The natural product withaferin A (WFA) exhibits antitumor and antiangiogenesis activity in vivo, which results from this drug's potent growth inhibitory activities. Here, we show that WFA binds to the intermediate filament (IF) protein, vimentin, by covalently modifying its cysteine residue, which is present in the highly conserved alpha-helical coiled coil 2B domain. WFA induces vimentin filaments to aggregate in vitro, an activity manifested in vivo as punctate cytoplasmic aggregates that colocalize vimentin and F-actin. WFA's potent dominant-negative effect on F-actin requires vimentin expression and induces apoptosis. Finally, we show that WFA-induced inhibition of capillary growth in a mouse model of corneal neovascularization is compromised in vimentin-deficient mice. These findings identify WFA as a chemical genetic probe of IF functions, and illuminate a potential molecular target for withanolide-based therapeutics for treating angioproliferative and malignant diseases.

HIV-1 Tat protein plays a crucial role in perturbations of the dopamine (DA) system. Our previous studies have demonstrated that Tat decreases DA uptake, and allosterically modulates DA transporter (DAT) function. In the present study, we have found that Tat interacts directly with DAT, leading to inhibition of DAT function. Through computational modeling and simulations, a potential recognition binding site of human DAT (hDAT) for Tat was predicted. Mutation of tyrosine470 (Y470H) attenuated Tat-induced inhibition of DA transport, implicating the functional relevance of this residue for Tat binding to hDAT. Y470H reduced the maximal velocity of [3H]DA uptake without changes in the Km and IC50 values for DA inhibition of DA uptake but increased DA uptake potency for cocaine and GBR12909, suggesting that this residue does not overlap with the binding sites in hDAT for substrate but is critical for these inhibitors. Furthermore, Y470H also led to transporter conformational transitions by affecting zinc modulation of DA uptake and WIN35,428 binding as well as enhancing basal DA efflux. Collectively, these findings demonstrate Tyr470 as a functional recognition residue in hDAT for Tat-induced inhibition of DA transport and transporter conformational transitions. The consequence of mutation at this residue is to block the functional binding of Tat to hDAT without affecting physiological DA transport.

HIV-1 transactivator of transcription (Tat) protein disrupts the dopamine (DA) neurotransmission by inhibiting DA transporter (DAT) function, leading to increased neurocognitive impairment in HIV-1 infected individuals. Through integrated computational modeling and pharmacological studies, we have demonstrated that mutation of tyrosine470 (Y470H) of human DAT (hDAT) attenuates Tat-induced inhibition of DA uptake by changing the transporter conformational transitions. The present study examined the functional influences of other substitutions at tyrosine470 (Y470F and Y470A) and tyrosine88 (Y88F) and lysine92 (K92M), two other relevant residues for Tat binding to hDAT, in Tat-induced inhibitory effects on DA transport. Y88F, K92M and Y470A attenuated Tat-induced inhibition of DA transport, implicating the functional relevance of these residues for Tat binding to hDAT. Compared to wild type hDAT, Y470A and K92M but not Y88F reduced the maximal velocity of [3H]DA uptake without changes in the Km. Y88F and K92M enhanced IC50 values for DA inhibition of [3H]DA uptake and [3H]WIN35,428 binding but decreased IC50 for cocaine and GBR12909 inhibition of [3H]DA uptake, suggesting that these residues are critical for substrate and these inhibitors. Y470F, Y470A, Y88F and K92M attenuated zinc-induced increase of [3H]WIN35,428 binding. Moreover, only Y470A and K92M enhanced DA efflux relative to wild type hDAT, suggesting mutations of these residues differentially modulate transporter conformational transitions. These results demonstrate Tyr88 and Lys92 along with Tyr470 as functional recognition residues in hDAT for Tat-induced inhibition of DA transport and provide mechanistic insights into identifying target residues on the DAT for Tat binding.

Gliosis is a biological process that occurs during injury repair in the central nervous system and is characterized by the overexpression of the intermediate filaments (IFs) glial fibrillary acidic protein (GFAP) and vimentin. A common thread in manyThe overexpression of glial fibrillary acidic protein (GFAP) 2 with vimentin is a hallmark of reactive gliosis in the central nervous system (CNS) (1, 2). These intermediate filaments (IFs) are expressed by reactive astrocytes and macro-and microglia during traumatic and inflammatory injury and in a range of CNS degenerative diseases (2). In fact, an enigma of major retinal diseases, including age-related macular degeneration, glaucoma, diabetic retinopathy, and retinopathy of prematurity, is retinal gliosis, for which there is no available clinical treatment (3-5).Important fundamental insights on the structural and mechanical functions of IFs (6, 7) have now been validated in mouse lines deficient in type III IFs (2). These studies have illuminated that, whereas overexpression of vimentin and GFAP during CNS stress response and injury repair contributes to scar formation (8), their deficiency can be protective of tissue functions in certain contexts. For instance, pathogenic angiogenesis is impaired in vimentin-deficient (Vim KO) mice due to the decreased ability of newly formed blood vessels to cross the retinal inner limiting membrane in the model of hypoxia-induced retinal neovascularization (9). Interestingly, that study also identified in vimentin and GFAP double deficient (Vim GFAP dKO) mice, and to a lesser extent in Vim KO mice, that the retinal ganglion layer is highly sensitive to mechanical stress, which was not observed in GFAP KO mice. Pathological neovascularization was also reduced in Vim KO mice in the corneal alkali injury model (10) and delayed vascularization in skin injury model (11), which is attributed to defective vascular endothelial cell integrity (12), because vimentin is the sole type III IF expressed in endothelial cells (13). On the other hand, Vim GFAP dKO mice subjected to spinal cord or brain injury recover favorably with improvement of glial scars (14). In fact, the complete absence of type III IFs in Vim GFAP dKO mice helps promote axonal regeneration and regain ambulatory function after spinal cord injury (15). These Vim GFAP dKO

Accurate prediction of absolute protein−ligand binding free energy could considerably enhance the success rate of structure-based drug design but is extremely challenging and time-consuming. Free energy perturbation (FEP) has been proven reliable but is limited to prediction of relative binding free energies of similar ligands (with only minor structural differences) in binding with a same drug target in practical drug design applications. Herein, a Gaussian algorithm-enhanced FEP (GA-FEP) protocol has been developed to enhance the FEP simulation performance, enabling to efficiently carry out the FEP simulations on vanishing the whole ligand and, thus, predict the absolute binding free energies (ABFEs). Using the GA-FEP protocol, the FEP simulations for the ABFE calculation (denoted as GA-FEP/ABFE) can achieve a satisfactory accuracy for both structurally similar and diverse ligands in a dataset of more than 100 receptor− ligand systems. Further, our GA-FEP/ABFE-guided lead optimization against phosphodiesterase-10 led to the discovery of a subnanomolar inhibitor (IC 50 = 0.87 nM, ∼2000-fold improvement in potency) with cocrystal confirmation.