Smart proteolysis samplers for pre‐lab bottom‐up protein analysis – Performance of on‐paper digestion compared to conventional digestion

Here the relation between digestion of proteins by trypsin covalently bound to paper and trypsin in‐solution is investigated. The trypsin acting on paper is covalently bound. A trypsin concentration of 0.5% (w/v) results in the highest digestion activity of all concentrations tested. Additionally, it can be seen that trypsin on‐paper has retained approx. 50% of its activity. Unlike trypsin in‐solution, the stability of the smart proteolysis samplers was regarded to be stable for at least four months when kept refrigerated. Autolysis was very small for covalently bound trypsin: less than 2% compared to in‐solution trypsin. Proteomic analysis of diluted human serum showed more protein identifications (214) in‐solution digestions than on‐paper digestions (76). Also, higher coverage for the in‐solution digestion was obtained. Those proteins identified after on‐paper digestion with no or few disulfide bonds seem to have more similar sequence coverages compared to those identified after in‐solution digestion. Smart samplers allow the determination of at least 70–75 proteins without performing the overnight digestion. All in all, trypsin covalently bound to paper shows to retain high proteolytic activity and is a stable alternative for conventional digestions. In this way, smart proteolytic samplers show their feasibility in pre‐lab sample preparation.