The ULK1 Substrate Antibody Sampler Kit provides an economical means of detecting the activity of ULK1 using phospho-specific and control antibodies. The kit includes enough antibody to perform two western blot experiments with each primary antibody.
Specificity / Sensitivity
Phospho-Beclin-1 (Ser15) (D4B7R) Rabbit mAb and Phospho-Atg13 (Ser555) (E6H1W) Rabbit mAb are only recommended for transfected levels of their specific targets. Phospho-Atg13 (Ser555) (E6H1W) Rabbit mAb can weakly detect endogenous levels of phosphorylated Atg13, but also reacts with a band of unknown origin at 25 kDa. All other antibodies in the kit can detect endogenous levels of their specific targets. Phospho-ULK1 (Ser555) (D1H4) Rabbit mAb detects a band of unknown origin between 90 and 100 kDa.
Source / Purification
Monoclonal antibodies are produced by immunizing rabbits with synthetic peptides corresponding to residues surrounding Arg70 of human Atg14, Thr72 of human Beclin-1, Asp462 of human Atg13, and Arg600 of human ULK1. Phosphorylation-specific monoclonal antibodies are produced by immunizing rabbits with synthetic phospho-peptides corresponding to Ser29 of Atg14, Ser15 of human Beclin-1, Ser355 of human Atg13 (Ser318 of isoform 2 of Atg13), Ser555 of mouse ULK1 (equivalent to Ser556 of human ULK1), and Ser757 of mouse ULK1 (equivalent to Ser758 of human ULK1).
Two related serine/threonine kinases, UNC-51-like kinase 1 and 2 (ULK1, ULK2), were discovered as mammalian homologs of the C. elegans gene UNC-51 in which mutants exhibited abnormal axonal extension and growth (1-4). Both proteins are widely expressed and contain an amino-terminal kinase domain followed by a central proline/serine rich domain and a highly conserved carboxy-terminal domain. The roles of ULK1 and ULK2 in axon growth have been linked to studies showing that the kinases are localized to neuronal growth cones and are involved in endocytosis of critical growth factors, such as NGF (5). Yeast two-hybrid studies found ULK1/2 associated with modulators of the endocytic pathway, SynGAP and syntenin (6). Structural similarity of ULK1/2 has also been recognized with the yeast autophagy protein Atg1/Apg1 (7). Knockdown experiments using siRNA demonstrated that ULK1 is essential for autophagy (8), a catabolic process for the degradation of bulk cytoplasmic contents (9,10). It appears that Atg1/ULK1 can act as a convergence point for multiple signals that control autophagy (11), and can bind to several autophagy-related (Atg) proteins, regulating phosphorylation states and protein trafficking (12-16).
AMPK, activated during low nutrient conditions, directly phosphorylates ULK1 at multiple sites, including Ser317, Ser555, and Ser777 (17,18). Conversely, mTOR, which is a regulator of cell growth and is an inhibitor of autophagy, phosphorylates ULK1 at Ser757 and disrupts the interaction between ULK1 and AMPK (17). ULK1 has been shown to phoshorylate several targets in the autophagy pathway, including Ser29 of Atg14, Ser15 of Beclin-1, and Ser355 of Atg13 (19-22).