Synthesis of Aliphatic Polyanhydrides with Controllable and Reproducible Molecular Weight.

Polyanhydrides have been synthesized for decades by melt-polycondensation of diacid monomers and 5 to >10 times mole excess acetic anhydride to diacid monomers to form polymers with a polydispersity ranging from 2.5 to 6 and low reproducibility. Hydrophobic segments in polyanhydrides are beneficial to hinder the characteristic hydrolytic cleavage of an anhydride bond that provides stable polyanhydrides at room temperature. The objective of this work is to synthesize aliphatic polyanhydrides with various hydrophobic segments, controllable and reproducible molecular weight, and low polydispersity that are essential for potential use as drug carriers. A series of polyanhydrides of suberic, azelaic, sebacic, and dodecanedioic acids with controlled molecular weight, reduced polydispersity, and standard deviation of molecular weights, have been synthesized. All synthesized polyanhydrides were thoroughly characterized by NMR, Fourier transform infrared spectroscopy, and gel permeation chromatography. Molecular weights of the synthesized polyanhydrides are highly controllable, depending on the degree of activation of the dicarboxylic acid monomers, i.e., the amount of acetic anhydride used during synthesis. Polyanhydrides have been synthesized in triplicate by melt-polycondensation, using various mole ratios of acetic anhydride to diacids. The standard deviation of the molecular weights of the polyanhydrides is minute when using 1 equivalent of acetic anhydride during the activation of dicarboxylic acids, whereas if excess acetic anhydride is used, the standard deviation is very high. The effect of safe and natural inorganic catalysts, Calcium oxide, Zinc oxide, and Calcium carbonate on polymerization is also studied. As-synthesized poly(sebacic acid) can offer convenience to use in controlled drug delivery applications. In vitro drug release study using Temozolamide (TMZ), a medication used to treat brain tumors such as glioblastoma and anaplastic astrocytoma, shows 14% TMZ release after the first hour and 70% release over one day from the poly(sebacic acid) wafers.

Characterization and Evaluation of Injectable Biodegradable Polymer Multimodality Radiologic Markers in an In Vivo Murine Model.

Biodegradable polymer clips as multidimensional soft tissue biopsy markers were developed with better biocompatibility and imaging features. Unlike the commercially available metallic biopsy markers, the developed polymer clips are temporary implants with similar efficacies as metal markers in imaging and detection and get absorbed within the body with time. Herein, we evaluate the degradation rate of three resorbable polymer-based marker compounds in an in vivo murine model. Three polymers, abbreviated as Polymer A (PLGA poly(lactic-co-glycolic acid)50:50), Polymer B (PLGA (poly(lactic-co-glycolic acid)) 75:25), and Polymer C (polycaprolactone (PCL)), mixed with 20% lipiodol and 0.2% iron oxide and a control polymer were implanted into nine mice, followed by CT and MRI imaging. Images were evaluated for conspicuity. Specimens were examined for tissue analysis of iodine and iron contents. Significant differences in polymer resorption and visualization on CT were noted, particularly at 8 weeks (p < 0.027). Polymers A, B, and C were visible by CT at 4, 6, and 8 weeks, respectively. All marker locations were detected on MRI (T1 and SWI) after 24 weeks, with tattooing of the surrounding soft tissue by iron deposits. CT and MR visible polymer markers can be constructed to possess variable resorption, with stability ranging between 4 and 14 weeks post placement, making this approach suitable for distinct clinical scenarios with varying time points.

Seven Post-synthetic Covalent Reactions in Tandem Leading to Enzyme-like Complexity within Metal-Organic Framework Crystals.

The design of enzyme-like complexity within metal-organic frameworks (MOFs) requires multiple reactions to be performed on a MOF crystal without losing access to its interior. Here, we show that seven post-synthetic reactions can be successfully achieved within the pores of a multivariate MOF, MTV-IRMOF-74-III, to covalently incorporate tripeptides that resemble the active sites of enzymes in their spatial arrangement and compositional heterogeneity. These reactions build up H2N-Pro-Gly-Ala-CONHL and H2N-Cys-His-Asp-CONHL (where L = organic struts) amino acid sequences by covalently attaching them to the organic struts in the MOFs, without losing porosity or crystallinity. An enabling feature of this chemistry is that the primary amine functionality (-CH2NHBoc) of the original MOF is more reactive than the commonly examined aromatic amines (-NH2), and this allowed for the multi-step reactions to be carried out in tandem within the MOF. Preliminary findings indicate that the complexity thus achieved can affect reactions that were previously accomplished only in the presence of enzymes.

L-Aspartate links for stable sodium metal-organic frameworks.

Metal-organic frameworks (MOFs) based purely on sodium are rare, typically due to large numbers of coordinating solvent ligands. We designed a tetratopic aspartate-based linker with flexible carboxylate groups to enhance framework stability. We report two new air-stable sodium MOFs, MOF-705 and MOF-706, comprising 2D sodium oxide sheets.

Extended ubiquitin species are protein-based DUB inhibitors.

A frameshift mutation in the transcript of the ubiquitin-B gene leads to a C-terminally extended ubiquitin (Ub), UBB(+1). UBB(+1) has been considered to inhibit proteasomes and as such to be the underlying cause for toxic protein buildup correlated with certain neuropathological conditions. We demonstrate that expression of extended Ub variants leads to accumulation of heterogeneously linked polyubiquitin conjugates, indicating a pervasive effect on Ub-dependent turnover. 20S proteasomes selectively proteolyzed Ub extensions, yet no evidence for inhibition of 26S holoenzymes was found. However, among susceptible targets for inhibition was Ubp6, the primary enzyme responsible for disassembly of Lys48 linkages at 26S proteasomes. Processing of Lys48 and Lys63 linkages by other deubiquitinating enzymes (DUBs) was also inhibited. Disruption of Ub-dependent degradation by extended Ub variants may therefore be attributed to their inhibitory effect on select DUBs, thus shifting research efforts related to protein accumulation in neurodegenerative processes from proteasomes to DUBs.

Systematic identification of proteins binding to chromatin-embedded ubiquitylated H2B reveals recruitment of SWI/SNF to regulate transcription.

Chromatin posttranslational modifications (PTMs), including monoubiquitylation of histone H2B on lysine 120 (H2Bub1), play a major role in regulating genome functions. To elucidate the molecular mechanisms of H2Bub1 activity, a chromatin template uniformly containing H2Bub1 was used as an affinity matrix to identify preferentially interacting human proteins. Over 90 such factors were found, including proteins and protein complexes associated with transcription, RNA posttranscriptional modifications, and DNA replication and repair. Notably, we found that the SWI/SNF chromatin remodeling complex associates preferentially with H2Bub1-rich chromatin. Moreover, SWI/SNF is required for optimal transcription of a subset of genes that are selectively dependent on H2Bub1. Our findings substantially expand the known H2Bub1 interactome and provide insights into the functions of this PTM in mammalian gene regulation.

Chemical and semisynthesis of posttranslationally modified proteins.

Posttranslational modifications of proteins play crucial roles in health and disease by affecting numerous aspects of protein structure, function, stability and sub cellular localization. Yet understanding the effects of these modifications on several of these processes at the molecular level has been hindered by the lack of homogeneously modified proteins obtained via traditional biochemical and molecular biology approaches. Moreover, the preparation of such bioconjugates at a workable level is highly demanding. Recent advances in protein chemistry applying chemical and semisynthetic approaches are becoming increasingly beneficial to overcome these challenges. These methods allow site-specific modifications of a desired protein and afford the product in large quantities for biochemical and structural analyses. In this review, we survey these efforts and their importance in dissecting the role of several posttranslational modifications in various proteins. Several examples are presented where glycosylated, phosphorylated, ubiquitinated, lipidated, acetylated and methylated proteins were prepared.

Native chemical ligation at glutamine.

The desulfurization reaction introduced by Yan and Dawson as a postnative chemical ligation step greatly expanded the scope of ligation chemistry beyond Xaa-Cys (Xaa is any amino acid) by making ligation at Xaa-Phe, Xaa-Val, Xaa-Lys, Xaa-Leu, Xaa-Thr, and Xaa-Pro junctions accessible in the synthesis of functional proteins. A new ligation site based on Xaa-Gln utilizing γ-mercaptoglutamine is reported, and several examples on the efficiency of ligation coupled with desulfurization are provided.

Chemical synthesis and expression of the HIV-1 Rev protein.

The HIV-1 Rev protein is responsible for shuttling partially spliced and unspliced viral mRNA out of the nucleus. This is a crucial step in the HIV-1 lifecycle, thus making Rev an attractive target for the design of anti-HIV drugs. Despite its importance, there is a lack of structural, biophysical, and quantitative information about Rev. This is mainly because of its tendency to undergo self-assembly and aggregation; this makes it very difficult to express and handle. To address this knowledge gap, we have developed two new highly efficient and reproducible methods to prepare Rev in large quantities for biochemical and structural studies: 1) Chemical synthesis by using native chemical ligation coupled with desulfurization. Notably, we have optimized our synthesis to allow for a one-pot approach for the ligation and desulfurization steps; this reduced the number of purification steps and enabled the obtaining of desired protein in excellent yield. Several challenges emerged during the design of this Rev synthesis, such as racemization, reduced solubility, formylation during thioester synthesis, and the necessity for using orthogonal protection during desulfurization; solutions to these problems were found. 2) A new method for expression and purification by using a vector that contained an HLT tag, followed by purification with a Ni column, a cation exchange column, and gel filtration. Both methods yielded highly pure and folded Rev. The CD spectra of the synthetic and recombinant Rev proteins were identical, and consistent with a predominantly helical structure. These advances should facilitate future studies that aim at a better understanding of the structure and function of the protein.