Can electromagnetic fields influence the structure and enzymatic digest of proteins? A critical evaluation of microwave-assisted proteomics protocols.
This study reevaluates the putative advantages of microwave-assisted tryptic digests compared to conventionally heated protocols performed at the same temperature. An initial investigation of enzyme stability in a temperature range of 37-80 °C demonstrated that trypsin activity declines sharply at temperatures above 60 °C, regardless if microwave dielectric heating or conventional heating is employed. Tryptic digests of three proteins of different size (bovine serum albumin, cytochrome c and β-casein) were thus performed at 37 °C and 50 °C using both microwave and conventional heating applying accurate internal fiber-optic probe reaction temperature measurements. The impact of the heating method on protein degradation and peptide fragment generation was analyzed by SDS-PAGE and MALDI-TOF-MS. Time-dependent tryptic digestion of the three proteins and subsequent analysis of the corresponding cleavage products by MALDI-TOF provided virtually identical results for both microwave and conventional heating. In addition, the impact of electromagnetic field strength on the tertiary structure of trypsin and BSA was evaluated by molecular mechanics calculations. These simulations revealed that the applied field in a typical laboratory microwave reactor is 3-4 orders of magnitude too low to induce conformational changes in proteins or enzymes.
Christian Doppler Laboratory for Microwave Chemistry (CDLMC) and Institute of Chemistry, Karl-Franzens-University Graz, Heinrichstrasse 28/I, A-8010 Graz, Austria.
Markus
M
Damm
Christoph
C
Nusshold
David
D
Cantillo
Gerald N
GN
Rechberger
Karl
K
Gruber
Wolfgang
W
Sattler
C Oliver
CO
Kappe
D002364:Caseins / Q000737:chemistry*; D003198:Computer Simulation; D045304:Cytochromes c / Q000737:chemistry*; D004574:Electromagnetic Fields; D004591:Electrophoresis, Polyacrylamide Gel; D004795:Enzyme Stability; D006361:Heating; D006358:Hot Temperature; D008872:Microwaves; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry; D011487:Protein Conformation; D040901:Proteomics / Q000379:methods*; D012710:Serum Albumin, Bovine / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014357:Trypsin / Q000378:metabolism
D002364:Caseins; D010446:Peptide Fragments; D012710:Serum Albumin, Bovine; D045304:Cytochromes c; D014357:Trypsin