title: Improving protein array performance: focus on washing and storage conditions.
abstract: For protein microarrays, maintaining protein stability during the slide processing steps of washing, drying, and storage is of major concern. Although several studies have focused on the stability of immobilized antibodies in antibody microarrays, studies on protein-protein interaction arrays and enzyme arrays are lacking. In this paper we used five bait-prey protein interaction pairs and three enzymes to optimize the washing, drying, and storage conditions for protein arrays. The protein arrays for the study were fabricated by combining HaloTag technology and cell-free protein expression. The HaloTag technology, in combination with cell-free expression, allowed rapid expression and immobilization of fusion proteins on hydrogel-coated glass slides directly from cell extracts without any prior purification. Experimental results indicate enzyme captured on glass slides undergoes significant loss of activity when washed and spin-dried using only phosphate buffer, as is typically done with antibody arrays. The impact of washing and spin-drying in phosphate buffer on protein-protein interaction arrays was minimal. However, addition of 5% glycerol to the wash buffer helps retain enzyme activity during washing and drying. We observed significant loss of enzyme activity when slides were stored dry at 4 degrees C, however immobilized enzymes remained active for 30 days when stored at -20 degrees C in 50% glycerol. We also found that cell-free extract containing HaloTag-fused enzymes could undergo multiple freeze/thaw cycles without any adverse impact on enzyme activity. The findings indicate that for large ongoing studies, proteins of interest expressed in cell-free extract can be stored at -70 degrees C and repeatedly used to print small batches of protein array slides to be used over a few weeks.
authors.affiliation: Research and Development, Promega Corporation, Madison, Wisconsin 53711, USA. nidhi.nath@promega.com
authors.forename: Nidhi
authors.initials: N
authors.lastname: Nath
authors.forename: Robin
authors.initials: R
authors.lastname: Hurst
authors.forename: Brad
authors.initials: B
authors.lastname: Hook
authors.forename: Poncho
authors.initials: P
authors.lastname: Meisenheimer
authors.forename: Kate Q
authors.initials: KQ
authors.lastname: Zhao
authors.forename: Nadine
authors.initials: N
authors.lastname: Nassif
authors.forename: Robert F
authors.initials: RF
authors.lastname: Bulleit
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Storts
mesh_terms: D002474:Cell-Free System; D017868:Cyclic AMP-Dependent Protein Kinases / Q000032:analysis / Q000235:genetics; D004795:Enzyme Stability; D040081:Protein Array Analysis / Q000295:instrumentation / Q000379:methods*; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000032:analysis* / Q000235:genetics; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics; D001618:beta-Lactamases / Q000032:analysis / Q000235:genetics
chemical_list: D011993:Recombinant Fusion Proteins; D017868:Cyclic AMP-Dependent Protein Kinases; D001616:beta-Galactosidase; D001618:beta-Lactamases