Structural basis of syndecan-4 phosphorylation as a molecular switch to regulate signaling.
The syndecan transmembrane proteoglycans are involved in the organization of the actin cytoskeleton and have important roles as cell surface receptors during cell-matrix interactions. We have shown that the syndecan-4 cytoplasmic domain (4L) forms oligomeric complexes that bind to and stimulate PKCalpha activity in the presence of PtdIns(4,5)P2, emphasizing the importance of multimerization in the regulation of PKCalpha activation. Oligomerization of the cytoplasmic domain of syndecan-4 is regulated either positively by PtdIns(4,5)P2 or negatively by phosphorylation of serine 183. Phosphorylation results in reduced PKCalpha activity by inhibiting PtdIns(4,5)P2-dependent oligomerization of the syndecan-4 cytoplasmic domain. Data from NMR and gel-filtration chromatography show that the phosphorylated cytoplasmic domain (p-4L) exists as a dimer, similar to 4L, but not as higher-order oligomers. NMR analysis showed that the overall conformation of p-4L is a compact intertwined dimer with an unusually symmetric clamp shape, and its molecular surface is mostly positively charged. The two parallel strands form a cavity in the center of the dimeric twist. An especially marked effect of phosphorylation of the syndecan-4 cytoplasmic domain is a dramatic conformational change near the C2 region that ablates an interaction site with the PDZ domain of syntenin. Wound healing studies further suggest that syndecan-4 phosphorylation might influence cell migration behavior. We conclude that the phosphorylation (Ser183) of syndecan-4 can play a critical role as a molecular switch to regulate its functions through conformational change.
Koo
Bon-Kyung
BK
Department of Biochemistry and Protein Network Research Center, College of Science, Yonsei University, Seoul 120-749, South Korea.
Jung
Young Sang
YS
Shin
Joon
J
Han
Innoc
I
Mortier
Eva
E
Zimmermann
Pascale
P
Whiteford
James R
JR
Couchman
John R
JR
Oh
Eok-Soo
ES
Lee
Weontae
W
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002465:Cell Movement; D006224:Cricetinae; D004789:Enzyme Activation; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D011485:Protein Binding; D051571:Protein Kinase C-alpha / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011509:Proteoglycans / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction; D055672:Static Electricity; D013379:Substrate Specificity; D053671:Syndecan-4
D008562:Membrane Glycoproteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D011509:Proteoglycans; C508307:Sdc4 protein, rat; D053671:Syndecan-4; D010768:Phosphoserine; D051571:Protein Kinase C-alpha