We have conducted studies showing that the the LAR family of receptor protein tyrosine phosphatases are are binding partners for proteoglycan GAG chains. The binding of the different family members are not all the same. We have identified different regions in the extracellular domains of these molecules that bind GAG chains with different sulfation patterns. We have identified a novel binding site in Receptor Protein Tyrosine Phosphatase Sigma that binds Heparin Sulfate. In addition our data point to an additional receptor that binds bioactive CSPGs. A publication describing these results has been published. We have now demonstrated the the Lipid Phosphate Phosphatase-Related Proteins (LPPRs) can modulate neuronal adhesion and the cytoskeleton through interactions with RhoGDI that modulated both RhoA and Rac1 GTPases We have created knockout mice for the LPPR-1 and LPPR-3 and are now characterizing these mice. A paper describing these results is in preparation We have found that xylosides, compounds that are used to alter proteoglycan GAG chain composition, have significant actions at concentrations lower than those previously reported to reduce GAG chains can alter growth cone morphology. Evidence points to a novel signaling mechanism triggered by xylsides only at low concentrations.
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