prolinedirected

Proline-directed refers to a class of protein phosphorylation events in which serine or threonine residues are phosphorylated when followed by a proline residue in the substrate sequence, producing SP or TP motifs. The term is used to describe both the substrate preference of certain kinases and the regulation of signaling pathways that depend on these specific phosphorylation sites. Kinases that are commonly described as proline-directed include the cyclin-dependent kinases (CDKs) and the mitogen-activated protein kinases (MAPKs), such as ERK, JNK, and p38. Other enzymes with proline-directed activity can target SP/TP motifs on select substrates, although their primary specificities may be broader or context-dependent.

Mechanistically, the presence of proline at the +1 position imposes conformational constraints that influence kinase recognition and the resulting conformational changes in substrates. This motif-based targeting enables coordinated regulation of processes such as cell cycle progression, transcriptional control, and responses to extracellular signals. For example, CDKs phosphorylate many cell cycle regulators at SP/TP sites to drive transitions between phases, while MAPKs modulate transcription factors and chromatin-associated proteins through proline-directed phosphorylation during growth, differentiation, and stress responses.

Detection and study typically rely on phosphoproteomics, with enrichment and mass spectrometry used to identify SP/TP phosphorylation sites, complemented by motif analysis and kinase-substrate mapping. Proline-directed phosphorylation is a foundational concept in signaling networks and is a focal point in cancer research and drug development, given the central roles of CDKs and MAPKs in proliferative signaling.