Zrinka Karačić

A novel plant enzyme with dual activity: an atypical Nudix hydrolase and a dipeptidyl peptidase III

Abstract In a search for plant homologues of dipeptidyl peptidase III (DPP III) family, we found a predicted protein from the moss Physcomitrella patens (UniProt entry: A9TLP4), which shared 61% sequence identity with the Arabidopsis thaliana uncharacterized protein, designated Nudix hydrolase 3. Both proteins contained all conserved regions of the DPP III family, but instead of the characteristic hexapeptide HEXXGH zinc-binding motif, they possessed a pentapeptide HEXXH, and at the N-terminus, a Nudix box, a hallmark of Nudix hydrolases, known to act upon a variety of nucleoside diphosphate derivatives. To investigate their biochemical properties, we expressed heterologously and purified Physcomitrella (PpND) and Arabidopsis (AtND) protein. Both hydrolyzed, with comparable catalytic efficiency, the isopentenyl diphosphate (IPP), a universal precursor for the biosynthesis of isoprenoid compounds. In addition, PpND dephosphorylated four purine nucleotides (ADP, dGDP, dGTP, and 8-oxo-dATP) with strong preference for oxidized dATP. Furthermore, PpND and AtND showed DPP III activity against dipeptidyl-2-arylamide substrates, which they cleaved with different specificity. This is the first report of a dual activity enzyme, highly conserved in land plants, which catalyzes the hydrolysis of a peptide bond and of a phosphate bond, acting both as a dipeptidyl peptidase III and an atypical Nudix hydrolase.

Aspartate 496 from the subsite S2 drives specificity of human dipeptidyl peptidase III

Abstract Human dipeptidyl peptidase III (hDPP III) is a member of the M49 metallopeptidase family, which is involved in intracellular protein catabolism and oxidative stress response. To investigate the structural basis of hDPP III preference for diarginyl arylamide, using site-directed mutagenesis, we altered its S2 subsite to mimic the counterpart in yeast enzyme. Kinetic studies revealed that the single mutant D496G lost selectivity due to the increase of the Km value. The D496G, but not S504G, showed significantly decreased binding of peptides with N-terminal arginine, and of tynorphin. The results obtained identify Asp496 as an important determinant of human DPP III substrate specificity.

Molecular determinants of human dipeptidyl peptidase III sensitivity to thiol modifying reagents

Abstract Human dipeptidyl peptidase III (DPP III) is a member of the metallopeptidase family M49, involved in protein metabolism and oxidative stress response. DPP III crystal structure shows the two lobe-like domains separated by a wide cleft. The human enzyme has a total of six cysteines, three in the lower (Cys19, Cys147, and Cys176) and three in the upper (Cys509, Cys519, and Cys654), catalytic, domain containing the active-site zinc ion. To elucidate the molecular basis of this enzyme’s susceptibility to sulfhydryl reagents, biochemical analysis of a set of Cys to Ala mutants was used, supported by mass spectrometry. Cys176, a residue 44 Å apart from the catalytic center of the ligand-free enzyme, was found responsible for the inactivation with the submicromolar concentration of an organomercurial compound, and three additional cysteines contri\xadbuted to sensitivity to aromatic disulfides. Upon treatment with oxidized glutathione [glutathione disulfide (GSSG)], cysteine residues at positions 147, 176, and 654 were found glutathionylated. The mutational analysis confirmed the involvement of Cys176 and Cys654 in human DPP III inactivation by GSSG. Observation that Cys176, a residue quite distant from the active center, contributes to enzyme inactivation, indicates that the substrate-binding site of human DPP III comprises both lower and upper protein domain.

New findings about human dipeptidyl peptidase III based on mutations found in cancer

Dipeptidyl peptidase III (DPP III) is a cytosolic enzyme belonging to the metallopeptidase family M49, involved in the final steps of protein catabolism. More than a hundred missense mutations can be found in the coding region of the human DPP3 gene when searching cBioPortal for Cancer Genomics. The role of two highly conserved residues in the family M49, whose mutations G313W and R510W were detected in human cancer, was investigated using combined experimental and computational approaches (substrate docking and MD simulations). Several mutants of human DPP III were expressed and purified as recombinant proteins, and their biochemical properties were determined. The conservative substitution of Arg510 with lysine mildly decreased enzyme activity activity for Arg-Arg-2-naphtylamide substrate, while the substitutions of Arg510 with glutamine and Gly313 with alanine substantially decreased enzyme activity, and tryptophan substitutions found in cancer, G313W and R510W, almost abolished enzyme activity. MD simulations showed that substitution of Gly313, and especially Arg510 with tryptophan, significantly increases the enzyme flexibility, particularly that of the binding site including the H450ELLGH455 motif, and influences the substrate interactions with the catalytic His568. The results clearly indicate that, besides the enzyme structure, its dynamics properties also significantly influence the human DPP III activity.

A novel Porphyromonas gingivalis enzyme: An atypical dipeptidyl peptidase III with an ARM repeat domain

Porphyromonas gingivalis, an asaccharolytic Gram-negative oral anaerobe, is a major pathogen associated with adult periodontitis, a chronic infective disease that a significant percentage of the human population suffers from. It preferentially utilizes dipeptides as its carbon source, suggesting the importance of dipeptidyl peptidase (DPP) types of enzyme for its growth. Until now DPP IV, DPP5, 7 and 11 have been extensively investigated. Here, we report the characterization of DPP III using molecular biology, biochemical, biophysical and computational chemistry methods. In addition to the expected evolutionarily conserved regions of all DPP III family members, PgDPP III possesses a C-terminal extension containing an Armadillo (ARM) type fold similar to the AlkD family of bacterial DNA glycosylases, implicating it in alkylation repair functions. However, complementation assays in a DNA repair-deficient Escherichia coli strain indicated the absence of alkylation repair function for PgDPP III. Biochemical analyses of recombinant PgDPP III revealed activity similar to that of DPP III from Bacteroides thetaiotaomicron, and in the range between activities of human and yeast counterparts. However, the catalytic efficiency of the separately expressed DPP III domain is ~1000-fold weaker. The structure and dynamics of the ligand-free enzyme and its complex with two different diarginyl arylamide substrates was investigated using small angle X-ray scattering, homology modeling, MD simulations and hydrogen/deuterium exchange (HDX). The correlation between the experimental HDX and MD data improved with simulation time, suggesting that the DPP III domain adopts a semi-closed or closed form in solution, similar to that reported for human DPP III. The obtained results reveal an atypical DPP III with increased structural complexity: its superhelical C-terminal domain contributes to peptidase activity and influences DPP III interdomain dynamics. Overall, this research reveals multifunctionality of PgDPP III and opens direction for future research of DPP III family proteins.

Validation of flavonoids as potential dipeptidyl peptidase III inhibitors: Experimental and computational approach.

Fifteen flavonoids were studied for their inhibitory activity against human dipeptidyl peptidase III (hDPP III) combining an in vitro assay with an in silico molecular modeling study. All analyzed flavonoids showed inhibitory effects against hDPP III with the IC50 values ranging from 22.0 to 437.2 μm. Our 3D QSAR studies indicate that the presence of hydrophilic regions at a flavonoid molecule increases its inhibitory activity, while the higher percentage of hydrophobic surfaces has negative impact on enzyme inhibition. Furthermore, molecular dynamics (MD) simulations of the complex of hDPP III with one of the most potent inhibitors, luteolin, were performed, and binding mode analysis revealed that the 3′ and 4′ hydroxyl group on B‐ring as well as 5 and 7 hydroxyl group on A‐ring helps luteolin to interact with the Asn391, Asn406, Tyr417, His450, Glu451, Val447, Glu512, Asn545, Gln566, and Arg572 residues. The MD results clearly provide valuable information explaining the importance of flavonoid hydroxyl groups in the mechanism for the binding pattern at the active site of hDPP III.

Fluorescent cyanine-guanidiniocarbonyl-pyrrole conjugate with pH-dependent DNA/RNA recognition and DPP III fluorescent labelling and inhibition properties

Here designed and prepared cyanine-guanidinocarbonyl-pyrrole conjugate (Cy-GCP), intrinsically non-fluorescent, revealed fluorescent switch-on recognition of various secondary structures of ds-DNA and ds-RNA. Moreover, at the same submicromolar concentrations, DNA/RNA recognition was observed by selective induced (I)CD pattern in the visible range. Preliminary results showed that Cy-GCP strongly interacted with DPP III enzyme, switching-on the fluorescence upon binding and inhibiting enzyme action with efficiency comparable to the best-known inhibitor tynorphin.Graphical abstract