Copper binding selectivity of N- and C-sites in serum (human)- and ovo-transferrin

Exploring high hydrostatic pressure effects on anthocyanin binding to serum albumin and food-derived transferrins

This study investigated the effects of high hydrostatic pressure (HHP) on the binding interactions of cyanindin-3-O-glucoside (C3G) to bovine serum albumin, human serum albumin (HSA), bovine lactoferrin, and ovotransferrin. Fluorescence quenching revealed that HHP reduced C3G-binding affinity to HSA, while having a largely unaffected role for the other proteins. Notably, pretreating HSA at 500 MPa significantly increased its dissociation constant with C3G from 24.7 to 34.3 μM. Spectroscopic techniques suggested that HSA underwent relatively pronounced tertiary structural alterations after HHP treatments. The C3G-HSA binding mechanisms under pressure were further analyzed through molecular dynamics simulation. The localized structural changes in HSA under pressure might weaken its interaction with C3G, particularly polar interactions such as hydrogen bonds and electrostatic forces, consequently leading to a decreased binding affinity. Overall, the importance of pressure-induced structural alterations in proteins influencing their binding with anthocyanins was highlighted, contributing to optimizing HHP processing for anthocyanin-based products.

A conserved asparagine residue stabilizes iron binding in Manduca sexta transferrin-1

Transferrin 1 (Tsf1) is an insect-specific iron-binding protein that is abundant in hemolymph and other extracellular fluids. It binds iron tightly at neutral pH and releases iron under acidic conditions. Tsf1 influences the distribution of iron in the body and protects against infection. Elucidating the mechanisms by which Tsf1 achieves these functions will require an understanding of how Tsf1 binds and releases iron. Previously, crystallized Tsf1 from Manduca sexta was shown to have a novel type of iron coordination that involves four iron-binding ligands: two tyrosine residues (Tyr90 and Tyr204), a buried carbonate anion, and a solvent-exposed carbonate anion. The solvent-exposed carbonate anion was bound by a single amino acid residue, a highly conserved asparagine at position 121 (Asn121); thus, we predicted that Asn121 would be essential for high-affinity iron binding. To test this hypothesis, we analyzed the iron-binding and -release properties of five forms of recombinant Tsf1: wild-type, a Y90F/Y204F double mutant (negative control), and three Asn121 mutants (N121A, N121D and N121S). Each of the Asn121 mutants exhibited altered spectral properties, confirming that Asn121 contributes to iron coordination. The N121D and N121S mutations resulted in slightly lower affinity for iron, especially at acidic pH, while iron binding and release by the N121A mutant was indistinguishable from that of the wild-type protein. The surprisingly minor consequences of mutating Asn121, despite its high degree of conservation in diverse insect species, suggest that Asn121 may play a role that is essential in vivo but non-essential for high affinity iron binding in vitro.

Understanding the pH-dependent interaction of anthocyanin with two food-derived transferrins

The potential binding of cyanidin-3-O-glucoside (C3G) to bovine lactoferrin (BLF) and ovotransferrin (OTF) at pH 3, 5, and 7 was investigated for the first time. Multiple spectroscopic techniques demonstrated pH-dependent alterations in the conformational characteristics of BLF and OTF upon complexation with C3G. Fluorescence quenching assays showed that their highest binding affinity was at pH 7. Hydrophobic interactions and hydrogen bonds were found to be crucial in molecular dynamics simulations but with significantly lower probabilities of formation at pH 3 (p < 0.05). At pH 7, electrostatic attraction can occur for the negatively charged forms of C3G, and the well-maintained native structures of BLF and OTF may be favorable for stabilizing the C3G binding sites. This study sheds light on the stronger interaction of C3G with BLF/OTF at pH 7, which may have implications for future applications such as anthocyanin stabilization or the development of functional food ingredients.

Superstoichiometric Binding of the Anticancer Agent Titanocene Dichloride by Human Serum Transferrin and the Accompanying Lobe Closure

Titanocene dichloride (TDC) is an anticancer agent that delivers Ti(IV) into each of the two Fe(III) binding sites of bilobal human serum transferrin (Tf). This protein has been implicated in the selective transport of Ti(IV) to cells. How Ti(IV) might be released from the Tf Fe(III) binding site has remained a question, and crystal structures have raised issues about lobe occupancy and lobe closure in Ti(IV)-loaded Tf, compared with the Fe(III)-loaded form. Here, inductively coupled plasma optical emission spectroscopy reveals that Tf can stabilize toward hydrolytic precipitation more than 2 equiv of Ti, implying superstoichiometric binding beyond the two Fe(III) binding sites. Further studies support the inability of TDC to induce a complete lobe closure of Tf. Fluorescence data for TDC binding at low equivalents of TDC support an initial protein conformational change and lobe closure upon Ti binding, whereas data at higher equivalents support an open lobe configuration. Spectroscopic titration reveals less intense protein-metal electronic transitions as TDC equivalents are increased. Denaturing urea-PAGE gels and small angle X-ray scattering studies support an open lobe conformation. The concentrations of bicarbonate used in some earlier studies are demonstrated here to cause a pH change over time, which may contribute to variation in the apparent molar absorptivity associated with Ti(IV) binding in the Fe binding site. Finally, Fe(III)-bound holo-Tf still stabilizes TDC toward hydrolytic precipitation, a finding that underscores the importance of the interactions of Tf and TDC outside the Fe(III) binding site and suggests possible new pathways of Ti introduction to cells.

Protein-Based Nanomedicine for Therapeutic Benefits of Cancer

Proteins, a type of natural biopolymer that possess many prominent merits, have been widely utilized to engineer nanomedicine for fighting against cancer. Motivated by their ever-increasing attention in the scientific community, this review aims to provide a comprehensive showcase on the current landscape of protein-based nanomedicine for cancer therapy. On the basis of role differences of proteins in nanomedicine, protein-based nanomedicine engineered with protein therapeutics, protein carriers, enzymes, and composite proteins is introduced. The cancer therapeutic benefits of the protein-based nanomedicine are also discussed, including small-molecular therapeutics-mediated therapy, macromolecular therapeutics-mediated therapy, radiation-mediated therapy, reactive oxygen species-mediated therapy, and thermal effect-mediated therapy. Lastly, future developments and potential challenges of protein-based nanomedicine are elucidated toward clinical translation. It is believed that protein-based nanomedicine will play a vital role in the battle against cancer. We hope that this review will inspire extensive research interests from diverse disciplines to further push the developments of protein-based nanomedicine in the biomedical frontier, contributing to ever-greater medical advances.

The Role of Ovotransferrin in Egg-White Antimicrobial Activity: A Review

Eggs are a whole food which affordably support human nutritional requirements worldwide. Eggs strongly resist bacterial infection due to an arsenal of defensive systems, many of which reside in the egg white. However, despite improved control of egg production and distribution, eggs remain a vehicle for foodborne transmission of Salmonella enterica serovar Enteritidis, which continues to represent a major public health challenge. It is generally accepted that iron deficiency, mediated by the iron-chelating properties of the egg-white protein ovotransferrin, has a key role in inhibiting infection of eggs by Salmonella. Ovotransferrin has an additional antibacterial activity beyond iron-chelation, which appears to depend on direct interaction with the bacterial cell surface, resulting in membrane perturbation. Current understanding of the antibacterial role of ovotransferrin is limited by a failure to fully consider its activity within the natural context of the egg white, where a series relevant environmental factors (such as alkalinity, high viscosity, ionic composition, and egg white protein interactions) may exert significant influence on ovotransferrin activity. This review provides an overview of what is known and what remains to be determined regarding the antimicrobial activity of ovotransferrin in egg white, and thus enhances understanding of egg safety through improved insight of this key antimicrobial component of eggs.

Theoretical insights into the competitive metal bioaffinity of lactoferrin as a metal ion carrier: a DFT study

Metal–protein complexes, specifically lactoferrin (Lf), an iron-binding glycoprotein found naturally in milk and several other body fluids play a pivotal role in all living organisms.

Benzothiazole based multi-analyte sensor for selective sensing of Zn2+and Cd2+and subsequent sensing of inorganic phosphates (Pi) in mixed aqueous medium

A multi-analyte sensor selectively senses Zn²⁺and Cd²⁺ions and subsequently responds to phosphates in mixed aqueous medium.

Aggregation deaggregation influenced selective and sensitive detection of Cu2+ and ATP by histidine functionalized water-soluble fluorescent perylene diimide under physiological conditions and in living cells

A novel PDI-HIS probe detects Cu²⁺ to form aggregated nonfluorescent complex. Addition of 0.58 ppm ATP to this complex causes its rapid disaggregation thereby recovering the fluorescence by ∼99% in vitro and in A549 living cells.

Rational design of a new fluorescent ‘ON/OFF’ xanthene dye for phosphate detection in live cells

A new fluorescein derivative with ON/OFF features, 9-[1-(4-tert-butyl-2-methoxyphenyl)]-6-hydroxy-3H-xanthen-3-one (Granada Green, GG), was designed and synthesised.

An ATP-selective, lanthanide complex luminescent probe

A luminescent probe based on a europium complex is developed, which effectively distinguishes adenosine-5'-triphosphate (ATP) from adenosine diphosphate (ADP) and adenosine monophosphate (AMP) in pure water at pH 6.8. With a longer lifetime (in ms range), the probe is prospectively applied to biological systems to monitor ATP levels by completely removing the background fluorescence of other molecules.

Simple but Effective Way to Sense Pyrophosphate and Inorganic Phosphate by Fluorescence Changes

A new fluorescent chemosensor based on the acridine-Zn(II) derivative effectively recognizes pyrophosphate and inorganic phosphate at pH 7.4. Acridine derivative 1 displayed a fluorescent quenching effect with pyrophosphate; on the other hand, a large fluorescent enhancement was observed with inorganic phosphate. [structure: see text].

Demonstration of a hyperglycemia-driven pathogenic abnormality of copper homeostasis in diabetes and its reversibility by selective chelation: quantitative comparisons between the biology of copper and eight other nutritionally essential elements in normal and diabetic individuals

We recently showed that treatment with the Cu(II)-selective chelator, trientine, alleviates heart failure in diabetic rats, improves left ventricular hypertrophy in humans with type 2 diabetes, and increases urinary Cu excretion in both diabetic rats and humans compared with nondiabetic control subjects. In this study, we characterized the homeostasis of Cu and eight other nutritionally essential elements in diabetes under fully residential conditions in male subjects with type 2 diabetes and age-matched control subjects. We then probed elemental balance with oral trientine in a parallel-group, placebo-controlled study in these subjects. Before treatment, there were no detectable between-group differences in the balance of any element, although urinary output of several elements was greater in diabetic subjects. Mean extracellular superoxide dismutase (EC-SOD) activity was elevated in diabetic subjects, and its activity correlated strongly with the interaction between [Cu]serum and HbA1c. Trientine caused the Cu balance to become negative in diabetic subjects through elevated urinary Cu losses and suppressed elevated EC-SOD. Basal urinary Cu predicted urinary Cu losses during treatment, which caused extraction of systemic Cu(II). We suggest that cardiovascular complications in diabetes might be better controlled by therapeutic strategies that focus on lowering plasma glucose and loosely bound systemic Cu(II).

Kinetics of metal ion exchange between citric acid and serum transferrin

The exchange of Fe(3+), Tb(3+), In(3+), Ga(3+), and Al(3+) between the C-terminal metal-binding site of the serum iron transport protein transferrin and the low-molecular-mass serum chelating agent citrate has been studied at pH 7.4 and 25 degrees C. The removal of Ga(3+), In(3+), and Al(3+) follows simple saturation kinetics with respect to the citrate concentration. In contrast, removal of both Fe(3+) and Tb(3+) shows a combination of saturation and first-order kinetic behavior with respect to the citrate concentration. The saturation component is consistent with a mechanism for metal release in which access to the bound metal is controlled by a rate-limiting conformational change in the protein. The first-order kinetic pathway is very rapid for Tb(3+), and this is attributed to a direct attack of the citrate on the Tb(3+) ion within the closed protein conformation. It is suggested that this pathway is more readily available for Tb(3+) because of the larger coordination number for this cation and the presence of an aquated coordination site in the Tb(3+)-CO(3)-Tf ternary complex. There is relatively little variation in the k(max) values for the saturation pathway for Tb(3+), Ga(3+), Al(3+), and In(3+), but the k(max) value for Fe(3+) is significantly smaller. It is suggested that protein interactions across the interdomain cleft of transferrin largely control the release of the first group of metal ions, while the breaking of stronger metal-protein bonds slows the rate of iron release. The rates of metal binding to apotransferrin are clearly controlled in large part by the hydrolytic tendencies of the free metal ions. For the more amphoteric metal ions Al(3+) and Ga(3+), there is rapid protein binding, and the addition of citrate actually retards this reaction. In contrast, the nonamphoteric In(3+) ion binds very slowly in the absence of citrate, presumably due to the rapid formation of polymeric In-hydroxo complexes upon addition of the unchelated metal ion to the pH 7.4 protein solution. The addition of citrate to the reaction accelerates the binding of In(3+) to apoTf, presumably by forming soluble, mononuclear In-citrate complexes.

Dipeptidyl peptidase III is a zinc metallo-exopeptidase. Molecular cloning and expression

We have purified dipeptidyl peptidase III (EC 3.4.14.4) from human placenta. It had a pH optimum of 8.8 and readily hydrolysed Arg-Arg-beta-naphthylamide. Monoamino acid-, Gly-Phe-, Gly-Pro- and Bz-Arg-beta-naphthylamides were not hydrolysed at all. The enzyme was inhibited by p-chloromercuriphenylsulphonic acid, metal chelators and 3,4-dichloroisocoumarin and contained 1 mol of zinc per mol of enzyme. The zinc dissociation constant was 250 fM at pH 7. 4 as determined by the zinc binding study. We isolated, by immunological screening of a Uni-ZAP XR cDNA library constructed from rat liver mRNA species, a cDNA clone with 2633 bp encoding the rat enzyme. The longest open reading frame encodes a 827-residue protein with a theoretical molecular mass of 92790 Da. Escherichia coli SOLR cells were infected with the pBluescript phagemid containing the cloned cDNA and established the overexpression of a protein that hydrolysed Arg-Arg-beta-naphthylamide. The recombinant protein was purified and the amino acid sequence of the protein was confirmed. We presumed that the putative zinc-binding domain involved in catalysis was present in the recombinant enzyme. It was a novel zinc-binding motif in that one amino acid residue was inserted into the conserved HEXXH motif characteristic of the metalloproteinases.

Inequivalence of the two tyrosine ligands in the N-lobe of human serum transferrin

Human serum transferrin N-lobe (hTF/2N) has four iron-binding ligands, including one histidine, one aspartate, and two tyrosines. The present report elucidates the inequivalence of the two tyrosine ligands (Tyr 95 and Tyr 188) on the metal-binding properties of hTF/2N by means of site-directed mutagenesis, metal release kinetics, and absorption and electron paramagnetic resonance (EPR) spectroscopies. When the liganding tyrosines were mutated individually to phenylalanine, the resulting mutant Y95F showed a weak binding affinity for iron and no affinity for copper, whereas, mutant Y188F completely lost the ability to bind iron but formed a stable complex with copper. Since other studies have demonstrated that mutations of the other two ligands, histidine and aspartate, did not completely abolish iron binding, the present findings suggest that the tyrosine ligand at position 188 is essential for binding of iron to occur. Replacement of Tyr 188 with phenylalanine created a favorable chemical environment for copper coordination but a fatal situation for iron binding. The positions of the two liganding tyrosines in the metal-binding cleft suggest a reason for the inequivalence.