Conformational rearrangements upon Syk auto-phosphorylation

Abstract

7 páginas, 3 figuras.Syk is a cytoplasmic tyrosine kinase that is activated after recruitment to immune receptors, triggering the phopshorylation of downstream targets. The kinase activity of Syk is controlled by an auto-inhibited conformation consisting of a regulatory region that contains two N-terminal Src homology 2 (SH2) domains inhibiting the catalytic activity of the kinase domain located at the C-terminus. The atomic structure of the related Zap-70 kinase and an electron microscopy (EM) model of Syk have revealed the structural mechanism of this auto-inhibition based on the formation of a compact conformation sustained by interactions between the regulatory and catalytic domains. On the other hand, the structural basis of Syk activation is not fully understood due to the lack of a 3D structure of full-length Syk in an active conformation. Here, we have used single-particle electron microscopy to analyse the conformational changes taking place in an activated form of Syk induced by auto-phosphorylation. The conformation of phosphorylated Syk is reminiscent of the compact structure of the inhibited protein but significant conformational changes are observed in the regulatory region. These rearrangements could be sufficient to disrupt the inhibitory interactions, contributing to Syk activation. These results suggest that the regulation of the activation of Syk might be modulated by subtle changes in the positioning of the regulatory domains rather than a full opening mechanism as proposed for the Src kinases.This work has been supported by projects and RD06/0020/1001 (OL) and RD06/0020/0001 (XB) of the “Red Temática de Investigación Cooperativa en Cáncer (RTICC)” from the “Instituto de Salud Carlos III”, and SAF2008-00451 (OL) and SAF2006-01789 (XB) from the Spanish Ministry of Science and Innovation. OL group is additionally supported by the Human Frontiers Science Program (RGP39/2008) and the Autonomous Region of Madrid (CAM S-BIO-0214-2006). XRB's work is also supported by grants from the NIH (5R01–CA73735–13) and the Castilla y León Autonomous Government (SA053A05 and GR97). The activities of the Centro de Investigación del Cáncer are partially supported by the Ramón Areces Foundation and by the Foundation for Cancer Research at the University of Salamanca. Ernesto Arias holds a contract of the Autonomous Region of Madrid (“Contrato de Personal Investigador de Apoyo, CPI”). M. Recuero-Checa is a FPI pre-doctoral fellow of the Spanish Ministry of SciencePeer reviewe