In Situ Characterization of Proteins Using Laserspray Ionization on a High-Performance MALDI-LTQ-Orbitrap Mass Spectrometer
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The MALDI-LTQ-Orbitrap XL mass spectrometer is a high performance instrument capable of high resolution and accurate mass (HRAM) measurements. The maximum m/z of 4000 precludes the MALDI analysis of proteins without generating multiply charged ions. Herein, we present the study of HRAM laserspray ionization mass spectrometry (MS) with MS/MS and MS imaging capabilities using 2-nitrophloroglucinol (2-NPG) as matrix on a MALDI-LTQ-Orbitrap XL mass spectrometer. The optimized conditions for multiply charged ion production have been determined and applied to tissue profiling and imaging. Biomolecules as large as 15 kDa have been detected with up to five positive charges at 100 K mass resolution (at m/z 400). More importantly, MS/MS and protein identification on multiply charged precursor ions from both standards and tissue samples have been achieved for the first time with an intermediate-pressure source. The initial results reported in this study highlight potential utilities of laserspray ionization MS analysis for simultaneous in situ protein identification, visualization, and characterization from complex tissue samples on a commercially available HRAM MALDI MS system.
Key wordsHigh resolution accurate mass (HRAM) analysis Multiply charged MALDI Laserspray ionization In situ protein analysis Mass spectrometric imaging
The authors thank Dr. Robert Thorne’s laboratory at UW-Madison for providing rat brain tissue samples and Dr. Sarah Trimpin at the Wayne State University for helpful suggestions. This work is supported in part by the National Institutes of Health grants (1R01DK071801, 1R56DK071801). The authors acknowledge NIH shared instrument program for funding the instrument purchase (S10 RR029531). C.B.L. acknowledges a NIH-supported Chemistry Biology Interface Training Program Predoctoral Fellowship (grant number T32-GM008505) and an NSF Graduate Research Fellowship (DGE-1256259). L.L. acknowledges an H. I. Romnes Faculty Research Fellowship.
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