostatic interactions and protein stability

Random mutagenesis and semi-rational design enhance the tolerance of Metabacillus litoralis C44 α-L-rhamnosidase

Isoquercitrin is a flavonoid with wide range of physiological activities, which has significant applications in the pharmaceutical and nutraceutical industries, but faces challenges in industrial production due to its low yields and high production cost. Based on a comparison of homologous protein sequences, D222 and E486 were identified as active sites of the α-L-rhamnosidase MlRha4 derived from Metabacillus litoralis C44. Random mutagenesis of the α-L-rhamnosidase MlRha4 gene sequence from strain C44 was performed using error-prone PCR, and reverse mutation was performed on the inactive mutants, followed by semi-rational design, resulting in 11 positive mutants. Subsequent combinatorial mutagenesis yielded mutant R-28 (K89R-K70R-E475D) with a 70.6 % increase in enzyme activity. Compared with the wild-type MlRha4, the optimal reaction temperature of R-28 was increased by 5 °C, the optimal pH was increased from 7.5 to 8.0, the conversion rate of 10 g/L rutin for 24 h reached 100 %, and the maximum substrate concentration for the mutant enzyme R-28 was up to 300 g/L rutin. Molecular dynamics simulation of R-28 and MlRha4 revealed a more stable structure of R-28. The free energy analysis shows that R-28 has a higher affinity for rutin, which is consistent with the change of Km value. This work identified an α-L-rhamnosidase that operates effectively in weakly alkaline environments. Through random mutagenesis and semi-rational design, enzyme activity and tolerance were significantly improved, offering a reference for the industrial-scale production of isoquercetin from rutin.

Structural and Energetic Insights into the Binding of L- and D-Arginine Analogs with Neuropilin-1 (NRP1): Molecular Docking, Molecular Dynamics and DFT Calculations

Neuropilin-1 (NRP1) is a transmembrane glycoprotein that binds numerous ligands, including vascular endothelial growth factor A (VEGFA) that stimulates blood vessel formation. Preclinical trials propose that NRP1 inhibition blocks neoplasm cell proliferation and slows tumor growth by suppressing angiogenesis. As such, VEGFA/NRP1 signaling is a potential target for carcinoma inhibition. Since arginine (Arg) regulates nutrient-responsive rapamycin signaling, which in turn regulates cell growth and metabolism, Arg, as well as simple structural variations of L- and D-Arg, were selected to study in-silico structural and energetic influences of such ligands on NRP1 signaling. Initially, AutoDock Vina1.1.2 software performance was assessed to predict binding modes of Arg analogs with NRP1 based on the available experimental data. Molecular docking and molecular dynamics (MD) simulations over 100 ns were run to inspect the potency of Arg analogs to bind with NRP1. Analog-NRP1 complex binding affinities (ΔGbinding) were evaluated using the MM/GBSA approach. Results indicated that L-/D-Agd- and L-/D-Agn-NRP1 complexes exhibited binding affinities greater than the co-crystallized L-homoarginine ligand (calc.-31.2 kcal.mol-1) with ΔGbinding values of -40.5/-40.6 and -40.0/-36.2 kcal.mol-1, respectively. Structural and energetic analyses were performed to examine further L-/D-Agd and L-/D-Agn. Quantum mechanical calculations were performed to confirm the outcomes obtained from docking computations and MD simulations.

Proteome-Wide Deconvolution of Drug Targets and Binding Sites by Lysine Reactivity Profiling

Recently, numerous efforts have been devoted to identifying drug targets and binding sites in complex proteomes, which is of great importance in modern drug discovery. In this study, we developed a robust lysine reactivity profiling method to systematically study drug-binding targets and binding sites at the proteome level. This method is based on the principle that binding of a drug to a specific region of target proteins will change the reactivity of lysine residues that are located at this region, and these changes can be detected with an enrichable and lysine reactive probe. Coupled with data-independent acquisition (DIA), the known target proteins and corresponding binding sites were successfully revealed from K562 cell lysates for three model drugs: geldanamycin, staurosporine, and dasatinib. In addition, the drug-induced conformational changes of certain targets were also revealed by our method during the screening of staurosporine. The screening sensitivity of our method revealed from the screening of stuarosporine and dasatinib was comparable with that of thermal proteome profiling (TPP) or machine learning-based limited proteolysis (LiP-Quant). Overall, 21 and 4 kinase targets, including adenosine 5'-triphosphate (ATP)-binding targets, were identified for staurosporine and dasatinib in K562 cell lysates, respectively. We found that target proteins identified by TPP, LiP-Quant, and our method were complementary, emphasizing that the development of new methods that probe different properties of proteins is of great importance in drug target deconvolution. We also envision further applications of our method in proteome-wide probing multiple events that involve lysine reactivity changes.

Prediction of ligand modulation patterns on membrane receptors via lysine reactivity profiling

A mass spectrometry-based lysine reactivity profiling strategy for the prediction of the ligand modulation patterns on neuronal membrane receptors.

Lysines and Arginines play non-redundant roles in mediating chemokine-glycosaminoglycan interactions

Glycosaminoglycans (GAGs) bind a large array of proteins and mediate fundamental and diverse roles in human physiology. Ion pair interactions between protein lysines/arginines and GAG sulfates/carboxylates mediate binding. Neutrophil-activating chemokines (NAC) are GAG-binding proteins, and their sequences reveal high selectivity for lysines over arginines indicating they are functionally not equivalent. NAC binding to GAGs impacts gradient formation, receptor functions, and endothelial activation, which together regulate different components of neutrophil migration. We characterized the consequence of mutating lysine to arginine in NAC CXCL8, a well-characterized GAG-binding protein. We chose three lysines — two highly conserved lysines (K20 and K64) and a CXCL8-specific lysine (K67). Interestingly, the double K64R/K20R and K64R/K67R mutants are highly impaired in recruiting neutrophils in a mouse model. Further, both the mutants bind GAG heparin with higher affinity but show similar receptor activity. NMR and MD studies indicate that the structures are essentially identical to the WT, but the mutations alter the network of intramolecular ion pair interactions. These observations collectively indicate that the reduced in vivo recruitment is due to altered GAG interactions, higher GAG binding affinity can be detrimental, and specificity of lysines fine-tunes in vivo GAG interactions and function.

Improving the thermostability by introduction of arginines on the surface of α-L-rhamnosidase (r-Rha1) from Aspergillus niger

To improve the thermostability of α-L-rhamnosidase (r-Rha1), an enzyme previously identified from Aspergillus niger JMU-TS528, multiple arginine (Arg) residues were introduced into the r-Rha1 sequence to replace several lysine (Lys) residues that located on the surface of the folded r-Rha1. Hinted by in silico analysis, five surface Lys residues (K134, K228, K406, K440, K573) were targeted to produce a list of 5 single-residue mutants and 4 multiple-residue mutants using site-directed mutagenesis. Among these mutants, a double Lys to Arg mutant, i.e. K406R/K573R, showed the best thermostability improvement. The half-life of this mutant's enzyme activity increased 3 h at 60 °C, 23 min at 65 °C, and 3.5 min at 70 °C, when compared with the wild type. The simulated protein structure based interaction analysis and molecular dynamics calculation indicate that the thermostability improvement of the mutant K406R-K573R was possibly due to the extra hydrogen bonds, the additional cation-π interactions, and the relatively compact conformation. With the enhanced thermostability, the α-L-rhamnosidase mutant, K406R-K573R, has potentially broadened the r-Rha1 applications in food processing industry.

Automated Solid-Phase Protein Modification with Integrated Enzymatic Digest for Reaction Validation: Application of a Compartmented Microfluidic Reactor for Rapid Optimization and Analysis of Protein Biotinylation

Protein modification by covalent coupling of small ligands or markers is an important prerequisite for the use of proteins in many applications. Well-known examples are the use of proteins with fluorescent markers in many in vivo experiments or the binding of biotinylated antibodies via biotin-streptavidin coupling in the frame of numerous bioassays. Multiple protocols were established for the coupling of the respective molecules, e.g., via the C and N-terminus, or via cysteines and lysines exposed at the protein surface. Still, in most cases the conditions of these standard protocols are only an initial guess. Optimization of the coupling parameters like reagent concentrations, pH, or temperature may strongly increase coupling yield and the biological activity of the modified protein. In order to facilitate the process of optimizing coupling conditions, a method was developed which uses a compartmented microfluidic reactor for the rapid screening of different coupling conditions. In addition, the system allows for the integration of an enzymatic digest of the modified protein directly after modification. In combination with a subsequent MALDI-TOF analysis of the resulting fragments, this gives a fast and detailed picture not only of the number and extent of the generated modifications but also of their position within the protein sequence. The described process was demonstrated for biotinylation of green fluorescent protein. Different biotin-excesses and different pH-values were tested in order to elucidate the influence on the modification extent and pattern. In addition, the results of solid-phase based modifications within the microfluidic reactor were compared to modification patterns resulting from coupling trials with unbound protein. As expected, modification patterns of immobilized proteins showed clear differences to the ones of dissolved proteins.

Role of surface residue 184 in the catalytic activity of NADH oxidase from Streptococcus pyogenes

Nicotinamide adenine dinucleotide (NADH) oxidase from Streptococcus pyogenes (SpNox) is a flavoprotein harboring one molecule of noncovalently bound flavin adenine dinucleotide. It catalyzes the oxidation of NADH by reducing molecular O2 to H2O directly through a four-electron reduction. In this study, we selected the lysine residues on the surface of SpNox and mutated them into arginine residues to study the effect on the enzyme activity. A single-point mutation (K184R) at the surface of SpNox enhanced NADH oxidase activity by approximately 50 % and improved thermostability with 46.6 % longer half life at 30 °C. Further insights into the function of residue K184 were obtained by substituting it with other nonpolar, polar, positively charged, and negatively charged residues. To elucidate the role of this residue, computer-assisted molecular modeling and substrate docking were performed. The results demonstrate that even a single mutation at the surface of the enzyme induces changes in the interaction at the active site and affects the activity and stability. Additionally, the data also suggest that the K184R mutant can be used as an effective biocatalyst for NAD(+) regeneration in L-rare sugar production.