TABLE 2.

Types of protein posttranslational modifications (PTMs), such as reactive agents, target amino acids, and resulting adducts, and methods used for PTM detection.

PTM type	Agent	Target amino acid	Detection method (references)
Phosphorylation	ATP (γ-phosphate group)	Ser, Thr, Tyr; His	ProQ Diamond gel staining ZrO2/TiO2 based enrichment, TMT labeling
Glycosylation	NDP-monosaccharide (e.g., GDP-mannose, UDP-glucose)	N-glycosylation: Asn in Asn-X-Ser/Thr motif (X represents any amino acid except Pro) O-glycosylation: Ser, Thr	Concanavalin A lectin blot
Acylation Short-chain acids: acetylation, propionylation, succinylation, malonylation, crotonylation) Long-chain acids: palmitoylation, myristoylation	Activated acyl (acyl-CoA)	Lys (ε-amino group)	Anti-acyl-lysine antibody (immunoblots, immune affinity enrichment of acylated proteins prior to LC-MS/MS)
Methylation	S-adenosylmethionine (SAM)	Arg; Lys (ε-amino group)	ADMA- and SDMA-, anti-methyl antibodies (immune affinity enrichment LC-MS/MS) (Carlson and Gozani, 2014)
Peptide conjugation
S-glutathionylation	S-glutathione	Cys (thiol group)	Anti-S-glutathione antibody precipitation; biotin-GSH labeling
Ubiquitination	Ubiquitin (diglycine motif at C-terminus)	Lys (ε-amino group)	Anti-ubiquitin specific antibody (immunoblot)
Sumoylation	SUMO (diglycine motif at C-terminus)	Lys (ε-amino group)	Immunoprecipitation with anti-SUMO-1/2/3 antibodies (Sarge and Park-Sarge, 2009)
RMS related PTMs
Glycation	Active mono- (acrolein) and dicarbonyls (glyoxal, methylglyoxal, reducing sugars)	Lys, Arg (amino group)	Oxyblot kit (carbonyl derivatization to difenylhydrazones and their detection by specific antibody)
S-nitrosylation O-nitrosylation	NO (GSNO), ONOO-, NO2	Cys Tyr	Biotin-switch (immunoblot) (Jaffrey and Snyder, 2001)
Oxidation (ROS)	O2-, H2O2, OH, 1O2	Arg, Lys, Pro, Thr
Sulfurylation (RSS; persulfidation)	H2S	Cys (thiol group)	Tag-switch LC-MS/MS

ADMA, asymmetric dimethylated arginine; SDMA, symmetric dimethylated arginine.