Post-translational Modification
Post-translational modification (PTM) refers to the covalent chemical changes made to a protein after its synthesis by the ribosome, altering its activity, localisation, stability, or interactions with other molecules. Common modifications include phosphorylation, glycosylation, ubiquitination, acetylation, and methylation, each carried out by specific enzymes at defined amino acid residues. PTMs vastly expand the functional diversity of the proteome beyond what is encoded in the genome, and their dysregulation underpins diseases ranging from diabetes to neurodegeneration.
Common Post-translational Modifications
| Modification | Target Residue | Enzyme | Functional Effect |
|---|---|---|---|
| Phosphorylation | Ser, Thr, Tyr | Kinase / Phosphatase | Signal transduction, activation/inhibition |
| Glycosylation | Asn (N-linked), Ser/Thr (O-linked) | Glycosyltransferases | Protein folding, cell recognition |
| Ubiquitination | Lys | E1, E2, E3 ligases | Proteasomal degradation, DNA repair |
| Acetylation | Lys (histone tails) | Histone acetyltransferases | Chromatin remodelling, gene activation |
| Methylation | Lys, Arg | Methyltransferases | Transcriptional regulation, epigenetics |
| Sumoylation | Lys | SUMO ligases | Nuclear localisation, protein stability |
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Related Terms
Transcription Factor
A transcription factor is a protein that binds to specific DNA sequences in the promoter or enhancer regions of a gene to control the rate of transcription by RNA polymerase. These proteins act as molecular switches, either activating or repressing gene expression in response to developmental cues, environmental signals, or cellular needs. In humans, approximately 1,600 transcription factors have been identified, and their dysregulation is linked to cancers, developmental disorders, and metabolic diseases.
Central Dogma of Biology
The Central Dogma of Molecular Biology, formulated by Francis Crick in 1958, describes the general flow of genetic information within a biological system: DNA is transcribed into RNA, and RNA is translated into protein. Crick's original statement also specified that information transfer from protein back to nucleic acid does not normally occur, establishing a directional framework for gene expression. The discovery of reverse transcriptase in retroviruses revealed that RNA can also be reverse-transcribed into DNA, representing a known exception to the standard flow while still consistent with Crick's framework.
Restriction Enzyme
A restriction enzyme (restriction endonuclease) is a bacterial enzyme that cuts double-stranded DNA at or near a specific short nucleotide sequence called a recognition site, typically 4–8 base pairs in length. Bacteria produce these enzymes as part of a restriction-modification defence system to degrade foreign viral DNA that lacks the bacterium's own methylation marks. In molecular biology, type II restriction enzymes such as EcoRI and HindIII are indispensable tools for cutting DNA predictably to produce defined fragments with either blunt ends or "sticky" (cohesive) overhangs, enabling gene cloning, restriction mapping, and DNA fingerprinting.
From Latin "post" (after) + Latin "translatio" (a carrying across, from "transferre") + Latin "modificatio" (a measuring, from "modus" measure). The abbreviation PTM became standard in proteomics literature from the 1990s onwards.