Many posttranslational modifications have been identified on functional groups of amino acid side chains in many proteins and
peptides over the years. In particularly, protein acetylation has been found to be a dynamic, reversible posttranslational modification that regulates many different biological pathways. Furthermore, more recently the propionylation of lysine side chains has been observed in proteins such as p53 and histones and is thought to play a role similar to acetylation in modulating protein activity. In the case of histones, the observed posttranslational modifications involved in epigenetic regulation mechanism has led to the so called “histone code.” Scientists know now that the acetylation status of various lysine residues on individual histones govern chromatin structure and regulates transcription. In addition, acetylation of metabolic enzymes, such as acetyl-CoA synthetase, has been found to regulate their activity. And many other posttranslational modifications have been also identified generating a whole list of postranslationally modified proteins involved in cell metabolism regulating pathways. This indicates that there appears to be a more general “protein code” which exact nature hopefully will be more clearly defined in the coming years. For example, it is well known that cytoskeleton proteins such as actin and tubulin as well as microtubule associated proteins are regulated, or their interactions are fined tuned, via posttranslational modifications such as phosphorylatin, acetylation and glutamylation, among others. Furthermore, more recently members of the sirtuin family of deacetylases have been shown to have depropionylation activities. In 2011 Bheda et al. determined the structure of a Thermotoga maritima sirtuin, Sir2Tm, bound to a propionylated peptide derived from p53 at a resolution of 1.8 A ˚. In addition the research group compared the structure of Sir2Tm bound to an acetylated peptide with the structure of Sir2Tm in complex with the propionylated p53 peptide at 1.8 A ˚ resolution. As expected, the overall structure was similar to the reported crystal structure of Sir2Tm bound to an acetylated p53 peptide and showed that hydrophobic residues in the active site shift to accommodate the bulkier propionyl group. Using isothermal titration calorimetry the researchers were able to show that Sir2Tm binds propionylated substrates more tightly than acetylated substrates, but kinetic assays revealed that the catalytic rate of Sir2Tm deacylation of propionyllysine is slightly reduced compared to acetyl-lysine. The researchers stated that their results allowed broadening of our understanding of the newly identified propionyl-lysine modification and the ability of sirtuins to depropionylate, as well as deacetylate, substrates. Propionyl-lysine modifications are chemically similar to acetylation but have one or two extra methylene groups. This makes this type of modification bulkier and more hydrophobic. Whereas acetyltransferases use acetyl-CoA as the acetyl group donor propionyltransferases and butyryltransferases catalyze the transfer of the acyl group from propionyl-CoA and butyryl-CoA to the ε-nitrogen of lysine. Other acetyltransferases such as the GCN5 family of acetyltransferases and P300 can utilize either acetyl-CoA or propionyl-CoA to acetylate or propionylate substrates, respectively. Acetylated and propionylated peptides can now be synthesized with high purity using standard Fmoc-based solid phase
peptide synthesis chemistries. Pools or arrays made of acetylated or propionylated peptides are useful for the study of their interactions with the target acetylgroup-transfer or binding proteins.
References
Poonam Bheda, Jennifer T. Wang, Jorge C. Escalante-Semerena, and Cynthia Wolberger; Structure of Sir2Tm bound to a propionylated peptide. PROTEIN SCIENCE 2011, VOL 20:131-139.
Chen Y, Sprung R, Tang Y, Ball H, Sangras B, Kim SC, Falck JR, Peng J, Gu W, Zhao Y (2007) Lysine propionylation and butyrylation are novel post-translational modifications in histones. Mol Cell Proteomics 6: 812-819.
Cheng Z, Tang Y, Chen Y, KimS, LiuH, Li SS,GuW, Zhao Y (2009) Molecular characterization of propionyllysines in non-histone proteins. Mol Cell Proteomics 8:45-52.
Garrity J, Gardner JG, Hawse W, Wolberger C, Escalante-Semerena JC (2007) N-lysine propionylation controls the activity of propionyl-CoA synthetase. J Biol Chem 282:30239-30245.
Starai VJ, Celic I, Cole RN, Boeke JD, Escalante-Semerena JC (2002) Sir2-dependent activation of acetyl-CoA synthetase by deacetylation of active lysine. Science 298:2390-2392.
Tanny JC, Moazed D (2001) Coupling of histone deacetylation to NAD breakdown by the yeast silencing protein Sir2: evidence for acetyl transfer from substrate to an NAD breakdown product. Proc Natl Acad Sci USA 98:415-420.