Design, Synthesis, and Evaluation of Polyamine Deacetylase Inhibitors, and High-Resolution Crystal Structures of Their Complexes with Acetylpolyamine Amidohydrolase

Cryo-EM structure and rational engineering of a superefficient ochratoxin A-detoxifying amidohydrolase

Ochratoxin A (OTA) is among the most prevalent mycotoxins detected in agroproducts, posing serious threats to human and livestock health. Using enzymes to conduct OTA detoxification is an appealing potential strategy. The recently identified amidohydrolase from Stenotrophomonas acidaminiphila, termed ADH3, is the most efficient OTA-detoxifying enzyme reported thus far and can hydrolyze OTA to nontoxic ochratoxin α (OTα) and L-β-phenylalanine (Phe). To elucidate the catalytic mechanism of ADH3, we solved the single-particle cryo-electron microscopy (cryo-EM) structures of apo-form, Phe- and OTA-bound ADH3 to an overall resolution of 2.5-2.7 Å. The role of OTA-binding residues was investigated by structural, mutagenesis and biochemical analyses. We also rationally engineered ADH3 and obtained variant S88E, whose catalytic activity was elevated by 3.7-fold. Structural analysis of variant S88E indicates that the E88 side chain provides additional hydrogen bond interactions to the OTα moiety. Furthermore, the OTA-hydrolytic activity of variant S88E expressed in Pichia pastoris is comparable to that of Escherichia coli-expressed enzyme, revealing the feasibility of employing the industrial yeast strain to produce ADH3 and its variants for further applications. These results unveil a wealth of information about the catalytic mechanism of ADH3-mediated OTA degradation and provide a blueprint for rational engineering of high-efficiency OTA-detoxifying machineries.

Properties and biotechnological applications of microbial deacetylase

Deacetylases, a class of enzymes that can catalyze the hydrolysis of acetylated substrates to remove the acetyl group, used in producing various products with high qualities, are one of the most influential industrial enzymes. These enzymes are highly specific, non-toxic, sustainable, and eco-friendly biocatalysts. Deacetylases and deacetylated compounds have been widely applicated in pharmaceuticals, medicine, food, and the environment. This review synthetically summarizes deacetylases' sources, characterizations, classifications, and applications. Moreover, the typical structural characteristics of deacetylases from different microbial sources are summarized. We also reviewed the deacetylase-catalyzed reactions for producing various deacetylated compounds, such as chitosan-oligosaccharide (COS), mycothiol, 7-aminocephalosporanic acid (7-ACA), glucosamines, amino acids, and polyamines. It is aimed to expound on the advantages and challenges of deacetylases in industrial applications. Moreover, it also serves perspectives on obtaining promising and innovative biocatalysts for enzymatic deacetylation. KEYPOINTS: • The fundamental properties of microbial deacetylases of various microorganisms are presented. • The biochemical characterizations, structures, and catalyzation mechanisms of microbial deacetylases are summarized. • The applications of microbial deacetylases in food, pharmaceutical, medicine, and the environment were discussed.

Strategies To Design Selective Histone Deacetylase Inhibitors

This review classifies drug-design strategies successfully implemented in the development of histone deacetylase (HDAC) inhibitors, which have many applications including cancer treatment. Our focus is on especially demanded selective HDAC inhibitors and their structure-activity relationships in relation to corresponding protein structures. The main part of the paper is divided into six subsections each narrating how optimization of one of six structural features can influence inhibitor selectivity. It starts with the impact of the zinc binding group on selectivity, continues with the optimization of the linker placed in the substrate binding tunnel as well as the adjustment of the cap group interacting with the surface of the protein, and ends with the addition of groups targeting class-specific sub-pockets: the side-pocket-, lower-pocket- and foot-pocket-targeting groups. The review is rounded off with a conclusion and an outlook on the future of HDAC inhibitor design.

Binding of N8-Acetylspermidine Analogues to Histone Deacetylase 10 Reveals Molecular Strategies for Blocking Polyamine Deacetylation

Eukaryotic histone deacetylase 10 (HDAC10) is a Zn²⁺-dependent hydrolase that exhibits catalytic specificity for the hydrolysis of the polyamine N⁸-acetylspermidine. The recently determined crystal structure of HDAC10 from Danio rerio (zebrafish) reveals a narrow active site cleft and a negatively charged "gatekeeper" (E274) that favors the binding of the slender cationic substrate. Because HDAC10 expression is upregulated in advanced-stage neuroblastoma and induces autophagy, the selective inhibition of HDAC10 suppresses the autophagic response and renders cancer cells more susceptible to cytotoxic chemotherapeutic drugs. Here, we describe X-ray crystal structures of zebrafish HDAC10 complexed with eight different analogues of N⁸-acetylspermidine. These analogues contain different Zn²⁺-binding groups, such as hydroxamate, thiolate, and the tetrahedral gem-diolate resulting from the addition of a Zn²⁺-bound water molecule to a ketone carbonyl group. Notably, the chemistry that accompanies the binding of ketonic substrate analogues is identical to the chemistry involved in the first step of catalysis, i.e., nucleophilic attack of a Zn²⁺-bound water molecule at the scissile carbonyl group of N⁸-acetylspermidine. The most potent inhibitor studied contains a thiolate Zn²⁺-binding group. These structures reveal interesting geometric changes in the metal coordination polyhedron that accommodate inhibitor binding. Additional interactions in the active site highlight features contributing to substrate specificity. These interactions are likely to contribute to inhibitor binding selectivity and will inform the future design of compounds selective for HDAC10 inhibition.

Structure and Function of the Acetylpolyamine Amidohydrolase from the Deep Earth Halophile Marinobacter subterrani

Polyamines are small organic cations that are essential for cellular function in all kingdoms of life. Polyamine metabolism is regulated by enzyme-catalyzed acetylation-deacetylation cycles in a fashion similar to the epigenetic regulation of histone function in eukaryotes. Bacterial polyamine deacetylases are particularly intriguing, because these enzymes share the fold and function of eukaryotic histone deacetylases. Recently, acetylpolyamine amidohydrolase from the deep earth halophile Marinobacter subterrani (msAPAH) was described. This Zn2+-dependent deacetylase shares 53% amino acid sequence identity with the acetylpolyamine amidohydrolase from Mycoplana ramosa (mrAPAH) and 22% amino acid sequence identity with the catalytic domain of histone deacetylase 10 from Danio rerio (zebrafish; zHDAC10), the eukaryotic polyamine deacetylase. The X-ray crystal structure of msAPAH, determined in complexes with seven different inhibitors as well as the acetate coproduct, shows how the chemical strategy of Zn2+-dependent amide hydrolysis and the catalytic specificity for cationic polyamine substrates is conserved in a subterranean halophile. Structural comparisons with mrAPAH reveal that an array of aspartate and glutamate residues unique to msAPAH enable the binding of one or more Mg2+ ions in the active site and elsewhere on the protein surface. Notwithstanding these differences, activity assays with a panel of acetylpolyamine and acetyllysine substrates confirm that msAPAH is a broad-specificity polyamine deacetylase, much like mrAPAH. The broad substrate specificity contrasts with the narrow substrate specificity of zHDAC10, which is highly specific for N8-acetylspermidine hydrolysis. Notably, quaternary structural features govern the substrate specificity of msAPAH and mrAPAH, whereas tertiary structural features govern the substrate specificity of zHDAC10.

Medicinal chemistry of metal chelating fragments in metalloenzyme active sites: A perspective

Numerous metal-containing enzymes (metalloenzymes) have been considered as drug targets related to diseases such as cancers, diabetes, anemia, AIDS, malaria, bacterial infection, fibrosis, and neurodegenerative diseases. Inhibitors of the metalloenzymes have been developed independently, most of which are mimics of substrates of the corresponding enzymes. However, little attention has been paid to the interactions between inhibitors and active site metal ions. This review is focused on different metal binding fragments and their chelating properties in the metal-containing active binding pockets of metalloenzymes. We have enumerated over one hundred of inhibitors targeting various metalloenzymes and identified over ten kinds of fragments with different binding patterns. Furthermore, we have investigated the inhibitors that are undergoing clinical evaluation in order to help looking for more potential scaffolds bearing metal binding fragments. This review will provide deep insights for the rational design of novel inhibitors targeting the metal-containing binding sites of specific proteins.

Polyamine Deacetylase Structure and Catalysis: Prokaryotic Acetylpolyamine Amidohydrolase and Eukaryotic HDAC10

Polyamines such as putrescine, spermidine, and spermine are small aliphatic cations that serve myriad biological functions in all forms of life. While polyamine biosynthesis and cellular trafficking pathways are generally well-defined, only recently has the molecular basis of reversible polyamine acetylation been established. In particular, enzymes that catalyze polyamine deacetylation reactions have been identified and structurally characterized: histone deacetylase 10 (HDAC10) from Homo sapiens and Danio rerio (zebrafish) is a highly specific N⁸-acetylspermidine deacetylase, and its prokaryotic counterpart, acetylpolyamine amidohydrolase (APAH) from Mycoplana ramosa, is a broad-specificity polyamine deacetylase. Similar to the greater family of HDACs, which mainly serve as lysine deacetylases, both enzymes adopt the characteristic arginase-deacetylase fold and employ a Zn²⁺-activated water molecule for catalysis. In contrast with HDACs, however, the active sites of HDAC10 and APAH are sterically constricted to enforce specificity for long, slender polyamine substrates and exclude bulky peptides and proteins containing acetyl-l-lysine. Crystal structures of APAH and D. rerio HDAC10 reveal that quaternary structure, i.e., dimer assembly, provides the steric constriction that directs the polyamine substrate specificity of APAH, whereas tertiary structure, a unique 3₁₀ helix defined by the P(E,A)CE motif, provides the steric constriction that directs the polyamine substrate specificity of HDAC10. Given the recent identification of HDAC10 and spermidine as mediators of autophagy, HDAC10 is rapidly emerging as a biomarker and target for the design of isozyme-selective inhibitors that will suppress autophagic responses to cancer chemotherapy, thereby rendering cancer cells more susceptible to cytotoxic drugs.

Lysine Acetylation Goes Global: From Epigenetics to Metabolism and Therapeutics

Post-translational acetylation of lysine residues has emerged as a key regulatory mechanism in all eukaryotic organisms. Originally discovered in 1963 as a unique modification of histones, acetylation marks are now found on thousands of nonhistone proteins located in virtually every cellular compartment. Here we summarize key findings in the field of protein acetylation over the past 20 years with a focus on recent discoveries in nuclear, cytoplasmic, and mitochondrial compartments. Collectively, these findings have elevated protein acetylation as a major post-translational modification, underscoring its physiological relevance in gene regulation, cell signaling, metabolism, and disease.

Histone deacetylase 10 structure and molecular function as a polyamine deacetylase

Cationic polyamines such as spermidine and spermine are critical in all forms of life, as they regulate the function of biological macromolecules. Intracellular polyamine metabolism is regulated by reversible acetylation and dysregulated polyamine metabolism is associated with neoplastic diseases such as colon cancer, prostate cancer and neuroblastoma. Here we report that histone deacetylase 10 (HDAC10) is a robust polyamine deacetylase, using recombinant enzymes from Homo sapiens (human) and Danio rerio (zebrafish). The 2.85 Å-resolution crystal structure of zebrafish HDAC10 complexed with a transition-state analogue inhibitor reveals that a glutamate gatekeeper and a sterically constricted active site confer specificity for N⁸-acetylspermidine hydrolysis and disfavour acetyllysine hydrolysis. Both HDAC10 and spermidine are known to promote cellular survival through autophagy. Accordingly, this work sets a foundation for studying the chemical biology of autophagy through the structure-based design of inhibitors that may also serve as new leads for cancer chemotherapy.

Polyamines bind to nucleic acids and their function is regulated by reversible acetylation. Here, the authors show that histone deacetylase 10 is a polyamine deacetylase and present its crystal structure with a bound polyamine transition state analogue inhibitor.

Structural aspects of HDAC8 mechanism and dysfunction in Cornelia de Lange syndrome spectrum disorders

Cornelia de Lange Syndrome (CdLS) encompasses a broad spectrum of phenotypes characterized by distinctive craniofacial abnormalities, limb malformations, growth retardation, and intellectual disability. CdLS spectrum disorders are referred to as cohesinopathies, with ∼70% of patients having a mutation in a gene encoding a core cohesin protein (SMC1A, SMC3, or RAD21) or a cohesin regulatory protein (NIPBL or HDAC8). Notably, the regulatory function of HDAC8 in cohesin biology has only recently been discovered. This Zn2+ -dependent hydrolase catalyzes the deacetylation of SMC3, a necessary step for cohesin recycling during the cell cycle. To date, 23 different missense mutants in the gene encoding HDAC8 have been identified in children with developmental features that overlap those of CdLS. Enzymological, biophysical, and structural studies of CdLS HDAC8 protein mutants have yielded critical insight on compromised catalysis in vitro. Most CdLS HDAC8 mutations trigger structural changes that directly or indirectly impact substrate binding and catalysis. Additionally, several mutations significantly compromise protein thermostability. Intriguingly, catalytic activity in many HDAC8 mutants can be partially or fully restored by an N-acylthiourea activator, suggesting a plausible strategy for the chemical rescue of compromised HDAC8 catalysis in vivo.

Biochemical and structural characterization of HDAC8 mutants associated with Cornelia de Lange syndrome spectrum disorders

Cornelia de Lange Syndrome (CdLS) spectrum disorders are characterized by multiple organ system congenital anomalies that result from mutations in genes encoding core cohesin proteins SMC1A, SMC3, and RAD21, or proteins that regulate cohesin function such as NIPBL and HDAC8. HDAC8 is the Zn(2+)-dependent SMC3 deacetylase required for cohesin recycling during the cell cycle, and 17 different HDAC8 mutants have been identified to date in children diagnosed with CdLS. As part of our continuing studies focusing on aberrant HDAC8 function in CdLS, we now report the preparation and biophysical evaluation of five human HDAC8 mutants: P91L, G117E, H180R, D233G, and G304R. Additionally, the double mutants D233G-Y306F and P91L-Y306F were prepared to enable cocrystallization of intact enzyme-substrate complexes. X-ray crystal structures of G117E, P91L-Y306F, and D233G-Y306F HDAC8 mutants reveal that each CdLS mutation causes structural changes that compromise catalysis and/or thermostability. For example, the D233G mutation disrupts the D233-K202-S276 hydrogen bond network, which stabilizes key tertiary structure interactions, thereby significantly compromising thermostability. Molecular dynamics simulations of H180R and G304R HDAC8 mutants suggest that the bulky arginine side chain of each mutant protrudes into the substrate binding site and also causes active site residue Y306 to fluctuate away from the position required for substrate activation and catalysis. Significantly, the catalytic activities of most mutants can be partially or fully rescued by the activator N-(phenylcarbamothioyl)-benzamide, suggesting that HDAC8 activators may serve as possible leads in the therapeutic management of CdLS.