title: Rational selection of the optimum MALDI matrix for top-down proteomics by in-source decay.
abstract: In-source decay (ISD) in MALDI leads to c- and z-fragment ion series enhanced by hydrogen radical donors and is a useful method for sequencing purified peptides and proteins. Until now, most efforts to improve methods using ISD concerned instrumental optimization. The most widely used ISD matrix is 2,5-dihydroxybenzoic acid (DHB). We present here a rational way to select MALDI matrixes likely to enhance ISD for top-down proteomic approaches. Starting from Takayama's model (Takayama, M. J. Am. Soc. Mass Spectrom. 2001, 12, 1044-9), according to which formation of ISD fragments (c and z) would be due to a transfer of hydrogen radical from the matrix to the analyte, we evaluated the hydrogen-donating capacities of matrixes, and thus their ISD abilities, with spirooxazines (hydrogen scavengers). The determined hydrogen-donating abilities of the matrixes are ranked as follows: picolinic acid (PA) > 1,5-diaminonaphtalene (1,5-DAN) > DHB > sinapinic acid > alpha-cyano-4-hydroxycinnamic acid. The ISD enhancement obtained by using 1,5-DAN compared to DHB was confirmed with peptides and proteins. On that basis, a matrix-enhanced ISD approach was successfully applied to sequence peptides and proteins up to approximately 8 kDa. Although PA alone is not suitable for peptide and protein ionization, ISD signals could be further enhanced when PA was used as an additive to 1,5-DAN. The optimized matrix preparation was successfully applied to identify larger proteins by large ISD tag researches in protein databases (BLASTp). Coupled with an adequate separation method, ISD is a promising tool to include in a top-down proteomic strategy.
authors.affiliation: Laboratoire de Spectrométrie de Masse, CART/GIGA-R, Institut de Chimie, Bat. B6c, Université de Liège, Liège B-4000, Belgium. e.depauw@ulg.ac.be
authors.forename: Kevin
authors.initials: K
authors.lastname: Demeure
authors.forename: Loïc
authors.initials: L
authors.lastname: Quinton
authors.forename: Valérie
authors.initials: V
authors.lastname: Gabelica
authors.forename: Edwin
authors.initials: E
authors.lastname: De Pauw
mesh_terms: D006859:Hydrogen / Q000737:chemistry; D007328:Insulin / Q000737:chemistry; D015394:Molecular Structure; D009281:Naphthalenes; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry; D010848:Picolinic Acids; D040901:Proteomics / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
chemical_list: D007328:Insulin; D009281:Naphthalenes; D010455:Peptides; D010848:Picolinic Acids; C031721:naphthalene; D006859:Hydrogen; C030614:picolinic acid