PMID: 24509848

 

    Legend: Sugar

Title : Glycosylation a t Asn211 regulates the activation state of the discoidin domain receptor 1 ( DDR1 )

Abstract :

1. Discoidin domain receptor 1 ( DDR1 ) belongs t o a unique family of receptor tyrosine kinases tha t signal in response t o collagens
2. DDR1 undergoes autophosphorylation in response t o collagen binding with a slow and sustained kinetics t ha t is unique among members of of the receptor tyrosine kinase family
3. DDR1 dimerization precedes receptor activation suggesting a structural inhibitory mechanism t o preven t unwa rr anted phosphorylation
4. However, the mechanism(s) tha t maintains the autoinhibitory state of the DDR1 dimers is unknown
5. Here, we repor t tha t N-glycosylation a t the Asn(211) residue plays a unique role in the control of DDR1 dimerization and autophosphorylation
6. Using site-directed mutagenesis, we found tha t mutations tha t disrup t the conserved (211)NDS N-glycosylation motif , bu t no t other N-glycosylation sites ( Asn(260), Asn(371), and Asn(394) ), resul t in collagen I-independen t constitutive phosphorylation
7. Mass spectrometry revealed tha t the N211Q mutan t undergoes phosphorylation a t Tyr(484), Tyr(520), Tyr(792), and Tyr(797)
8. The N211Q traffics t o the cell surface, and its ectodomain displays collagen I binding with an affinity similar t o tha t of the wild-type DDR1 ectodomain
9. However, unlike the wild-type receptor , the N211Q mutan t exhibits enhanced receptor dimerization and sustained activation upon ligand withdrawal
10. Taken together, these data sugges t tha t N-glycosylation a t the highly conserved (211)NDS motif evolved t o ac t as a negative repressor of DDR1 phosphorylation in the absence of ligand
11. The presence of glycan moieties a t tha t site may help t o lock the collagen-binding domain in the inactive state and preven t unwarranted signaling by receptor dimers
12. These studies provide a novel insigh t int o the structural mechanisms tha t regulate DDR activation