Table 1. Sites on myocyte enhancer factor-2D (MEF2D) phosphorylated by p38α or p38δ in vitro.

Human GST-MEF2D was incubated in a phosphorylation reaction mix containing Mg-ATP in the absence (control) or the presence of p38α or p38δ, and subjected to sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE). Phosphorylated MEF2D was excised from the gel, digested with trypsin and peptides separated as indicated in Materials and methods. Phosphorylated residues were identified by liquid chromatography–mass spectrometry (LC–MS)/MS. Peptides containing the phosphorylated residues are shown. Phosphorylated residues are indicated as pS in red, deaminated residues are indicated as (deam) in blue. (-) no or poor phosphorylation detected; (+) phosphorylation detected; (++) strong phosphorylation detected.

Protein phospho-site (Q14814)	Phosphopeptide	Control	p38α	p38δ
S98	KGFN(deam)GCDpSPEPDGEDSLEQSPLLEDK	+	+++	-
	KGFNGCDpSPEPDGEDSLEQSPLLEDK
	GFNGCDpSPEPDGEDSLEQSPLLEDK
	GFNGCDpSPEPDGEDSLEQSPLLEDKYR
S121	RApSEELDGLFR	+	+	+++
S180	LLpSPQQPALQR	-	+++	+++
S192	NSVpSPGLPQR	-	+	-
S231	ApSPGLLPVANGNSLNK	-	+	+++
	ApSPGLLPVAN(deam)GNSLNK
	ApSPGLLPVAN(deam)GN(deam)SLNK
S251	VIPAKpSPPPPTHSTQLGAPSR	-	+++	+++
	pSPPPPTHSTQLGAPSR
S275	VITpSQAGK	-	-	+++
S444	SEPVpSPSRER	-	-	+++
S450	ERpSPAPPPPAVFPAAR	-	+	+++
S472	PEPGDGLSpSPAGGSYETGDR	-	-	+++