DBCO-PEG4-Desthiobiotin is a PEG linker containing a desthiobiotin group and a DBCO functional group. Desthiobiotin is used for affinity-based applications such as pull-down assays or for ligating with streptavidin proteins while DBCO is a click chemistry handle that quickly reacts with azide groups on target molecules. Desthiobiotin is a sulfur-free analogue of biotin which binds streptavidin with slightly less strength than biotin, which provides it with a soft-release characteristic that is useful for in pull-down assays by minimizing co-elution with endogenous biotinylated molecules. The inclusion of a PEG linker in this molecule improves its aqueous solubility.