title: Quantitative submonolayer spatial mapping of Arg-Gly-Asp-containing peptide organomercaptan gradients on gold with matrix-assisted laser desorption/ionization mass spectrometry.
abstract: Peptides containing the tripeptide sequence Arg-Gly-Asp (RGD) have the ability to bind to members of the integrin superfamily of cell-surface receptors and direct cellular adhesion and haptotaxis. The goal of this work is the development of a rapid and effective method for the quantitative submonolayer spatial composition mapping of surfaces displaying molecular assemblies of RGD-containing organomercaptan peptides on a Au surface using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-MS). Quantitation of the RGD peptide is achieved by determining the peak intensity of the protonated molecular ion, (M + H)+, relative to the (M + H)+ peak for an internal standard, which is similar chemically but with glutamic acid (E) substituted for aspartic acid (D). Using optimized sample preparation procedures, a bilinear calibration was obtained between the quantitative peak intensity ratio and the mole fraction of the RGD-containing peptide. Quantitative compositions were determined with relative standard deviations of <10%, even in the presence of 10x spot-to-spot variations in the absolute signal intensities, by using this internal standard approach. This MALDI-MS quantitative analysis method was employed to probe variable-width two-component counterpropagating electrochemically generated gradients of the two peptides, prepared by coupling in-plane electrochemical potential gradients with the electrosorption reactions of organothiols to vary the composition laterally. The measured lateral composition profiles match the quasi-linear potential gradient model and yield profiles that overlap to a high degree of fidelity in potential space. Thus, MALDI-MS spatial composition mapping should become a powerful tool for the preparation of designed surfaces facilitating the study of cellular adhesion and motility and cell-cell interactions.
authors.affiliation: Department of Chemistry and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Jakubowski
authors.forename: Jonathan V
authors.initials: JV
authors.lastname: Sweedler
authors.forename: Paul W
authors.initials: PW
authors.lastname: Bohn
mesh_terms: D006046:Gold / Q000032:analysis* / Q000737:chemistry; D009842:Oligopeptides / Q000032:analysis* / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D013438:Sulfhydryl Compounds / Q000032:analysis* / Q000737:chemistry
chemical_list: D009842:Oligopeptides; D013438:Sulfhydryl Compounds; D006046:Gold; C047981:arginyl-glycyl-aspartic acid