The hydantoin transporter Mhp1 is a sodium-coupled secondary active transport protein of the nucleobase-cation-symport family and a member of the widespread 5-helix inverted repeat superfamily of transporters. The structure of Mhp1 was previously solved in three different conformations providing insight into the molecular basis of the alternating access mechanism. Here, we elucidate detailed events of substrate binding, through a combination of crystallography, molecular dynamics, site-directed mutagenesis, biochemical/biophysical assays, and the design and synthesis of novel ligands. We show precisely where 5-substituted hydantoin substrates bind in an extended configuration at the interface of the bundle and hash domains. They are recognised through hydrogen bonds to the hydantoin moiety and the complementarity of the 5-substituent for a hydrophobic pocket in the protein. Furthermore, we describe a novel structure of an intermediate state of the protein with the external thin gate locked open by an inhibitor, 5-(2-naphthylmethyl)-L-hydantoin, which becomes a substrate when leucine 363 is changed to an alanine. We deduce the molecular events that underlie acquisition and transport of a ligand by Mhp1.
The development of resistance to all current antibiotics in the clinic means there is an urgent unmet need for novel antibacterial agents with new modes of action. One of the best ways of finding these is to identify new essential bacterial enzymes to target. The advent of a number of in silico tools has aided classical methods of discovering new antibacterial targets and these programs are the subject of this review. Many of these tools apply a cheminformatic approach, utilising the structural information of either ligand or protein, chemogenomic databases and docking algorithms to identify putative antibacterial targets. Considering the wealth of potential drug targets identified from genomic research these approaches are perfectly placed to mine this rich resource, and complement drug discovery programmes. This article is protected by copyright. All rights reserved.
cAMP mediates autonomic regulation of heart rate by means of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, which underlie the pacemaker current If. cAMP binding to the C-terminal cyclic nucleotide binding domain enhances HCN open probability through a conformational change that reaches the pore via the C-linker. Using structural and functional analysis, we identified a binding pocket in the C-linker of HCN4. Cyclic dinucleotides, an emerging class of second messengers in mammals, bind the C-linker pocket (CLP) and antagonize cAMP regulation of the channel. Accordingly, cyclic dinucleotides prevent cAMP regulation of If in sinoatrial node myocytes, reducing heart rate by 30%. Occupancy of the CLP hence constitutes an efficient mechanism to hinder ?-adrenergic stimulation on If. Our results highlight the regulative role of the C-linker and identify a potential drug target in HCN4. Furthermore, these data extend the signaling scope of cyclic dinucleotides in mammals beyond their first reported role in innate immune system.
In recent years bacterial resistance has been observed against many of our current antibiotics, for instance most worryingly against the cephalosporins which are typically the last line of defence against many bacterial infections. Additionally the failure of high throughput screening in the discovery of new antibacterial drug leads has led to a decline in the number of antibacterial agents reaching the market. Alternative methods of drug discovery including structure based drug design are needed to meet the threats caused by the emergence of resistance. In this review we explore the latest advancements in the identification of new antibacterial agents through the use of a number of structure based drug design programs.
The modern era of antibacterial chemotherapy began in the 1930s, and the next four decades saw the discovery of almost all the major classes of antibacterial agents that are currently in use. However, bacterial resistance to many of these drugs is becoming an increasing problem. As such, the discovery of drugs with novel modes of action will be vital to meet the threats created by the emergence of resistance. Success in discovering inhibitors using high-throughput screening of chemical libraries is rare. In this Review we explore the exciting opportunities for antibacterial-drug discovery arising from structure-based drug design.
Staphylococcus aureus and a number of other Gram-positive organisms harbour two genes (murA and murZ) encoding UDP-N-acetylglucosamine enolpyruvyl transferase activity for catalysing the first committed step of peptidoglycan biosynthesis. We independently inactivated murA and murZ in S. aureus and established that either can sustain viability. Purification and characterization of the MurA and MurZ enzymes indicated that they are biochemically similar in vitro, consistent with similar overall structures predicted for the isozymes by molecular modelling. Nevertheless, MurA appears to be the primary enzyme utilized in the staphylococcal cell. Accordingly, murA expression was approximately five times greater than murZ expression during exponential growth, and the peptidoglycan content of S. aureus was reduced by approximately 25% following inactivation of murA, but remained almost unchanged following inactivation of murZ. Despite low level expression during normal growth, murZ expression was strongly induced (up to sixfold) following exposure to inhibitors of peptidoglycan biosynthesis, which was not observed for murA. Strains generated in this study were validated as potential tools for identifying novel anti-staphylococcal agents targeting peptidoglycan biosynthesis using known inhibitors of the pathway.
Membrane proteins are intrinsically involved in both human and pathogen physiology, and are the target of 60% of all marketed drugs. During the past decade, advances in the studies of membrane proteins using X-ray crystallography, electron microscopy and NMR-based techniques led to the elucidation of over 250 unique membrane protein crystal structures. The aim of the European Drug Initiative for Channels and Transporter (EDICT) project is to use the structures of clinically significant membrane proteins for the development of lead molecules. One of the approaches used to achieve this is a virtual high-throughput screening (vHTS) technique initially developed for soluble proteins. This paper describes application of this technique to the discovery of inhibitors of the leucine transporter (LeuT), a member of the neurotransmitter:sodium symporter (NSS) family.
Two voltage-dependent potassium channels, Kv1.1 (KCNA1) and Kv1.2 (KCNA2), are found to co-localize at the juxtaparanodal region of axons throughout the nervous system and are known to co-assemble in heteromultimeric channels, most likely in the form of the concatemer Kv1.1-1.2((3)) . Loss of the myelin sheath, as is observed in multiple sclerosis, uncovers the juxtaparanodal region of nodes of Ranvier in myelinated axons leading to potassium conductance, resulting in loss of nerve conduction. The selective blocking of these Kv channels is therefore a promising approach to restore nerve conduction and function. In the present study, we searched for novel inhibitors of Kv1.1-1.2((3)) by combining a virtual screening protocol and electrophysiological measurements on a concatemer Kv1.1-1.2((3)) stably expressed in Chinese hamster ovary K1 (CHO-K1) cells. The combined use of four popular virtual screening approaches (eHiTS, FlexX, Glide, and Autodock-Vina) led to the identification of several compounds as potential inhibitors of the Kv1.1-1.2((3)) channel. From 89 electrophysiologically evaluated compounds, 14 novel compounds were found to inhibit the current carried by Kv1.1-1.2((3)) channels by more than 80 % at 10 ?M. Accordingly, the IC(50) values calculated from concentration-response curve titrations ranged from 0.6 to 6 ?M. Two of these compounds exhibited at least 30-fold higher potency in inhibition of Kv1.1-1.2((3)) than they showed in inhibition of a set of cardiac ion channels (hERG, Nav1.5, and Cav1.2), resulting in a profile of selectivity and cardiac safety. The results presented herein provide a promising basis for the development of novel selective ion channel inhibitors, with a dramatically lower demand in terms of experimental time, effort, and cost than a sole high-throughput screening approach of large compound libraries.
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