TABLE 1. KINASES WITH KNOWN G-LOOP POST-TRANSLATIONAL MODIFICATIONS.

PROTEIN KINASE	PTM at or adjacent to the G- loop	Frequency with which the PTM has been identified	References	Comments
AGC Kinases
PKA	TL GTGSFG	6	22, 48–51
	TL GTGSFG	2	52
	TL GTGSFG	5	22, 48, 49, 53, 54
PKCs
PKCα	GKGSFG K	2	55
	GKGSFG K	1		O-GlcNAcylation
	GKGSFG K	1	56	Ubiquitination
PKCβ	GKGSFG K	1	23	O-GlcNAcylation
PKCγ	GKGSFG K	1		Acetylation
	GKGSFG K	1	57	ubiquitination
PKCδ	GKGSFG K	3	21, 58,55
	GKGSFG K	1	57	ubiquitination
PKCε	GKGSFG K	1	23	O-GlcNAcylation
	GKGSFG K	1		Acetylation
PKCθ	GKGSFG K	1	56	ubiquitination
PKCη	GKGSFG K	2	55
RSK Subfamily
MSK1	GTGAYG	1
MSK2	KVL GTGAYG	3	56, 59, 60	ubiquitination
	KVL GTGAYG	1	61
	KVL GTGAYG	2	61
p70S6K	GKGGYG K	2	56, 62	ubiquitination
	GKGGYG K	2	56, 57	ubiquitination
RSK1	GQGSFG K	3	56, 59	ubiquitination	All RSK PTMs are located in the N-terminal kinase domain. PTMs have not been identified in RSK3.
	GQGSFG K	1		Acetylation
RSK2	GQGSFG K	3	48, 63, 64
	KVL GQGSFG	2	59	ubiquitination
RSK4	GQGSFG K	1		Acetylation
	GQGSFG K	3	56, 59	ubiquitination
CAMK Group
CaMK2
CaMK2α	GKGAFS	11	57	ubiquitination
	GKGAFS	3	65–67
CaMK2β	GKGAFS	8	57	ubiquitination
	GKGAFS	2	66, 67
CAMK2δ	GKGAFS	1	68	Acetylation
	GKGAFS	2	66, 67
CAMK2γ	GKGAFS	1	68	Acetylation
	GKGAFS	6		ubiquitination
	GKGAFS	2	66, 67
AMPKα1	TL GVGTFG	3	54, 64, 69
PIM1	GSGGFG	1
PIM2	GKGGFG	25	56, 60, 70	ubiquitination
CMGC Group
CDK1	GEGTYG	1846	13, 71–73
	GEGTYG	4125	13, 71–77
ERK2	SYI GEGAYG	1	47	Not in ERK1 where S is replaced by Q
	SYI GEGAYG	3		Sequence conserved in ERK1, but phosphorylation not detected
GSK3β	GNGSFG	2	48, 55	not in GSK3α
STE Group
MEK1	SEL GAGNGG	4	78
MEK2	SEL GAGNGG	1	79
Tyrosine Kinases
EGFRs
EGFR	GSGAFG TVY	8	48, 50, 51, 78, 80–82
	GSGAFG TVY	150	78, 80, 83–95
ErbB2	GSGAFG TVY	9	48, 50, 51, 78, 80, 81
	GSGAFG TVY	148	78, 80, 83–88, 90, 92, 93, 95, 96
ErbB3	GSGVFG	2	48, 53
ErbB4	GSGAFG TVY	7	48, 50, 51, 78, 80, 81
	GSGAFG TVY	147	78, 80, 83–88, 90, 92, 93, 95, 96
InsR	GQGSFG	5	43, 44, 46, 97, 98
IGF1R	GQGSFG MVY	1	48
	GQGSFG MVY	3	83
c-Abl	GGGQYG EVY	288	33, 39, 40, 86, 99
	GGGQYG EVY	339	32, 33, 39, 40, 54, 83, 86, 88, 92
Alk	GHGAFG EVY	22	100, 101

The data summarizes records curated by PhosphoSitePlus, a comprehensive online resource provided by Cell Signaling Technology. PhosphoSitePlus provides comprehensive information on post-translational modifications identified in studies that use both traditional low-throughput methods (i.e., studies that focus on few modification sites that are experimentally validated using robust techniques such as amino acid sequencing, phospho-specific antibodies, site-directed mutagenesis, dominant-negative constructs, etc.) as well as studies that use high throughput discovery mass spectrometry methods ¹⁰². Since the significance of a protein kinase G-loop PTM identified in only a single study using high-throughput MS methods is uncertain, these have generally not been included in the table, unless PTMs (phosphorylation, ubiquitination, acetylation, O-GlcNAcylation) are identified at multiple sites in or adjacent to the G-loop (or on the G-loops of multiple members of a single protein kinase subfamily).