A Caffeic Acid Matrix Improves In Situ Detection and Imaging of Proteins with High Molecular Weight Close
to 200,000 Da in Tissues by Matrix-Assisted Laser Desorption/Ionization
Mass Spectrometry Imaging
posted on 2021-08-18, 15:33authored byHaiqiang Liu, Manman Han, Jinming Li, Liang Qin, Lulu Chen, Qichen Hao, Dongxu Jiang, Difan Chen, Yuanyuan Ji, Hang Han, Chunlin Long, Yijun Zhou, Jinchao Feng, Xiaodong Wang
To our knowledge, this was the first
study in which caffeic acid
(CA) was successfully evaluated as a matrix to enhance the in situ detection and imaging of endogenous proteins in
three biological tissue sections (i.e., a rat brain
and Capparis masaikai and germinating
soybean seeds) by matrix-assisted laser desorption/ionization mass
spectrometry imaging (MALDI-MSI). Our results show several properties
of CA, including strong ultraviolet absorption, a super-wide MS detection
mass range close to 200,000 Da, micrometer-sized matrix crystals,
uniform matrix deposition, and high ionization efficiency. More high-molecular-weight
(HMW) protein ion signals (m/z >
30,000) could be clearly detected in biological tissues with the use
of CA, compared to two commonly used MALDI matrices, i.e., sinapinic acid (SA) and ferulic acid (FA). Notably, CA shows excellent
performance for HMW protein in situ detection from
biological tissues in the mass range m/z > 80,000, compared to the use of SA and FA. Furthermore, the
use
of a CA matrix also significantly enhanced the imaging of proteins
on the surface of selected biological tissue sections. Three HMW protein
ion signals (m/z 50,419, m/z 65,874, and m/z 191,872) from a rat brain, two sweet proteins (mabinlin-2
and mabinlin-4) from a Capparis masaikai seed, and three HMW protein ion signals (m/z 94,838, m/z 134,204,
and m/z 198,738) from a germinating
soybean seed were successfully imaged for the first time. Our study
proves that CA has the potential to become a standard organic acid
matrix for enhanced tissue imaging of HMW proteins by MALDI-MSI in
both animal and plant tissues.