Table 2.

IF protein PTMs, modifying enzymes, and methods of analysis

PTM	IFs	PTM enzyme (on)	PTM enzyme (off)	Tools for PTM analysis
Extensively studied
Phosphorylation	most IFs*	SAPKs, AKT1, PKC, Cdk1, Cdk5, other	PP1, PP2A	LC-MS; antibodies; phosphomutant transgenic mice; enzyme inhibitors
Farnesylation	lamins	farnesyl transferase	Zmpste24 (via proteolysis)	Zmpste−/− mice, FTIs
Ubiquitination	most IFs**	CHIP/STUB, Ubc3, UbcH5, Siah1, Trim32	not known	LC-MS, in vitro ubiquitination; stress models; proteasome inhibitors
Accumulating data
Sumoylation	lamins keratins vimentin	Ubc9	not known	LC-MS; in vitro sumoylation, SUMO antibodies
Glycosylation	keratins neurofilaments vimentin	OGT	O-GlcNAcase	LC-MS, transgenic mice (for example, K18-Gly-), antibodies (for example, NL6)
Acetylation	keratins	not known	SIRT2	LC-MS, pan-acetyllysine antibodies, acid-urea gels, deacetylase inhibitors
Limited data
Transamidation	keratins	transglutaminases	none	in vitro and in vivo cross-linking analysis
ADP ribosylation	desmin vimentin	ADP-ribosyl transferase SpyA	not known	LC-MS, in vitro ribosylation

^*phosphorylation of filensin, phakinin, and syncoilin is based on proteomic evidence

^**putative ubiquitination sites for most IFs have been identified by large scale proteomic studies