A ruthenium(II) complex supported by trithiacyclononane and aromatic diimine ligand as luminescent switch-on probe for biomolecule detection and protein staining

Platinum Stabilises a Molten-Globule Conformation of a Small Globular Cytosolic Protein SUMO1

Proteins are generally resistant to large conformational changes under physiological conditions. Here, we show that platinum (Pt(II)), which is widely-used metal centre in cancer therapeutic drugs, binds to a cytosolic protein, small ubiquitin-like modifier 1 (SUMO1), under physiological conditions and changes its conformation to a molten globule (MG). Mass spectrometry (ICP-MS) studies confirmed stoichiometric Pt(II) binding to SUMO1. Fluorescence spectroscopy showed Tyr fluorescence quenching and increased ANS binding. Fluorescence assays on Trp-mutants indicated conformational changes and circular dichroism (CD) suggested MG formation upon Pt(II) binding. In contrast, structural homologues of SUMO1 (ubiquitin (Ubq) and SUMO2) showed no conformational changes on Pt(II) titration. Further studies compared the impact of distinct His residues in SUMO1 on Pt(II) binding and protein structure to SUMO2 and Ubq. Experiments at low pH (5.0) implicated His residues interacting with Pt(II), corroborated by the absence of conformational change in the H75L mutant of SUMO1. Pt(II)-His binding in SUMO1 unravels key molecular determinants of Pt(II)-protein interactions and their conformational consequences. SUMO1 with other SUMOylation components are shown to have enhanced expression in several cancers, hence, our study suggests a possible fate of the non-targetability of Pt(II)-based drugs on SUMOylation in cancer cells, upon interaction with SUMO1.

Chemical Conjugation to Less Targeted Proteinogenic Amino Acids

Protein bioconjugates are in high demand for applications in biomedicine, diagnostics, chemical biology and bionanotechnology. Proteins are large and sensitive molecules containing multiple different functional groups and in particular nucleophilic groups. In bioconjugation reactions it can therefore be challenging to obtain a homogeneous product in high yield. Numerous strategies for protein conjugation have been developed, of which a vast majority target lysine, cysteine and to a lesser extend tyrosine. Likewise, several methods that involve recombinantly engineered protein tags have been reported. In recent years a number of methods have emerged for chemical bioconjugation to other amino acids and in this review, we present the progress in this area.

Dextranol: An inert xeroprotectant

Dextranol, a reduced dextran, prevents damage to stored dry protein samples that unmodified dextran would otherwise cause. Desiccation protectants (xeroprotectants) like the polysaccharide dextran are critical for preserving dried protein samples by forming a rigid glass that protects entrapped protein molecules. Stably dried proteins are important for maintaining critical information in clinical samples like blood serum as well as maintaining activity of biologic drug compounds. However, we found that dextran reacts with both dried serum proteins and lyophilized purified proteins during storage, producing high-molecular weight Amadori-product conjugates. These conjugates appeared in a matter of days or weeks when stored at elevated temperatures (37° or 45°C), but also appeared on a timescale of months when stored at room temperature. We synthesized a less reactive dextranol by reducing dextran's anomeric carbon from an aldehyde to an alcohol. Serum samples dried in a dextranol-based matrix protected the serum proteins from forming high-molecular weight conjugates. The levels of four cancer-related serum biomarkers (prostate specific antigen, neuropilin-1, osteopontin, and matrix-metalloproteinase 7) decreased, as measured by immunoassay, when serum samples were stored for one to two weeks in dextran-based matrix. Switching to a dextranol-based xeroprotection matrix slightly reduced the damage to osteopontin and completely stopped any detectable damage during storage in the other three biomarkers when stored for a period of two weeks at 45°C. We also found that switching from dextran to dextranol in a lyophilization formulation eliminates this unwanted reaction, even at elevated temperatures. Dextranol offers a small and easy modification to dextran that significantly improves the molecule's function as a xeroprotectant by eliminating the potential for damaging protein-polysaccharide conjugation.

Luminescent protein staining with Re(i) tetrazolato complexes

Re(i) tricarbonyl diiimine complexes for the first time exploited as luminescent staining agents for SDS-PAGE.

Protein staining agents from low toxic platinum(ii) complexes with bidentate ligands

Low toxic platinum(ii) complexes with bidentate ligands have been developed as novel protein staining agents.