Modulation of protein aggregation by polyethylene glycol conjugation: GCSF as a case study.

Polyethylene glycol (PEG) conjugation to proteins has emerged as an important technology to produce drug molecules with sustained duration in the body. However, the implications of PEG conjugation to protein aggregation have not been well understood. In this study, conducted under physiological pH and temperature, N-terminal attachment of a 20 kDa PEG moiety to GCSF had the ability to (1) prevent protein precipitation by rendering the aggregates soluble, and (2) slow the rate of aggregation relative to GCSF.

DNA-protein cross-linking via guanine oxidation: dependence upon protein and photosensitizer.

DNA-protein cross-links form when guanine undergoes a 1-electron oxidation in a flash-quench experiment, and the importance of reactive oxygen species, protein, and photosensitizer is examined here. In these experiments, a strong oxidant produced by oxidative quenching of a DNA-bound photosensitizer generates an oxidized guanine base that reacts with protein to form the covalent adduct. These cross-links are cleaved by hot piperidine and are not the result of reactive oxygen species, since neither a hydroxyl radical scavenger (mannitol) nor oxygen affects the yield of DNA-histone cross-linking, as determined via a chloroform extraction assay.

DNA cross-linking with metallointercalator-peptide conjugates.

Short peptides have been tethered to a DNA-intercalating ruthenium complex to create a photoactivated cross-linking reagent. The ruthenium complex, [Ru(phen)(bpy')(dppz)]2+ (phen = 1,10-phenanthroline, bpy' = 4-(butyric acid)-4'-methyl-2,2'-bipyridine, and dppz = dipyridophenazine), delivers the peptide to DNA and initiates the cross-linking reaction by oxidizing DNA upon irradiation in the presence of an oxidative quencher. The tethered peptide, only five to six residues in length, forms cross-links with the oxidized site in DNA.