Microwave-assisted synthesis of triple-helical, collagen-mimetic lipopeptides

Microwave-assisted rapid conjugation of horseradish peroxidase-dextran aldehyde with Schiff base reaction and decolorization of Reactive Blue 19

Microwave irradiation has become a routine technique in homogeneous and effective heating in organic synthesis. However, its application in enzyme-containing reactions is limited since it can cause denaturation of the enzyme. In this study, we have briefly investigated the effect of microwave heating on the conjugation reaction of horseradish peroxidase (HRP) with aldehyde derivative of dextran (D-CHO). The reaction was irradiated by microwave at 50 °C for 5 min. The conjugate was confirmed via GPC, in which the conjugates of HRP and D-CHO coexist with free unbound HRP molecules. Activity studies of HRP revealed that there is a small decrease in conjugate activity relative to the free enzyme after a short bioconjugation reaction with microwave irradiation. In decolorization studies of the textile dye Reactive Blue 19 (RB19), 99% of RB19 was decolorized through the free enzyme at 35 °C while the decolorization of the dye was 96% at 25-35 °C by the conjugate, which is a critical result showing clearly that the HRP conjugated via D-CHO is not denatured and still active after microwave-assisted reaction. This phenomenon is due to the multiple point conjugation of D-CHO on the surface of HRP and locking the 3D structure which may prevent changes in the secondary or tertiary structure of the enzyme. The results reveal that microwave irradiation can be used in production of covalently modified enzymes.

Regeneration of aged DMF for use in solid-phase peptide synthesis

Dimethylformamide (DMF), which is still the most commonly used solvent for Fmoc-SPPS, has the potential for degradation over time on exposure to air (and water vapour) and storage, to give dimethylamine and formic acid impurities. In particular, dimethylamine can lead to unwanted deprotection of the fluorenylmethyloxycarbonyl (Fmoc) group during, for example, the initial loading of Fmoc amino acids in SPPS, which leads reduced calculated loading values. We have found that treatment of such aged DMF by simple sparging with an inert gas (N₂ ), or vacuum sonication, can regenerate the DMF in order to restore loading levels back to those found for newer, fresh, DMF samples.

An investigation of the role of the adiponectin variable domain on the stability of the collagen-like domain

The chemical synthesis is described of a polypeptide construct possessing both the variable and the collagen-like domain of adiponectin, which can be used as a model system for probing the influence of the variable domain on multimerization of this important circulating hormone. Using a collagen domain repeat peptide unit derived from native adiponectin or a glutamic acid analogue was ineffective due to noncollagenous conformational properties in both cases. However, employing a collagen model peptide and linking this to the variable domain thioester peptide using native chemical ligation proved effective. The 63 residue peptide was characterized by circular dichroism and mass spectrometry which demonstrated that a collagen-like triple-helical structure was preserved.

Development of a Backbone Cyclic Peptide Library as Potential Antiparasitic Therapeutics Using Microwave Irradiation

Protein-protein interactions (PPIs) are intimately involved in almost all biological processes and are linked to many human diseases. Therefore, there is a major effort to target PPIs in basic research and in the pharmaceutical industry. Protein-protein interfaces are usually large, flat, and often lack pockets, complicating the discovery of small molecules that target such sites. Alternative targeting approaches using antibodies have limitations due to poor oral bioavailability, low cell-permeability, and production inefficiency. Using peptides to target PPI interfaces has several advantages. Peptides have higher conformational flexibility, increased selectivity, and are generally inexpensive. However, peptides have their own limitations including poor stability and inefficiency crossing cell membranes. To overcome such limitations, peptide cyclization can be performed. Cyclization has been demonstrated to improve peptide selectivity, metabolic stability, and bioavailability. However, predicting the bioactive conformation of a cyclic peptide is not trivial. To overcome this challenge, one attractive approach it to screen a focused library to screen in which all backbone cyclic peptides have the same primary sequence, but differ in parameters that influence their conformation, such as ring size and position. We describe a detailed protocol for synthesizing a library of backbone cyclic peptides targeting specific parasite PPIs. Using a rational design approach, we developed peptides derived from the scaffold protein Leishmania receptor for activated C-kinase (LACK). We hypothesized that sequences in LACK that are conserved in parasites, but not in the mammalian host homolog, may represent interaction sites for proteins that are critical for the parasites' viability. The cyclic peptides were synthesized using microwave irradiation to reduce reaction times and increase efficiency. Developing a library of backbone cyclic peptides with different ring sizes facilitates a systematic screen for the most biological active conformation. This method provides a general, fast, and facile way to synthesize cyclic peptides.

Peptide release, side-chain deprotection, work-up, and isolation

After having successfully synthesized a peptide, it has to be released from the solid support, unless it is being used for on-resin display. The linker and, in some cases, the cleavage mixture determine the C-terminal functionality of the released peptide. In most cases, the peptide is released with concomitant removal of side-chain protecting groups. However, some combinations of linkers and side-chain protecting groups enable a two-stage procedure, either using orthogonal chemistry or graduated labilities. Herein, we describe protocols for the release of peptides from the most commonly used linker types providing a variety of different C-terminal functionalities, including acids, amides, amines, and aldehydes. Moreover, suggestions for determination of peptide purity and for storage conditions are provided.

Ultrasound enhanced matrix metalloproteinase-9 triggered release of contents from echogenic liposomes

The extracellular enzyme matrix metalloproteinase-9 (MMP-9) is overexpressed in atherosclerotic plaques and in metastatic cancers. The enzyme is responsible for rupture of the plaques and for the invasion and metastasis of a large number of cancers. The ability of ultrasonic excitation to induce thermal and mechanical effects has been used to release drugs from different carriers. However, the majority of these studies were performed with low frequency ultrasound (LFUS) at kilohertz frequencies. Clinical usage of LFUS excitations will be limited due to harmful biological effects. Herein, we report our results on the release of encapsulated contents from substrate lipopeptide incorporated echogenic liposomes triggered by recombinant human MMP-9. The contents release was further enhanced by the application of diagnostic frequency (3 MHz) ultrasound. The echogenic liposomes were successfully imaged employing a medical ultrasound transducer (4-15 MHz). The conditioned cell culture media from cancer cells (secreting MMP-9) released the encapsulated dye from the liposomes (30-50%), and this release is also increased (50-80%) by applying diagnostic frequency ultrasound (3 MHz) for 3 min. With further developments, these liposomes have the potential to serve as multimodal carriers for triggered release and simultaneous ultrasound imaging.

Synthesis and splice-redirecting activity of branched, arginine-rich peptide dendrimer conjugates of peptide nucleic acid oligonucleotides

Arginine-rich cell-penetrating peptides have found excellent utility in cell and in vivo models for enhancement of delivery of attached charge-neutral PNA or PMO oligonucleotides. We report the synthesis of dendrimeric peptides containing 2- or 4-branched arms each having one or more R-Ahx-R motifs and their disulfide conjugation to a PNA705 splice-redirecting oligonucleotide. Conjugates were assayed in a HeLa pLuc705 cell assay for luciferase up-regulation and splicing redirection. Whereas 8-Arg branched peptide-PNA conjugates showed poor activity compared to a linear (R-Ahx-R)(4)-PNA conjugate, 2-branched and some 4-branched 12 and 16 Arg peptide-PNA conjugates showed activity similar to that of the corresponding linear peptide-PNA conjugates. Many of the 12- and 16-Arg conjugates retained significant activity in the presence of serum. Evidence showed that biological activity in HeLa pLuc705 cells of the PNA conjugates of branched and linear (R-Ahx-R) peptides is associated with an energy-dependent uptake pathway, predominantly clathrin-dependent, but also with some caveolae dependence.

Synthetic collagen mimics: self-assembly of homotrimers, heterotrimers and higher order structures

Collagen is a fascinating system of proteins that undergo a multi-step, hierarchical self-assembly which starts from individual peptide chains that assemble into a canonical triple helix. These triple helices then assemble into higher order structures which are often, but not always, fibrous in nature. While collagen is the most abundant protein in the human body, the details of its structure and mechanism of assembly are surprisingly poorly understood. This critical review will focus on small peptide systems, commonly referred to as collagen mimetic peptides (CMPs) which have been used successfully to help unravel some of the mystery of this complex structure. We will discuss homotrimeric CMPs, which are the most commonly researched subject in this field, and the structure of the collagen triple helix in detail and the factors that contribute to its stabilization. We will also cover how CMPs have been used to study breaks in triple helical domains as models for connective tissue diseases and, finally, how they have been used to understand the interactions of collagenous proteins with cell-surface receptors. Additionally, we will focus on heterotrimeric CMPs, a relatively new area of collagen research. Finally, we will deal with CMPs used as models for higher level self-assembly and also as materials that are designed to mimic the function of collagens in the extracellular matrix (178 references).