Structural studies of three cell signaling proteins : crystal structures of EphB1, PTPA, and YegS

Kinases and phosphatases are key regulatory proteins in the cell. The disruption of their activities leads ultimately to the abolishment of the homeostasis of the cell, and is frequently correlated with cancer. EphB1 is a member of the largest family of receptor tyrosine kinases. It is associated with neurogenesis, angiogenesis, and cancer. The cytosolic part of the human EphB1 receptor is composed of two domains. Successful generation of soluble constructs, using a novel random construct screening approach, led to the structure determination of the kinase domain of this receptor. The native structure and the complex structure with an ATP analogue revealed novel features in the regulation of the Eph family of kinases. The structure of PTPA, an activator of protein phosphatase 2 A, a tumor suppressor and a key phosphatase in the cell was solved. The structure revealed a novel fold containing a conserved cleft predicted to be involved in interaction with PP2A. Finally, the structure of YegS, an Escherichia coli protein annotated as a putative diacylglycerol kinase, has been determined. Beside the elucidation of its atomic structure, a phosphatidylglycerol (PG) kinase activity, never seen before, has been assigned to YegS based on biochemical studies. The YegS structure shows resemblance to the fold previously seen in NAD kinases. The structure also revealed the existence of a novel metal site that could potentially play a regulatory role. The YegS structure has important implications for understanding related proteins in pathogenic organisms and is the first homologue of a human lipid kinase for which the structure has been elucidated