Protein phosphorylation, which plays a key role in most cellular activities, is a reversible process mediated by protein kinases and phosphoprotein phosphatases. Protein kinases catalyse the transfer of the gamma phosphate from nucleotide triphosphates (often ATP) to one or more amino acid residues in a protein substrate side chain, resulting in a conformational change affecting protein function. Phosphoprotein phosphatases catalyse the reverse process. Protein kinases fall into three broad classes, characterised with respect to substrate specificity []:Serine/threonine-protein kinasesTyrosine-protein kinasesDual specificity protein kinases (e.g. MEK - phosphorylates both Thr and Tyr on target proteins)Protein kinase function is evolutionarily conserved from Escherichia coli to human []. Protein kinases play a role in a multitude of cellular processes, including division, proliferation, apoptosis, and differentiation []. Phosphorylation usually results in a functional change of the target protein by changing enzyme activity, cellular location, or association with other proteins. The catalytic subunits of protein kinases are highly conserved, and several structures have been solved [], leading to large screens to develop kinase-specific inhibitors for the treatments of a number of diseases [].This represents serine/threonine-protein kinases (), such as Ulk1 and Ulk2 (Unc-51-Like Kinase). Ulk1 and Ulk2 regulate filopodia extension and branching of sensory axons. They are important for axon growth, playing an essential role in neurite extension of cerebellar granule cells [, ].
This entry represents a group of Serine/threonine-protein kinases, including Atg1 from yeasts, Unc-51 from C. elegans, Ulk1-3 from humans and ATG1a/b/c/t from Arabidopsis.Atg1 is required for vesicle formation in autophagy and the cytoplasm-to-vacuole targeting (Cvt) pathway [].Ulk1-3 are involved in autophagy in response to starvation [, ]. Ulk1 and Ulk2 regulate filopodia extension and branching of sensory axons. They are important for axon growth, playing an essential role in neurite extension of cerebellar granule cells [, ]. Unc-51 is important for axonal elongation and axonal guidance []. It is required for either the maintenance of axons (membrane turnover) or for an unknown neuronal function. C elegans worms lacking Unc-51 exhibit various abnormalities in axonal elongation and axonal structures. Unc-51 could also help control cell size along with Bec-1, as mutations in their corresponding genes results in a reduction in small body size without affecting cell number []. Unc-51 is also a component of the Unc-51/Atg-13 complex that is probably recruited by lgg-1 to preautophagosomes and is required for autophagosome formation [].In plants, the ATG1/13 complex is both a regulator and a target of autophagy [].
This the Atg13-binding region of Atg1 which comprises two tandem MIT (microtubule interacting and transport) domains, named tMIT [].Members of this entry are Serine/threonine-protein kinases, including Atg1 from yeasts, Unc-51 from C. elegans and Ulk1-2 from humans.Atg1 is required for vesicle formation in autophagy and the cytoplasm-to-vacuole targeting (Cvt) pathway [, ].Ulk1-2 are involved in autophagy in response to starvation [, ]. Ulk1 and Ulk2 regulate filopodia extension and branching of sensory axons. They are important for axon growth, playing an essential role in neurite extension of cerebellar granule cells [, ]. Unc-51 is important for axonal elongation and axonal guidance []. It is required for either the maintenance of axons (membrane turnover) or for an unknown neuronal function. C elegans worms lacking Unc-51 exhibit various abnormalities in axonal elongation and axonal structures. Unc-51 could also help control cell size along with Bec-1, as mutations in their corresponding genes results in a reduction in small body size without affecting cell number []. Unc-51 is also a component of the Unc-51/Atg-13 complex that is probably recruited by lgg-1 to preautophagosomes and is required for autophagosome formation [].
