Cd2+-Induced Conformational Change of a Synthetic Metallopeptide: Slow Metal Binding Followed by a Slower Conformational Change

Natural and artificial proteins containing cadmium

This chapter describes an approach using designed proteins to understand the structure, spectroscopy, and dynamics of proteins that bind Cd(II). We will show that three-stranded coiled coils (3SCCs) based on the parent peptides TRI (Ac-G(LKALEEK)(4)G-NH(2)) or GRAND (Ac-G(LKALEEK)(5)G-NH(2)) have been essential for understanding how Cd(II) binds to thiolate-rich environments in proteins. Examples are given correlating physical properties such as the binding constants or deprotonation constants relating to structure. We present a scale that relates (113)Cd NMR chemical shifts to structures extracted from (111m)Cd PAC experiments. In addition, we describe motional processes that help transport from the helical interface of proteins into the hydrophobic interior of helical bundles. These studies help clarify the chemistry of Cd(II) in relation to metal-regulated gene expression and detoxification.

Nanomedicine for targeted cancer therapy: towards the overcoming of drug resistance

Anticancer drug resistance almost invariably emerges and poses major obstacles towards curative therapy of various human malignancies. In the current review we will distinguish between mechanisms of chemoresistance that are predominantly mediated by ATP-driven multidrug resistance (MDR) efflux transporters, typically of the ATP-binding cassette (ABC) superfamily, and those that are independent of such drug efflux pumps. In recent years, multiple nanoparticle (NP)-based therapeutic systems have been developed that were rationally designed to overcome drug resistance by neutralizing, evading or exploiting various drug efflux pumps and other resistance mechanisms. NPs are being exploited for selective drug delivery to tumor cells, to cancer stem/tumor initiating cells and/or to the supportive cancer cell microenvironment, i.e. stroma or tumor vasculature. Some of these NPs are currently undergoing preclinical in vivo studies as well as advanced stages of clinical evaluation with promising results. Nanovehicles harboring a payload of therapeutic drug combinations for the selective targeting and elimination of tumor cells as well as the simultaneous overcoming of mechanisms of drug resistance are a subject of intense research efforts, some of which are expected to enter clinical trials in the near future. In the present review we highlight novel approaches to selectively target cancer cells and overcome drug resistance phenomena, through the use of various nanometric drug delivery systems. In the near future, it is anticipated that innovative theragnostic nanovehicles will be developed which will harbor four major components: (1) a selective targeting moiety, (2) a diagnostic imaging aid for the localization of the malignant tumor and its micro- or macrometastases, (3) a cytotoxic, small molecule drug(s) or novel therapeutic biological(s), and (4) a chemosensitizing agent aimed at neutralizing a resistance mechanism, or exploiting a molecular "Achilles hill" of drug resistant cells. We propose to name these envisioned four element-containing nanovehicle platform, "quadrugnostic" nanomedicine. This targeted strategy holds promise in paving the way for the introduction of highly effective nanoscopic vehicles for cancer therapeutics while overcoming drug resistance.

Metal ion binding to anticoagulation factor II from the venom of Agkistrodon acutus: stabilization of the structure and regulation of the binding affinity to activated coagulation factor X

Anticoagulation factor II (ACF II) isolated from the venom of Agkistrodon acutus is an activated coagulation factor X (FXa)-binding protein with both anticoagulant and hypotensive activities. The thermodynamics of the binding of alkaline earth metal ions to ACF II and their effects on the stability of ACF II and the binding of ACF II to FXa were investigated by isothermal titration calorimetry, fluorescence, differential scanning calorimetry, and surface plasmon resonance. The binding of ACF II to FXa does not have an absolute requirement for Ca(2+). Mg(2+), Sr(2+), and Ba(2+) can induce the binding of ACF II to FXa. The radii of the cations bound in ACF II crucially affect the binding affinity of ACF II for cations and the structural stability of ACF II against guanidine hydrochloride and thermal denaturation, whereas the radii of cations bound in FXa markedly affect the binding affinity between ACF II and FXa. The binding affinities of ACF II for cations and the capacities of metal-induced stabilization of ACF II follow the same trend: Ca(2+) > Sr(2+) > Ba(2+). The metal-induced binding affinities of ACF II for FXa follow the trend Mg(2+) > Ca(2+) > Sr(2+) > Ba(2+). Although Mg(2+) shows significantly low binding affinity with ACF II, Mg(2+) is the most effective to induce the binding of ACF II with FXa. Our observations suggest that in blood the bindings of Ca(2+) in two sites of ACF II increase the structural stability of ACF II, but these bindings are not essential for the binding of ACF II with FXa, and that the binding of Mg(2+) and Ca(2+) to FXa may be essential for the recognition between FXa and ACF II. Like Ca(2+), the abundant Mg(2+) in blood also plays an important role in the anticoagulation of ACF II.

Design of multispecific protein sequences using probabilistic graphical modeling

In nature, proteins partake in numerous protein- protein interactions that mediate their functions. Moreover, proteins have been shown to be physically stable in multiple structures, induced by cellular conditions, small ligands, or covalent modifications. Understanding how protein sequences achieve this structural promiscuity at the atomic level is a fundamental step in the drug design pipeline and a critical question in protein physics. One way to investigate this subject is to computationally predict protein sequences that are compatible with multiple states, i.e., multiple target structures or binding to distinct partners. The goal of engineering such proteins has been termed multispecific protein design. We develop a novel computational framework to efficiently and accurately perform multispecific protein design. This framework utilizes recent advances in probabilistic graphical modeling to predict sequences with low energies in multiple target states. Furthermore, it is also geared to specifically yield positional amino acid probability profiles compatible with these target states. Such profiles can be used as input to randomly bias high-throughput experimental sequence screening techniques, such as phage display, thus providing an alternative avenue for elucidating the multispecificity of natural proteins and the synthesis of novel proteins with specific functionalities. We prove the utility of such multispecific design techniques in better recovering amino acid sequence diversities similar to those resulting from millions of years of evolution. We then compare the approaches of prediction of low energy ensembles and of amino acid profiles and demonstrate their complementarity in providing more robust predictions for protein design.

Harnessing natures ability to control metal ion coordination geometry using de novo designed peptides

Advances in protein chemistry and molecular and structural biology have empowered modern chemists to build complex biological architectures using a "first principles" approach, which is known as de novo protein design. In this Perspective we demonstrate how simple three-stranded alpha-helical constructs can be prepared by the sole consideration of the primary amino acid sequence of a peptide. With these well defined systems, we then demonstrate that metal binding cavities can be carved out of the hydrophobic cores of these aggregates in order to bind metal ions such as cadmium with well defined coordination geometries. Examples will be given of homoleptic CdS(3) complexes, CdS(3)O sites and proteins which contain equilibrium mixtures of these two species. We will provide a description of a strategy that allows us to build heterochromic peptides (small proteins that complex two metals in nearly identical environments but which result in different physical properties and allow for metal site selectivity). We conclude with a new class of designed peptides, diastereopeptides, which can exploit changes in amino acid chirality to control metal ion coordination number and lead to an alternative path towards heterochromic systems. The constructs described herein represent the initial steps of preparing protein structures that may simultaneous contain structural and catalytic metal binding centers. These studies inform the community on a developing field, which promises new opportunities for the study of bioinorganic chemistry.