Hidden Relationships between N-Glycosylation and Disulfide Bonds in Individual Proteins.

N-Glycosylation (NG) and disulfide bonds (DBs) are two prevalent co/post-translational modifications (PTMs) that are often conserved and coexist in membrane and secreted proteins involved in a large number of diseases. Both in the past and in recent times, the enzymes and chaperones regulating these PTMs have been constantly discovered to directly interact with each other or colocalize in the ER. However, beyond a few model proteins, how such cooperation affects N-glycan modification and disulfide bonding at selective sites in individual proteins is largely unknown. Here, we reviewed the literature to discover the current status in understanding the relationships between NG and DBs in individual proteins. Our results showed that more than 2700 human proteins carry both PTMs, and fewer than 2% of them have been investigated in the associations between NG and DBs. We summarized both these proteins with the reported relationships in the two PTMs and the tools used to discover the relationships. We hope that, by exposing this largely understudied field, more investigations can be encouraged to unveil the hidden relationships of NG and DBs in the majority of membranes and secreted proteins for pathophysiological understanding and biotherapeutic development.

Structure-guided design of antibacterials that allosterically inhibit DNA gyrase.

A series of DNA gyrase inhibitors were designed based on the X-ray structure of a parent thiophene scaffold with the objective to improve biochemical and whole-cell antibacterial activity, while reducing cardiac ion channel activity. The binding mode and overall design hypothesis of one series was confirmed with a co-crystal structure with DNA gyrase. Although some analogs retained both biochemical activity and whole-cell antibacterial activity, we were unable to significantly improve the activity of the series and analogs retained activity against the cardiac ion channels, therefore we stopped optimization efforts.

Novel KV7 ion channel openers for the treatment of epilepsy and implications for detrusor tissue contraction.

Neuronal voltage-gated potassium channels, KV7s, are the molecular mediators of the M current and regulate membrane excitability in the central and peripheral neuronal systems. Herein, we report novel small molecule KV7 openers that demonstrate anti-seizure activities in electroshock and pentylenetetrazol-induced seizure models without influencing Rotarod readouts in mice. The anti-seizure activity was determined to be proportional to the unbound concentration in the brain. KV7 channels are also expressed in the bladder smooth muscle (detrusor) and activation of these channels may cause localized undesired effects. Therefore, the impact of individual KV7 isoforms was investigated in human detrusor tissue using a panel of KV7 openers with distinct activity profiles among KV7 isoforms. KCNQ4 and KCNQ5 mRNA were highly expressed in detrusor tissue, yet a compound that has significantly reduced activity on homomeric KV7.4 did not reduce detrusor contraction. This may suggest that the homomeric KV7.4 channel plays a less significant role in bladder contraction and further investigation is needed.

Discovery and Optimization of 5-Amino-1,2,3-triazole-4-carboxamide Series against Trypanosoma cruzi.

Chagas' disease, caused by the protozoan parasite Trypanosoma cruzi, is the most common cause of cardiac-related deaths in endemic regions of Latin America. There is an urgent need for new safer treatments because current standard therapeutic options, benznidazole and nifurtimox, have significant side effects and are only effective in the acute phase of the infection with limited efficacy in the chronic phase. Phenotypic high content screening against the intracellular parasite in infected VERO cells was used to identify a novel hit series of 5-amino-1,2,3-triazole-4-carboxamides (ATC). Optimization of the ATC series gave improvements in potency, aqueous solubility, and metabolic stability, which combined to give significant improvements in oral exposure. Mitigation of a potential Ames and hERG liability ultimately led to two promising compounds, one of which demonstrated significant suppression of parasite burden in a mouse model of Chagas' disease.

Enhanced effects of isoflurane on the long QT syndrome 1-associated A341V mutant.

BACKGROUND: The impact of volatile anesthetics on patients with inherited long QT syndrome (LQTS) is not well understood. This is further complicated by the different genotypes underlying LQTS. No studies have reported on the direct effects of volatile anesthetics on specific LQTS-associated mutations. We investigated the effects of isoflurane on a common LQTS type 1 mutation, A341V, with an unusually severe phenotype. METHODS: Whole cell potassium currents (IKs) were recorded from HEK293 and HL-1 cells transiently expressing/coexpressing wild-type KCNQ1 (α-subunit), mutant KCNQ1, wild-type KCNE1 (ß-subunit), and fusion KCNQ1 + KCNE1. Current was monitored in the absence and presence of clinically relevant concentration of isoflurane (0.54 ± 0.05 mM, 1.14 vol %). Computer simulations determined the resulting impact on the cardiac action potential. RESULTS: Isoflurane had significantly greater inhibitory effect on A341V + KCNE1 (62.2 ± 3.4%, n = 8) than on wild-type KCNQ1 + KCNE1 (40.7 ± 4.5%; n = 9) in transfected HEK293 cells. Under heterozygous conditions, isoflurane inhibited A341V + KCNQ1 + KCNE1 by 65.2 ± 3.0% (n = 13) and wild-type KCNQ1 + KCNE1 (2:1 ratio) by 32.0 ± 4.5% (n = 11). A341V exerted a dominant negative effect on IKs. Similar differential effects of isoflurane were also observed in experiments using the cardiac HL-1 cells. Mutations of the neighboring F340 residue significantly attenuated the effects of isoflurane, and fusion proteins revealed the modulatory effect of KCNE1. Action potential simulations revealed a stimulation frequency-dependent effect of A341V. CONCLUSIONS: The LQTS-associated A341V mutation rendered the IKs channel more sensitive to the inhibitory effects of isoflurane compared to wild-type IKs in transfected cell lines; F340 is a key residue for anesthetic action.

Utility of frozen cell lines in medium throughput electrophysiology screening of hERG and NaV1.5 blockade.

INTRODUCTION: The development of drug candidates must take into account that many compounds have off-target activity against voltage-gated ion channels (VGIC) which may prevent their progression to market. Of particular concern are hERG and hNa(V)1.5. Screening against these ion channels is necessary but expensive, partially due to maintenance of constantly cultured cell lines. Here, we show that frozen HEK-293 cells can be maintained indefinitely, reducing variability in cell performance, time and expense of cell culture. METHODS: Cells, constantly cultured or frozen, were assayed on the PatchXpress 7000A using tool compounds. RESULTS: Amitriptyline, quinidine, compound A, fluoxetine and imipramine inhibited hERG with IC(50)s (paired values denote constantly cultured and frozen, respectively) of 4.8±0.4 and 5.1±0.4, 1.4±0.1 and 1.1±0.1, 24.4±2.4 and 21.9±1.8, 2.1±0.4 and 2.1±0.1, 5.2±0.4 and 4.0±0.2µM. Quinidine, flecainide, mexiletine and amitriptyline inhibited hNa(V)1.5 with IC(50)s of 46.6±4.3 and 28.0±2.3, 7.6±0.7 and 6.2±0.5, 153.5±13.0 and 106.0±4.7, 5.5±0.5 and 4.8±0.2µM. Voltage dependences of activation (V(1/2)) for hERG were statistically identical, 0.4±0.8mV and 2.5±0.5mV. In hNa(V)1.5, the V(1/2) of inactivation and activation were statistically identical, -82.7±0.1mV versus -84.9±0.3mV, -47.5±0.3mV versus -45.0±0.6mV. Current density in both conditions in hERG experiments was similar, 47.0±4.1pA versus 42.3±6.0pA/pF. DISCUSSION: hERG and hNa(V)1.5 screens run using frozen cells have statistically identical IC(50)s, voltage dependence of activation, IV relationships and current density to screens using continuously cultured cells. Frozen cells have more constant performance and allow rapid switching between experiments on several cell lines without sacrificing data quality.